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5 October 2016

Kees Cook: security things in Linux v4.8

Previously: v4.7. Here are a bunch of security things I m excited about in Linux v4.8: SLUB freelist ASLR Thomas Garnier continued his freelist randomization work by adding SLUB support. x86_64 KASLR text base offset physical/virtual decoupling On x86_64, to implement the KASLR text base offset, the physical memory location of the kernel was randomized, which resulted in the virtual address being offset as well. Due to how the kernel s -2GB addressing works (gcc s -mcmodel=kernel ), it wasn t possible to randomize the physical location beyond the 2GB limit, leaving any additional physical memory unused as a randomization target. In order to decouple the physical and virtual location of the kernel (to make physical address exposures less valuable to attackers), the physical location of the kernel needed to be randomized separately from the virtual location. This required a lot of work for handling very large addresses spanning terabytes of address space. Yinghai Lu, Baoquan He, and I landed a series of patches that ultimately did this (and in the process fixed some other bugs too). This expands the physical offset entropy to roughly $physical_memory_size_of_system / 2MB bits. x86_64 KASLR memory base offset Thomas Garnier rolled out KASLR to the kernel s various statically located memory ranges, randomizing their locations with CONFIG_RANDOMIZE_MEMORY. One of the more notable things randomized is the physical memory mapping, which is a known target for attacks. Also randomized is the vmalloc area, which makes attacks against targets vmalloced during boot (which tend to always end up in the same location on a given system) are now harder to locate. (The vmemmap region randomization accidentally missed the v4.8 window and will appear in v4.9.) x86_64 KASLR with hibernation Rafael Wysocki (with Thomas Garnier, Borislav Petkov, Yinghai Lu, Logan Gunthorpe, and myself) worked on a number of fixes to hibernation code that, even without KASLR, were coincidentally exposed by the earlier W^X fix. With that original problem fixed, then memory KASLR exposed more problems. I m very grateful everyone was able to help out fixing these, especially Rafael and Thomas. It s a hard place to debug. The bottom line, now, is that hibernation and KASLR are no longer mutually exclusive. gcc plugin infrastructure Emese Revfy ported the PaX/Grsecurity gcc plugin infrastructure to upstream. If you want to perform compiler-based magic on kernel builds, now it s much easier with CONFIG_GCC_PLUGINS! The plugins live in scripts/gcc-plugins/. Current plugins are a short example called Cyclic Complexity which just emits the complexity of functions as they re compiled, and Sanitizer Coverage which provides the same functionality as gcc s recent -fsanitize-coverage=trace-pc but back through gcc 4.5. Another notable detail about this work is that it was the first Linux kernel security work funded by Linux Foundation s Core Infrastructure Initiative. I m looking forward to more plugins! If you re on Debian or Ubuntu, the required gcc plugin headers are available via the gcc-$N-plugin-dev package (and similarly for all cross-compiler packages). hardened usercopy Along with work from Rik van Riel, Laura Abbott, Casey Schaufler, and many other folks doing testing on the KSPP mailing list, I ported part of PAX_USERCOPY (the basic runtime bounds checking) to upstream as CONFIG_HARDENED_USERCOPY. One of the interface boundaries between the kernel and user-space are the copy_to_user()/copy_from_user() family of functions. Frequently, the size of a copy is known at compile-time ( built-in constant ), so there s not much benefit in checking those sizes (hardened usercopy avoids these cases). In the case of dynamic sizes, hardened usercopy checks for 3 areas of memory: slab allocations, stack allocations, and kernel text. Direct kernel text copying is simply disallowed. Stack copying is allowed as long as it is entirely contained by the current stack memory range (and on x86, only if it does not include the saved stack frame and instruction pointers). For slab allocations (e.g. those allocated through kmem_cache_alloc() and the kmalloc()-family of functions), the copy size is compared against the size of the object being copied. For example, if copy_from_user() is writing to a structure that was allocated as size 64, but the copy gets tricked into trying to write 65 bytes, hardened usercopy will catch it and kill the process. For testing hardened usercopy, lkdtm gained several new tests: USERCOPY_HEAP_SIZE_TO, USERCOPY_HEAP_SIZE_FROM, USERCOPY_STACK_FRAME_TO,
USERCOPY_STACK_FRAME_FROM, USERCOPY_STACK_BEYOND, and USERCOPY_KERNEL. Additionally, USERCOPY_HEAP_FLAG_TO and USERCOPY_HEAP_FLAG_FROM were added to test what will be coming next for hardened usercopy: flagging slab memory as safe for copy to/from user-space , effectively whitelisting certainly slab caches, as done by PAX_USERCOPY. This further reduces the scope of what s allowed to be copied to/from, since most kernel memory is not intended to ever be exposed to user-space. Adding this logic will require some reorganization of usercopy code to add some new APIs, as PAX_USERCOPY s approach to handling special-cases is to add bounce-copies (copy from slab to stack, then copy to userspace) as needed, which is unlikely to be acceptable upstream. seccomp reordered after ptrace By its original design, seccomp filtering happened before ptrace so that seccomp-based ptracers (i.e. SECCOMP_RET_TRACE) could explicitly bypass seccomp filtering and force a desired syscall. Nothing actually used this feature, and as it turns out, it s not compatible with process launchers that install seccomp filters (e.g. systemd, lxc) since as long as the ptrace and fork syscalls are allowed (and fork is needed for any sensible container environment), a process could spawn a tracer to help bypass a filter by injecting syscalls. After Andy Lutomirski convinced me that ordering ptrace first does not change the attack surface of a running process (unless all syscalls are blacklisted, the entire ptrace attack surface will always be exposed), I rearranged things. Now there is no (expected) way to bypass seccomp filters, and containers with seccomp filters can allow ptrace again. That s it for v4.8! The merge window is open for v4.9

2016, Kees Cook. This work is licensed under a Creative Commons Attribution-ShareAlike 3.0 License.
Creative Commons License

4 October 2016

Iain R. Learmonth: Decentralise (in a kind of centralised way)

Once a month I am involved in running an informal session, loosely affiliated with Open Rights Group and FSFE, called Cryptonoise. Cryptonoise explores methods for protecting your digital rights, with a leaning towards focusing on privacy, and provides a venue for like minded people to meet up and discuss the state of the digital landscape and those that may try to infringe on the rights of digital citizens. We ve all made it easy for large enterprises and governments to collect masses of data about our online activities because we perform most of those activities in the same place. Facebook, Google and Twitter spring to mind as examples of companies that have grown to dangerous sizes with little competition. This is not paranoia. This is real. We make it a lot more difficult when we spread out. Our meetups are held at 57North Hacklab and at the last meetup on the 29th September I set up a GNU Social instance for the members of 57North. GNU Social provides the same functionality as Twitter but as a decentralised federated network. Federation is a feature that is found in protocols like E-Mail, XMPP and SIP. It doesn t matter which server you re using, you can still talk to all the other users on all the other servers. While I m using social.57north.org.uk I can still follow FSF on status.fsf.org, for example, with no prior coordination with system administrators or anything complicated. It all just works. People have pointed out that I ve just introduced another point of centralisation but I don t see it necessarily as a bad thing. I think too many users in a single service starts to look dangerous but as long as user counts don t go too high I believe that the benefits of sharing the administrative workload (performing updates, monitoring, keeping the TLS cert current, etc.) far outweigh the effects of having a few extra users. I think 100 is probably about the maximum number I would be comfortable with, although I ll admit I ve not based this on anything and it s chosen arbitrarily. The jabber.ccc.de server is an example of a service that grew too large. It was set up by members of CCC and made available to all, but ended up becoming the de facto service for hackers. The jabber.ccc.de team have made appeals for others to set up their own servers, and you should. For a great overview and guide for setting up your own real-time commmunication servers, check out the RTC Quick Start Guide. This work was enabled by Shell who had previously set up a Central Authentication Service, which GNU Social already had a plugin to use as the authentication backend. No one likes to have a whole load of different passwords for different services and integration with this allows for identities to be consistent across the 57North services. She has also setup a Matrix homeserver, another step towards decentralisation and an end of reliance on centralised giants. If you have an account on a GNU Social instance, you can follow me here.

3 October 2016

Matthew Garrett: The importance of paying attention in building community trust

Trust is important in any kind of interpersonal relationship. It's inevitable that there will be cases where something you do will irritate or upset others, even if only to a small degree. Handling small cases well helps build trust that you will do the right thing in more significant cases, whereas ignoring things that seem fairly insignificant (or saying that you'll do something about them and then failing to do so) suggests that you'll also fail when there's a major problem. Getting the small details right is a major part of creating the impression that you'll deal with significant challenges in a responsible and considerate way.

This isn't limited to individual relationships. Something that distinguishes good customer service from bad customer service is getting the details right. There are many industries where significant failures happen infrequently, but minor ones happen a lot. Would you prefer to give your business to a company that handles those small details well (even if they're not overly annoying) or one that just tells you to deal with them?

And the same is true of software communities. A strong and considerate response to minor bug reports makes it more likely that users will be patient with you when dealing with significant ones. Handling small patch contributions quickly makes it more likely that a submitter will be willing to do the work of making more significant contributions. These things are well understood, and most successful projects have actively worked to reduce barriers to entry and to be responsive to user requests in order to encourage participation and foster a feeling that they care.

But what's often ignored is that this applies to other aspects of communities as well. Failing to use inclusive language may not seem like a big thing in itself, but it leaves people with the feeling that you're less likely to do anything about more egregious exclusionary behaviour. Allowing a baseline level of sexist humour gives the impression that you won't act if there are blatant displays of misogyny. The more examples of these "insignificant" issues people see, the more likely they are to choose to spend their time somewhere else, somewhere they can have faith that major issues will be handled appropriately.

There's a more insidious aspect to this. Sometimes we can believe that we are handling minor issues appropriately, that we're acting in a way that handles people's concerns, while actually failing to do so. If someone raises a concern about an aspect of the community, it's important to discuss solutions with them. Putting effort into "solving" a problem without ensuring that the solution has the desired outcome is not only a waste of time, it alienates those affected even more - they're now not only left with the feeling that they can't trust you to respond appropriately, but that you will actively ignore their feelings in the process.

It's not always possible to satisfy everybody's concerns. Sometimes you'll be left in situations where you have conflicting requests. In that case the best thing you can do is to explain the conflict and why you've made the choice you have, and demonstrate that you took this issue seriously rather than ignoring it. Depending on the issue, you may still alienate some number of participants, but it'll be fewer than if you just pretend that it's not actually a problem.

One warning, though: while building trust in this way enhances people's willingness to join your community, it also builds expectations. If a significant issue does arise, and if you fail to handle it well, you'll burn a lot of that trust in the process. The fact that you've built that trust in the first place may be what saves your community from disintegrating completely, but people will feel even more betrayed if you don't actively work to rebuild it. And if there's a pattern of mishandling major problems, no amount of getting the details right will matter.

Communities that ignore these issues are, long term, likely to end up weaker than communities that pay attention to them. Making sure you get this right in the first place, and setting expectations that you will pay attention to your contributors, is a vital part of building a meaningful relationship between your community and its members.

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Kees Cook: security things in Linux v4.7

Previously: v4.6. Onward to security things I found interesting in Linux v4.7: KASLR text base offset for MIPS Matt Redfearn added text base address KASLR to MIPS, similar to what s available on x86 and arm64. As done with x86, MIPS attempts to gather entropy from various build-time, run-time, and CPU locations in an effort to find reasonable sources during early-boot. MIPS doesn t yet have anything as strong as x86 s RDRAND (though most have an instruction counter like x86 s RDTSC), but it does have the benefit of being able to use Device Tree (i.e. the /chosen/kaslr-seed property) like arm64 does. By my understanding, even without Device Tree, MIPS KASLR entropy should be as strong as pre-RDRAND x86 entropy, which is more than sufficient for what is, similar to x86, not a huge KASLR range anyway: default 8 bits (a span of 16MB with 64KB alignment), though CONFIG_RANDOMIZE_BASE_MAX_OFFSET can be tuned to the device s memory, giving a maximum of 11 bits on 32-bit, and 15 bits on EVA or 64-bit. SLAB freelist ASLR Thomas Garnier added CONFIG_SLAB_FREELIST_RANDOM to make slab allocation layouts less deterministic with a per-boot randomized freelist order. This raises the bar for successful kernel slab attacks. Attackers will need to either find additional bugs to help leak slab layout information or will need to perform more complex grooming during an attack. Thomas wrote a post describing the feature in more detail here: Randomizing the Linux kernel heap freelists. (SLAB is done in v4.7, and SLUB in v4.8.) eBPF JIT constant blinding Daniel Borkmann implemented constant blinding in the eBPF JIT subsystem. With strong kernel memory protections (CONFIG_DEBUG_RODATA) in place, and with the segregation of user-space memory execution from kernel (i.e SMEP, PXN, CONFIG_CPU_SW_DOMAIN_PAN), having a place where user-space can inject content into an executable area of kernel memory becomes very high-value to an attacker. The eBPF JIT was exactly such a thing: the use of BPF constants could result in the JIT producing instruction flows that could include attacker-controlled instructions (e.g. by directing execution into the middle of an instruction with a constant that would be interpreted as a native instruction). The eBPF JIT already uses a number of other defensive tricks (e.g. random starting position), but this added randomized blinding to any BPF constants, which makes building a malicious execution path in the eBPF JIT memory much more difficult (and helps block attempts at JIT spraying to bypass other protections). Elena Reshetova updated a 2012 proof-of-concept attack to succeed against modern kernels to help provide a working example of what needed fixing in the JIT. This serves as a thorough regression test for the protection. The cBPF JITs that exist in ARM, MIPS, PowerPC, and Sparc still need to be updated to eBPF, but when they do, they ll gain all these protections immediatley. Bottom line is that if you enable the (disabled-by-default) bpf_jit_enable sysctl, be sure to set the bpf_jit_harden sysctl to 2 (to perform blinding even for root). fix brk ASLR weakness on arm64 compat There have been a few ASLR fixes recently (e.g. ET_DYN, x86 32-bit unlimited stack), and while reviewing some suggested fixes to arm64 brk ASLR code from Jon Medhurst, I noticed that arm64 s brk ASLR entropy was slightly too low (less than 1 bit) for 64-bit and noticeably lower (by 2 bits) for 32-bit compat processes when compared to native 32-bit arm. I simplified the code by using literals for the entropy. Maybe we can add a sysctl some day to control brk ASLR entropy like was done for mmap ASLR entropy. LoadPin LSM LSM stacking is well-defined since v4.2, so I finally upstreamed a small LSM that implements a protection I wrote for Chrome OS several years back. On systems with a static root of trust that extends to the filesystem level (e.g. Chrome OS s coreboot+depthcharge boot firmware chaining to dm-verity, or a system booting from read-only media), it s redundant to sign kernel modules (you ve already got the modules on read-only media: they can t change). The kernel just needs to know they re all coming from the correct location. (And this solves loading known-good firmware too, since there is no convention for signed firmware in the kernel yet.) LoadPin requires that all modules, firmware, etc come from the same mount (and assumes that the first loaded file defines which mount is correct , hence load pinning ). That s it for v4.7. Prepare yourself for v4.8 next!

2016, Kees Cook. This work is licensed under a Creative Commons Attribution-ShareAlike 3.0 License.
Creative Commons License

2 October 2016

Steinar H. Gunderson: SNMP MIB setup

If you just install the snmp package out of the box, you won't get the MIBs, so it's pretty much useless for anything vendor without some setup. I'm sure this is documented somewhere, but I have to figure it out afresh every single time, so this time I'm writing it down; I can't possibly be the only one getting confused. First, install snmp-mibs-downloader from non-free. You'll need to work around bug #839574 to get the Cisco MIBs right: 
# cp /usr/share/doc/snmp-mibs-downloader/examples/cisco.conf /etc/snmp-mibs-downloader/
# gzip -cd /usr/share/doc/snmp-mibs-downloader/examples/ciscolist.gz > /etc/snmp-mibs-downloader/ciscolist
Now you can download the Cisco MIBs: 
# download-mibs cisco
However, this only downloads them; you will need to modify snmp.conf to actually use them. Comment out the line that says mibs : , and then add: 
mibdirs +/var/lib/snmp/mibs/cisco/
Voila! Now you can use snmpwalk with e.g. -m AIRESPACE-WIRELESS-MIB to get the full range of Cisco WLC objects (and the first time you do so as root or the Debian-snmp user, the MIBs will be indexed in /var/lib/snmp/mib_indexes/.)

1 October 2016

David Moreno: Thanks Debian

I sent this email to debian-private a few days ago, on the 10th anniversary of my Debian account creation: 
Date: Fri, 14 Aug 2015 19:37:20 +0200
From: David Moreno 
To: debian-private@lists.debian.org
Subject: Retiring from Debian
User-Agent: Mutt/1.5.23 (2014-03-12)
[-- PGP output follows (current time: Sun 23 Aug 2015 06:18:36 PM CEST) --]
gpg: Signature made Fri 14 Aug 2015 07:37:20 PM CEST using RSA key ID 4DADEC2F
gpg: Good signature from "David Moreno "
gpg:                 aka "David Moreno "
gpg:                 aka "David Moreno (1984-08-08) "
[-- End of PGP output --]
[-- The following data is signed --]
Hi,
Ten years ago today (2005-08-14) my account was created:
https://nm.debian.org/public/person/damog
Today, I don't feel like Debian represents me and neither do I represent the
project anymore.
I had tried over the last couple of years to retake my involvement but lack of
motivation and time always got on the way, so the right thing to do for me is
to officially retire and gtfo.
I certainly learned a bunch from dozens of Debian people over these many years,
and I'm nothing but grateful with all of them; I will for sure carry the project
close to my heart   as I carry it with the Debian swirl I still have tattooed
on my back ;)
http://damog.net/blog/2005/06/29/debian-tattoo/
I have three packages left that have not been updated in forever and you can
consider orphaned now: gcolor2, libperl6-say-perl and libxml-treepp-perl.
With all best wishes,
David Moreno.
http://damog.net/
[-- End of signed data --]
I received a couple of questions about my decision here. I basically don t feel like Debian represents my interests and neither do I represent the project this doesn t mean I don t believe in free software, to the contrary. I think some of the best software advancements we ve made as society are thanks to it. I don t necessarily believe on how the project has evolved itself, whether that has been the right way, to regain relevancy and dominance, and if it s remained primarily a way to feed dogmatism versus pragmatism. This is the perfect example of a tragic consequence. I was very happy to learn that the current Debian Conference being held in Germany got the highest attendance ever, hopefully that can be utilized in a significant and useful way. Regardless, my contributions to Debian were never noteworthy so it s also not that big of a deal. I just need to close cycles myself and move forward, and the ten year anniversary looked like a significant mark for that. Poke me in case you wanna discuss some more. I ll always be happy to. Specially over beer :) Peace.

Kees Cook: security things in Linux v4.6

Previously: v4.5. The v4.6 Linux kernel release included a bunch of stuff, with much more of it under the KSPP umbrella. seccomp support for parisc Helge Deller added seccomp support for parisc, which including plumbing support for PTRACE_GETREGSET to get the self-tests working. x86 32-bit mmap ASLR vs unlimited stack fixed Hector Marco-Gisbert removed a long-standing limitation to mmap ASLR on 32-bit x86, where setting an unlimited stack (e.g. ulimit -s unlimited ) would turn off mmap ASLR (which provided a way to bypass ASLR when executing setuid processes). Given that ASLR entropy can now be controlled directly (see the v4.5 post), and that the cases where this created an actual problem are very rare, means that if a system sees collisions between unlimited stack and mmap ASLR, they can just adjust the 32-bit ASLR entropy instead. x86 execute-only memory Dave Hansen added Protection Key support for future x86 CPUs and, as part of this, implemented support for execute only memory in user-space. On pkeys-supporting CPUs, using mmap(..., PROT_EXEC) (i.e. without PROT_READ) will mean that the memory can be executed but cannot be read (or written). This provides some mitigation against automated ROP gadget finding where an executable is read out of memory to find places that can be used to build a malicious execution path. Using this will require changing some linker behavior (to avoid putting data in executable areas), but seems to otherwise Just Work. I m looking forward to either emulated QEmu support or access to one of these fancy CPUs. CONFIG_DEBUG_RODATA enabled by default on arm and arm64, and mandatory on x86 Ard Biesheuvel (arm64) and I (arm) made the poorly-named CONFIG_DEBUG_RODATA enabled by default. This feature controls whether the kernel enforces proper memory protections on its own memory regions (code memory is executable and read-only, read-only data is actually read-only and non-executable, and writable data is non-executable). This protection is a fundamental security primitive for kernel self-protection, so making it on-by-default is required to start any kind of attack surface reduction within the kernel. On x86 CONFIG_DEBUG_RODATA was already enabled by default, but, at Ingo Molnar s suggestion, I made it mandatory: CONFIG_DEBUG_RODATA cannot be turned off on x86. I expect we ll get there with arm and arm64 too, but the protection is still somewhat new on these architectures, so it s reasonable to continue to leave an out for developers that find themselves tripping over it. arm64 KASLR text base offset Ard Biesheuvel reworked a ton of arm64 infrastructure to support kernel relocation and, building on that, Kernel Address Space Layout Randomization of the kernel text base offset (and module base offset). As with x86 text base KASLR, this is a probabilistic defense that raises the bar for kernel attacks where finding the KASLR offset must be added to the chain of exploits used for a successful attack. One big difference from x86 is that the entropy for the KASLR must come either from Device Tree (in the /chosen/kaslr-seed property) or from UEFI (via EFI_RNG_PROTOCOL), so if you re building arm64 devices, make sure you have a strong source of early-boot entropy that you can expose through your boot-firmware or boot-loader. zero-poison after free Laura Abbott reworked a bunch of the kernel memory management debugging code to add zeroing of freed memory, similar to PaX/Grsecurity s PAX_MEMORY_SANITIZE feature. This feature means that memory is cleared at free, wiping any sensitive data so it doesn t have an opportunity to leak in various ways (e.g. accidentally uninitialized structures or padding), and that certain types of use-after-free flaws cannot be exploited since the memory has been wiped. To take things even a step further, the poisoning can be verified at allocation time to make sure that nothing wrote to it between free and allocation (called sanity checking ), which can catch another small subset of flaws. To understand the pieces of this, it s worth describing that the kernel s higher level allocator, the page allocator (e.g. __get_free_pages()) is used by the finer-grained slab allocator (e.g. kmem_cache_alloc(), kmalloc()). Poisoning is handled separately in both allocators. The zero-poisoning happens at the page allocator level. Since the slab allocators tend to do their own allocation/freeing, their poisoning happens separately (since on slab free nothing has been freed up to the page allocator). Only limited performance tuning has been done, so the penalty is rather high at the moment, at about 9% when doing a kernel build workload. Future work will include some exclusion of frequently-freed caches (similar to PAX_MEMORY_SANITIZE), and making the options entirely CONFIG controlled (right now both CONFIGs are needed to build in the code, and a kernel command line is needed to activate it). Performing the sanity checking (mentioned above) adds another roughly 3% penalty. In the general case (and once the performance of the poisoning is improved), the security value of the sanity checking isn t worth the performance trade-off. Tests for the features can be found in lkdtm as READ_AFTER_FREE and READ_BUDDY_AFTER_FREE. If you re feeling especially paranoid and have enabled sanity-checking, WRITE_AFTER_FREE and WRITE_BUDDY_AFTER_FREE can test these as well. To perform zero-poisoning of page allocations and (currently non-zero) poisoning of slab allocations, build with:
CONFIG_DEBUG_PAGEALLOC=n
CONFIG_PAGE_POISONING=y
CONFIG_PAGE_POISONING_NO_SANITY=y
CONFIG_PAGE_POISONING_ZERO=y
CONFIG_SLUB_DEBUG=y
and enable the page allocator poisoning and slab allocator poisoning at boot with this on the kernel command line:
page_poison=on slub_debug=P
To add sanity-checking, change PAGE_POISONING_NO_SANITY=n, and add F to slub_debug as slub_debug=PF . read-only after init I added the infrastructure to support making certain kernel memory read-only after kernel initialization (inspired by a small part of PaX/Grsecurity s KERNEXEC functionality). The goal is to continue to reduce the attack surface within the kernel by making even more of the memory, especially function pointer tables, read-only (which depends on CONFIG_DEBUG_RODATA above). Function pointer tables (and similar structures) are frequently targeted by attackers when redirecting execution. While many are already declared const in the kernel source code, making them read-only (and therefore unavailable to attackers) for their entire lifetime, there is a class of variables that get initialized during kernel (and module) start-up (i.e. written to during functions that are marked __init ) and then never (intentionally) written to again. Some examples are things like the VDSO, vector tables, arch-specific callbacks, etc. As it turns out, most architectures with kernel memory protection already delay making their data read-only until after __init (see mark_rodata_ro()), so it s trivial to declare a new data section ( .data..ro_after_init ) and add it to the existing read-only data section ( .rodata ). Kernel structures can be annotated with the new section (via the __ro_after_init macro), and they ll become read-only once boot has finished. The next step for attack surface reduction infrastructure will be to create a kernel memory region that is passively read-only, but can be made temporarily writable (by a single un-preemptable CPU), for storing sensitive structures that are written to only very rarely. Once this is done, much more of the kernel s attack surface can be made read-only for the majority of its lifetime. As people identify places where __ro_after_init can be used, we can grow the protection. A good place to start is to look through the PaX/Grsecurity patch to find uses of __read_only on variables that are only written to during __init functions. The rest are places that will need the temporarily-writable infrastructure (PaX/Grsecurity uses pax_open_kernel()/pax_close_kernel() for these). That s it for v4.6, next up will be v4.7!

2016, Kees Cook. This work is licensed under a Creative Commons Attribution-ShareAlike 3.0 License.
Creative Commons License

29 September 2016

Dirk Eddelbuettel: RcppCNPy 0.2.6

A new version of the RcppCNPy package arrived on CRAN a few days ago. RcppCNPy provides R with read and write access to NumPy files thanks to the cnpy library by Carl Rogers. This new release reflects all the suggestions and comments I received during the review process for the Journal of Open Source Software submission. I am happy to say that about twenty-nine days after I submitted, the paper was accepted and is now published.
Changes in version 0.2.6 (2016-09-25)
  • Expanded documentation in README.md
  • Added examples to help page
  • Added CITATION file for JOSS paper
CRANberries also provides a diffstat report for the latest release. As always, feedback is welcome and the best place to start a discussion may be the GitHub issue tickets page.

This post by Dirk Eddelbuettel originated on his Thinking inside the box blog. Please report excessive re-aggregation in third-party for-profit settings.

28 September 2016

Kees Cook: security things in Linux v4.5

Previously: v4.4. Some things I found interesting in the Linux kernel v4.5: CONFIG_IO_STRICT_DEVMEM The CONFIG_STRICT_DEVMEM setting that has existed for a long time already protects system RAM from being accessible through the /dev/mem device node to root in user-space. Dan Williams added CONFIG_IO_STRICT_DEVMEM to extend this so that if a kernel driver has reserved a device memory region for use, it will become unavailable to /dev/mem also. The reservation in the kernel was to keep other kernel things from using the memory, so this is just common sense to make sure user-space can t stomp on it either. Everyone should have this enabled. (And if you have a system where you discover you need IO memory access from userspace, you can boot with iomem=relaxed to disable this at runtime.) If you re looking to create a very bright line between user-space having access to device memory, it s worth noting that if a device driver is a module, a malicious root user can just unload the module (freeing the kernel memory reservation), fiddle with the device memory, and then reload the driver module. So either just leave out /dev/mem entirely (not currently possible with upstream), build a monolithic kernel (no modules), or otherwise block (un)loading of modules (/proc/sys/kernel/modules_disabled). ptrace fsuid checking Jann Horn fixed some corner-cases in how ptrace access checks were handled on special files in /proc. For example, prior to this fix, if a setuid process temporarily dropped privileges to perform actions as a regular user, the ptrace checks would not notice the reduced privilege, possibly allowing a regular user to trick a privileged process into disclosing things out of /proc (ASLR offsets, restricted directories, etc) that they normally would be restricted from seeing. ASLR entropy sysctl Daniel Cashman standardized the way architectures declare their maximum user-space ASLR entropy (CONFIG_ARCH_MMAP_RND_BITS_MAX) and then created a sysctl (/proc/sys/vm/mmap_rnd_bits) so that system owners could crank up entropy. For example, the default entropy on 32-bit ARM was 8 bits, but the maximum could be as much as 16. If your 64-bit kernel is built with CONFIG_COMPAT, there s a compat version of the sysctl as well, for controlling the ASLR entropy of 32-bit processes: /proc/sys/vm/mmap_rnd_compat_bits. Here s how to crank your entropy to the max, without regard to what architecture you re on: 
for i in "" "compat_"; do f=/proc/sys/vm/mmap_rnd_$ i bits; n=$(cat $f); while echo $n > $f ; do n=$(( n + 1 )); done; done
strict sysctl writes Two years ago I added a sysctl for treating sysctl writes more like regular files (i.e. what s written first is what appears at the start), rather than like a ring-buffer (what s written last is what appears first). At the time it wasn t clear what might break if this was enabled, so a WARN was added to the kernel. Since only one such string showed up in searches over the last two years, the strict writing mode was made the default. The setting remains available as /proc/sys/kernel/sysctl_writes_strict. seccomp UM support Micka l Sala n added seccomp support (and selftests) for user-mode Linux. Moar architectures! seccomp NNP vs TSYNC fix Jann Horn noticed and fixed a problem where if a seccomp filter was already in place on a process (after being installed by a privileged process like systemd, a container launcher, etc) then the setting of the no new privs flag could be bypassed when adding filters with the SECCOMP_FILTER_FLAG_TSYNC flag set. Bypassing NNP meant it might be possible to trick a buggy setuid program into doing things as root after a seccomp filter forced a privilege drop to fail (generally referred to as the sendmail setuid flaw ). With NNP set, a setuid program can t be run in the first place. That s it! Next I ll cover v4.6 Edit: Added notes about iomem=

2016, Kees Cook. This work is licensed under a Creative Commons Attribution-ShareAlike 3.0 License.
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Sean Whitton: 'Do you really need to do that?'

A new postdoc student arrived at our department this semester, and after learning that he uses GNU/Linux for all his computing, I invited him along to TFUG. During some of our meetings people asked how could I do X on my GNU/Linux desktop? and, jokingly, the postdoc would respond the answer to your question is do you really need to do that? Sometimes the more experienced GNU/Linux users at the table would respond to questions by suggesting that the user should simply give up on doing X, and the postdoc would slap his thigh and laugh and say see? I told you that s the answer! The phenomenon here is that people who have at some point made a commitment to at least try to use GNU/Linux for all their computing quickly find that they have come to value using GNU/Linux more than they value engaging in certain activities that only work well/at all under a proprietary operating system. I think that this is because they get used to being treated with respect by their computer. And indeed, one of the reasons I ve almost entirely given up on computer gaming is that computer games are non-free software. Are you sure you need to do that? starts sounding like a genuine question rather than simply a polite way of saying that what someone wants to do can t be achieved. I suggest that this is a blessing in disguise. The majority of the things that you can only do under a proprietary operating system are things that it would be good for you if you were to switch them out for other activities. I m not suggesting that switching to a GNU/Linux is a good way to give up on the entertainment industry. It s a good way of moderating your engagement with the entertainment industry. Rather than logging onto Netflix, you might instead pop in a DVD of a movie. You can still engage with contemporary popular culture, but the technical barriers give you an opportunity to moderate your consumption: once you ve finished watching the movie, the software won t try to get you to watch something else by making a calculation as to what you re most likely to assent to watching next based on what you ve watched before. For this behaviour of the Netflix software is just another example of non-free software working against its user s interests: watching a movie is good for you, but binge-watching a TV series probably isn t. In cases like this, living in the world of Free Software makes it easier to engage with media healthily.

26 September 2016

Kees Cook: security things in Linux v4.3

When I gave my State of the Kernel Self-Protection Project presentation at the 2016 Linux Security Summit, I included some slides covering some quick bullet points on things I found of interest in recent Linux kernel releases. Since there wasn t a lot of time to talk about them all, I figured I d make some short blog posts here about the stuff I was paying attention to, along with links to more information. This certainly isn t everything security-related or generally of interest, but they re the things I thought needed to be pointed out. If there s something security-related you think I should cover from v4.3, please mention it in the comments. I m sure I haven t caught everything. :) A note on timing and context: the momentum for starting the Kernel Self Protection Project got rolling well before it was officially announced on November 5th last year. To that end, I included stuff from v4.3 (which was developed in the months leading up to November) under the umbrella of the project, since the goals of KSPP aren t unique to the project nor must the goals be met by people that are explicitly participating in it. Additionally, not everything I think worth mentioning here technically falls under the kernel self-protection ideal anyway some things are just really interesting userspace-facing features. So, to that end, here are things I found interesting in v4.3: CONFIG_CPU_SW_DOMAIN_PAN Russell King implemented this feature for ARM which provides emulated segregation of user-space memory when running in kernel mode, by using the ARM Domain access control feature. This is similar to a combination of Privileged eXecute Never (PXN, in later ARMv7 CPUs) and Privileged Access Never (PAN, coming in future ARMv8.1 CPUs): the kernel cannot execute user-space memory, and cannot read/write user-space memory unless it was explicitly prepared to do so. This stops a huge set of common kernel exploitation methods, where either a malicious executable payload has been built in user-space memory and the kernel was redirected to run it, or where malicious data structures have been built in user-space memory and the kernel was tricked into dereferencing the memory, ultimately leading to a redirection of execution flow. This raises the bar for attackers since they can no longer trivially build code or structures in user-space where they control the memory layout, locations, etc. Instead, an attacker must find areas in kernel memory that are writable (and in the case of code, executable), where they can discover the location as well. For an attacker, there are vastly fewer places where this is possible in kernel memory as opposed to user-space memory. And as we continue to reduce the attack surface of the kernel, these opportunities will continue to shrink. While hardware support for this kind of segregation exists in s390 (natively separate memory spaces), ARM (PXN and PAN as mentioned above), and very recent x86 (SMEP since Ivy-Bridge, SMAP since Skylake), ARM is the first upstream architecture to provide this emulation for existing hardware. Everyone running ARMv7 CPUs with this kernel feature enabled suddenly gains the protection. Similar emulation protections (PAX_MEMORY_UDEREF) have been available in PaX/Grsecurity for a while, and I m delighted to see a form of this land in upstream finally. To test this kernel protection, the ACCESS_USERSPACE and EXEC_USERSPACE triggers for lkdtm have existed since Linux v3.13, when they were introduced in anticipation of the x86 SMEP and SMAP features. Ambient Capabilities Andy Lutomirski (with Christoph Lameter and Serge Hallyn) implemented a way for processes to pass capabilities across exec() in a sensible manner. Until Ambient Capabilities, any capabilities available to a process would only be passed to a child process if the new executable was correctly marked with filesystem capability bits. This turns out to be a real headache for anyone trying to build an even marginally complex least privilege execution environment. The case that Chrome OS ran into was having a network service daemon responsible for calling out to helper tools that would perform various networking operations. Keeping the daemon not running as root and retaining the needed capabilities in children required conflicting or crazy filesystem capabilities organized across all the binaries in the expected tree of privileged processes. (For example you may need to set filesystem capabilities on bash!) By being able to explicitly pass capabilities at runtime (instead of based on filesystem markings), this becomes much easier. For more details, the commit message is well-written, almost twice as long as than the code changes, and contains a test case. If that isn t enough, there is a self-test available in tools/testing/selftests/capabilities/ too. PowerPC and Tile support for seccomp filter Michael Ellerman added support for seccomp to PowerPC, and Chris Metcalf added support to Tile. As the seccomp maintainer, I get excited when an architecture adds support, so here we are with two. Also included were updates to the seccomp self-tests (in tools/testing/selftests/seccomp), to help make sure everything continues working correctly. That s it for v4.3. If I missed stuff you found interesting, please let me know! I m going to try to get more per-version posts out in time to catch up to v4.8, which appears to be tentatively scheduled for release this coming weekend.

2016, Kees Cook. This work is licensed under a Creative Commons Attribution-ShareAlike 3.0 License.
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Reproducible builds folks: Reproducible Builds: week 74 in Stretch cycle

Here is what happened in the Reproducible Builds effort between Sunday September 18 and Saturday September 24 2016: Outreachy We intend to participate in Outreachy Round 13 and look forward for new enthusiastic applications to contribute to reproducible builds. We're offering four different areas to work on: Reproducible Builds World summit #2 We are planning e a similar event to our Athens 2015 summit and expect to reveal more information soon. If you haven't been contacted yet but would like to attend, please contact holger. Toolchain development and fixes Mattia uploaded dpkg/1.18.10.0~reproducible1 to our experimental repository. and covered the details for the upload in a mailing list post. The most important change is the incorporation of improvements made by Guillem Jover (dpkg maintainer) to the .buildinfo generator. This is also in the hope that it will speed up the merge in the upstream. One of the other relevant changes from before is that .buildinfo files generated from binary-only builds will no longer include the hash of the .dsc file in Checksums-Sha256 as documented in the specification. Even if it was considered important to include a checksum of the source package in .buildinfo, storing it that way breaks other assumptions (eg. that Checksums-Sha256 contains only files part of that are part of a single upload, wheras the .dsc might not be part of that upload), thus we look forward for another solution to store the source checksum in .buildinfo. Bugs filed Reviews of unreproducible packages 250 package reviews have been added, 4 have been updated and 4 have been removed in this week, adding to our knowledge about identified issues. 4 issue types have been added: 3 issue types have been updated: Weekly QA work FTBFS bugs have been reported by: Documentation updates h01ger created a new Jenkins job so that every commit pushed to the master branch for the website will update reproducible-builds.org. diffoscope development strip-nondeterminism development reprotest development tests.reproducible-builds.org Misc. This week's edition was written by Chris Lamb, Holger Levsen and Mattia Rizzolo and reviewed by a bunch of Reproducible Builds folks on IRC.

25 September 2016

Vincent Sanders: I'll huff, and I'll puff, and I'll blow your house in

Sometimes it really helps to have a different view on a problem and after my recent writings on my Public Suffix List (PSL) library I was fortunate to receive a suggestion from my friend Enrico Zini.

I had asked for suggestions on reducing the size of the library further and Enrico simply suggested Huffman coding. This was a technique I had learned about long ago in connection with data compression and the intervening years had made all the details fuzzy which explains why it had not immediately sprung to mind.

A small subset of the Public Suffix List as stored within libnspslHuffman coding named for David A. Huffman is an algorithm that enables a representation of data which is very efficient. In a normal array of characters every character takes the same eight bits to represent which is the best we can do when any of the 256 values possible is equally likely. If your data is not evenly distributed this is not the case for example if the data was english text then the value is fifteen times more likely to be that for e than k.

every step of huffman encoding tree build for the example string tableSo if we have some data with a non uniform distribution of probabilities we need a way the data be encoded with fewer bits for the common values and more bits for the rarer values. To be efficient we would need some way of having variable length representations without storing the length separately. The term for this data representation is a prefix code and there are several ways to generate them.

Such is the influence of Huffman on the area of prefix codes they are often called Huffman codes even if they were not created using his algorithm. One can dream of becoming immortalised like this, to join the ranks of those whose names are given to units or whole ideas in a field must be immensely rewarding, however given Huffman invented his algorithm and proved it to be optimal to answer a question on a term paper in his early twenties I fear I may already be a bit too late.

The algorithm itself is relatively straightforward. First a frequency analysis is performed, a fancy way of saying count how many of each character is in the input data. Next a binary tree is created by using a priority queue initialised with the nodes sorted by frequency.

The resulting huffman tree and the binary representation of the input symbols
The two least frequent items count is summed together and a node placed in the tree with the two original entries as child nodes. This step is repeated until a single node exists with a count value equal to the length of the input.

To encode data once simply walks the tree outputting a 0 for a left node or 1 for right node until reaching the original value. This generates a mapping of values to bit output, the input is then simply converted value by value to the bit output. To decode the data the data is used bit by bit to walk the tree to arrive at values.

If we perform this algorithm on the example string table *!asiabvcomcoopitamazonawsarsaves-the-whalescomputebasilicata we can reduce the 488 bits (61 * 8 bit characters) to 282 bits or 40% reduction. Obviously in a real application the huffman tree would need to be stored which would probably exceed this saving but for larger data sets it is probable this technique would yield excellent results on this kind of data.

Once I proved this to myself I implemented the encoder within the existing conversion program. Although my perl encoder is not very efficient it can process the entire PSL string table (around six thousand labels using 40KB or so) in less than a second, so unless the table grows massively an inelegant approach will suffice.

The resulting bits were packed into 32bit values to improve decode performance (most systems prefer to deal with larger memory fetches less frequently) and resulted in 18KB of output or 47% of the original size. This is a great improvement in size and means the statically linked test program is now 59KB and is actually smaller than the gzipped source data.

$ ls -alh test_nspsl
-rwxr-xr-x 1 vince vince 59K Sep 25 23:58 test_nspsl
$ ls -al public_suffix_list.dat.gz 
-rw-r--r-- 1 vince vince 62K Sep  1 08:52 public_suffix_list.dat.gz

To be clear the statically linked program can determine if a domain is in the PSL with no additional heap allocations and includes the entire PSL ordered tree, the domain label string table and the huffman decode table to read it.

An unexpected side effect is that because the decode loop is small it sits in the processor cache. This appears to cause the string comparison function huffcasecmp() (which is not locale dependant because we know the data will be limited ASCII) performance to be close to using strcasecmp() indeed on ARM32 systems there is a very modest improvement in performance.

I think this is as much work as I am willing to put into this library but I am pleased to have achieved a result which is on par with the best of breed (libpsl still has a data representation 20KB smaller than libnspsl but requires additional libraries for additional functionality) and I got to (re)learn an important algorithm too.

20 September 2016

Vincent Sanders: If I see an ending, I can work backward.

Now while I am sure Arthur Miller was referring to writing a play when he said those words they have an oddly appropriate resonance for my topic.

In the early nineties Lou Montulli applied the idea of magic cookies to HTTP to make the web stateful, I imagine he had no idea of the issues he was going to introduce for the future. Like most of the web technology it was a solution to an immediate problem which it has never been possible to subsequently improve.

Chocolate chip cookie are much tastier than HTTP cookiesThe HTTP cookie is simply a way for a website to identify a connecting browser session so that state can be kept between retrieving pages. Due to shortcomings in the design of cookies and implementation details in browsers this has lead to a selection of unwanted side effects. The specific issue that I am talking about here is the supercookie where the super prefix in this context has similar connotations as to when applied to the word villain.

Whenever the browser requests a resource (web page, image, etc.) the server may return a cookie along with the resource that your browser remembers. The cookie has a domain name associated with it and when your browser requests additional resources if the cookie domain matches the requested resources domain name the cookie is sent along with the request.

As an example the first time you visit a page on www.example.foo.invalid you might receive a cookie with the domain example.foo.invalid so next time you visit a page on www.example.foo.invalid your browser will send the cookie along. Indeed it will also send it along for any page on another.example.foo.invalid

A supercookies is simply one where instead of being limited to one sub-domain (example.foo.invalid) the cookie is set for a top level domain (foo.invalid) so visiting any such domain (I used the invalid name in my examples but one could substitute com or co.uk) your web browser gives out the cookie. Hackers would love to be able to set up such cookies and potentially control and hijack many sites at a time.

This problem was noted early on and browsers were not allowed to set cookie domains with fewer than two parts so example.invalid or example.com were allowed but invalid or com on their own were not. This works fine for top level domains like .com, .org and .mil but not for countries where the domain registrar had rules about second levels like the uk domain (uk domains must have a second level like .co.uk).

NetSurf cookie manager showing a supercookieThere is no way to generate the correct set of top level domains with an algorithm so a database is required and is called the Public Suffix List (PSL). This database is a simple text formatted list with wildcard and inversion syntax and is at time of writing around 180Kb of text including comments which compresses down to 60Kb or so with deflate.

A few years ago with ICANN allowing the great expansion of top level domains the existing NetSurf supercookie handling was found to be wanting and I decided to implement a solution using the PSL. At this point in time the database was only 100Kb source or 40Kb compressed.

I started by looking at limited existing libraries. In fact only the regdom library was adequate but used 150Kb of heap to load the pre-processed list. This would have had the drawback of increasing NetSurf heap usage significantly (we still have users on 8Mb systems). Because of this and the need to run PHP script to generate the pre-processed input it was decided the library was not suitable.

Lacking other choices I came up with my own implementation which used a perl script to construct a tree of domains from the PSL in a static array with the label strings in a separate table. At the time my implementation added 70Kb of read only data which I thought reasonable and allowed for direct lookup of answers from the database.

This solution still required a pre-processing step to generate the C source code but perl is much more readily available, is a language already used by our tooling and we could always simply ship the generated file. As long as the generated file was updated at release time as we already do for our fallback SSL certificate root set this would be acceptable.

wireshark session shown NetSurf sending a co.uk supercookie to bbc.co.uk
I put the solution into NetSurf, was pleased no-one seemed to notice and moved on to other issues. Recently while fixing a completely unrelated issue in the display of session cookies in the management interface and I realised I had some test supercookies present in the display. After the initial "thats odd" I realised with horror there might be a deeper issue.

It quickly became evident the PSL generation was broken and had been for a long time, even worse somewhere along the line the "redundant" empty generated source file had been removed and the ancient fallback code path was all that had been used.

This issue had escalated somewhat from a trivial display problem. I took a moment to asses the situation a bit more broadly and came to the conclusion there were a number of interconnected causes, centered around the lack of automated testing, which could be solved by extracting the PSL handling into a "support" library.

NetSurf has several of these support libraries which could be used separately to the main browser project but are principally oriented towards it. These libraries are shipped and built in releases alongside the main browser codebase and mainly serve to make API more obvious and modular. In this case my main aim was to have the functionality segregated into a separate module which could be tested, updated and monitored directly by our CI system meaning the embarrassing failure I had found can never occur again.

Before creating my own library I did consider a library called libpsl had been created since I wrote my original implementation. Initially I was very interested in using this library given it managed a data representation within a mere 32Kb.

Unfortunately the library integrates a great deal of IDN and punycode handling which was not required in this use case. NetSurf already has to handle IDN and punycode translations and uses punycode encoded domain names internally only translating to unicode representations for display so duplicating this functionality using other libraries requires a great deal of resource above the raw data representation.

I put the library together based on the existing code generator Perl program and integrated the test set that comes along with the PSL. I was a little alarmed to discover that the PSL had almost doubled in size since the implementation was originally written and now the trivial test program of the library was weighing in at a hefty 120Kb.

This stemmed from two main causes:
  1. there were now many more domain label strings to be stored
  2. there now being many, many more nodes in the tree.
To address the first cause the length of the domain label strings was moved into the unused padding space within each tree node removing a byte from each domain label saving 6Kb. Next it occurred to me that while building the domain label string table that if the label to be added already existed as a substring within the table it could be elided.

The domain labels were sorted from longest to shortest and added in order searching for substring matches as the table was built this saved another 6Kb. I am sure there are ways to reduce this further I have missed (if you see them let me know!) but a 25% saving (47Kb to 35Kb) was a good start.

The second cause was a little harder to address. The structure representing nodes in the tree I started with was at first look reasonable.

struct pnode  
    uint16_t label_index; /* index into string table of label */
    uint16_t label_length; /* length of label */
    uint16_t child_node_index; /* index of first child node */
    uint16_t child_node_count; /* number of child nodes */
 ;

I examined the generated table and observed that the majority of nodes were leaf nodes (had no children) which makes sense given the type of data being represented. By allowing two types of node one for labels and a second for the child node information this would halve the node size in most cases and requiring only a modest change to the tree traversal code.

The only issue with this would be that a way to indicate a node has child information. It was realised that the domain labels can have a maximum length of 63 characters meaning their length can be represented in six bits so a uint16_t was excessive. The space was split into two uint8_t parts one for the length and one for a flag to indicate child data node followed.

union pnode  
    struct  
        uint16_t index; /* index into string table of label */
        uint8_t length; /* length of label */
        uint8_t has_children; /* the next table entry is a child node */
      label;
    struct  
        uint16_t node_index; /* index of first child node */
        uint16_t node_count; /* number of child nodes */
      child;
 ;

static const union pnode pnodes[8580] =  
    /* root entry */
      .label =   0, 0, 1    ,   .child =   2, 1553    ,
    /* entries 2 to 1794 */
      .label =  37, 2, 1    ,   .child =   1795, 6    ,

...

    /* entries 8577 to 8578 */
      .label =  31820, 6, 1    ,   .child =   8579, 1    ,
    /* entry 8579 */
      .label =  0, 1, 0    ,

 ;

This change reduced the node array size from 63Kb to 33Kb almost a 50% saving. I considered using bitfields to try and reduce the label length and has_children flag into a single byte but such packing will not reduce the length of a node below 32bits because it is unioned with the child structure.

A possibility of using the spare uint8_t derived by bitfield packing to store an additional label node in three other nodes was considered but added a great deal of complexity to node lookup and table construction for saving around 4Kb so was not incorporated.

With the changes incorporated the test program was a much more acceptable 75Kb reasonably close to the size of the compressed source but with the benefits of direct lookup. Integrating the libraries single API call into NetSurf was straightforward and resulted in correct operation when tested.

This episode just reminded me of the dangers of code that can fail silently. It exposed our users to a security problem that we thought had been addressed almost six years ago and squandered the limited resources of the project. Hopefully a lesson we will not have to learn again any time soon. If there is a positive to take away it is that the new implementation is more space efficient, automatically built and importantly tested

Michal Čihař: wlc 0.6

wlc 0.6, a command line utility for Weblate, has been just released. There have been some minor fixes, but the most important news is that Windows and OS X are now supported platforms as well. Full list of changes: wlc is built on API introduced in Weblate 2.6 and still being in development. Several commands from wlc will not work properly if executed against Weblate 2.6, first fully supported version is 2.7 (it is now running on both demo and hosting servers). You can usage examples in the wlc documentation.

Filed under: Debian English SUSE Weblate 0 comments

19 September 2016

Mike Gabriel: Rocrail changed License to some dodgy non-free non-License

The Background Story A year ago, or so, I took some time to search the internet for Free Software that can be used for controlling model railways via a computer. I was happy to find Rocrail [1] being one of only a few applications available on the market. And even more, I was very happy when I saw that it had been licensed under a Free Software license: GPL-3(+). A month ago, or so, I collected my old M rklin (Digital) stuff from my parents' place and started looking into it again after +15 years, together with my little son. Some weeks ago, I remembered Rocrail and thought... Hey, this software was GPLed code and absolutely suitable for uploading to Debian and/or Ubuntu. I searched for the Rocrail source code and figured out that it got hidden from the web some time in 2015 and that the license obviously has been changed to some non-free license (I could not figure out what license, though). This made me very sad! I thought I had found a piece of software that might be interesting for testing with my model railway. Whenever I stumble over some nice piece of Free Software that I plan to use (or even only play with), I upload this to Debian as one of the first steps. However, I highly attempt to stay away from non-free sofware, so Rocrail has become a no-option for me back in 2015. I should have moved on from here on... Instead... Proactively, I signed up with the Rocrail forum and asked the author(s) if they see any chance of re-licensing the Rocrail code under GPL (or any other FLOSS license) again [2]? When I encounter situations like this, I normally offer my expertise and help with such licensing stuff for free. My impression until here already was that something strange must have happened in the past, so that software developers choose GPL and later on stepped back from that decision and from then on have been hiding the source code from the web entirely. Going deeper... The Rocrail project's wiki states that anyone can request GitBlit access via the forum and obtain the source code via Git for local build purposes only. Nice! So, I asked for access to the project's Git repository, which I had been granted. Thanks for that. Trivial Source Code Investigation... So far so good. I investigated the source code (well, only the license meta stuff shipped with the source code...) and found that the main COPYING files (found at various locations in the source tree, containing a full version of the GPL-3 license) had been replaced by this text: 
Copyright (c) 2002 Robert Jan Versluis, Rocrail.net
All rights reserved.
Commercial usage needs permission.
The replacement happened with these Git commits: 
commit cfee35f3ae5973e97a3d4b178f20eb69a916203e
Author: Rob Versluis <r.j.versluis@rocrail.net>
Date:   Fri Jul 17 16:09:45 2015 +0200
    update copyrights
commit df399d9d4be05799d4ae27984746c8b600adb20b
Author: Rob Versluis <r.j.versluis@rocrail.net>
Date:   Wed Jul 8 14:49:12 2015 +0200
    update licence
commit 0daffa4b8d3dc13df95ef47e0bdd52e1c2c58443
Author: Rob Versluis <r.j.versluis@rocrail.net>
Date:   Wed Jul 8 10:17:13 2015 +0200
    update
Getting in touch again, still being really interested and wanting to help... As I consider such a non-license as really dangerous when distributing any sort of software, be it Free or non-free Software, I posted the below text on the Rocrail forum: 
Hi Rob,
I just stumbled over this post [3] [link reference adapted for this
blog post), which probably is the one you have referred to above.
It seems that Rocrail contains features that require a key or such
for permanent activation.  Basically, this is allowed and possible
even with the GPL-3+ (although Free Software activists will  not
appreciate that). As the GPL states that people can share the source
code, programmers can  easily deactivate license key checks (and
such) in the code and re-distribute that patchset as they  like.
Furthermore, the current COPYING file is really non-protective at
all. It does not really protect   you as copyright holder of the
code. Meaning, if people crash their trains with your software, you  
could actually be legally prosecuted for that. In theory. Or in the
U.S. ( ;-) ). Main reason for  having a long long license text is to
protect you as the author in case your software causes t trouble to
other people. You do not have any warranty disclaimer in your COPYING
file or elsewhere. Really not a good idea.
In that referenced post above, someone also writes about the nuisance
of license discussions in  this forum. I have seen various cases
where people produced software and did not really care for 
licensing. Some ended with a letter from a lawyer, some with some BIG
company using their code  under their copyright holdership and their
own commercial licensing scheme. This is not paranoia,  this is what
happens in the Free Software world from time to time.
A model that might be much more appropriate (and more protective to
you as the author), maybe, is a  dual release scheme for the code. A
possible approach could be to split Rocrail into two editions:  
Community Edition and Professional/Commercial Edition. The Community
Edition must be licensed in a  way that it allows re-using the code
in a closed-source, non-free version of Rocrail (e.g.   MIT/Expat
License or Apache2.0 License). Thus, the code base belonging to the
community edition  would be licensed, say..., as Apache-2.0 and for
the extra features in the Commercial Edition, you  may use any
non-free license you want (but please not that COPYING file you have
now, it really  does not protect your copyright holdership).
The reason for releasing (a reduced set of features of a) software as
Free Software is to extend  the user base. The honey jar effect, as
practise by many huge FLOSS projects (e.g. Owncloud,  GitLab, etc.).
If people could install Rocrail from the Debian / Ubuntu archives
directly, I am  sure that the user base of Rocrail will increase.
There may also be developers popping up showing  an interest in
Rocrail (e.g. like me). However, I know many FLOSS developers (e.g.
like me) that  won't waste their free time on working for a non-free
piece of software (without being paid).
If you follow (or want to follow) a business model with Rocrail, then
keep some interesting  features in the Commercial Edition and don't
ship that source code. People with deep interest may  opt for that.
Furthermore, another option could be dual licensing the code. As the
copyright holder of Rocrail  you are free to juggle with licenses and
apply any license to a release you want. For example, this  can be
interesing for a free-again Rocrail being shipped via Apple's iStore. 
Last but not least, as you ship the complete source code with all
previous changes as a Git project  to those who request GitBlit
access, it is possible to obtain all earlier versions of Rocrail. In 
the mail I received with my GitBlit credentials, there was some text
that  prohibits publishing the  code. Fine. But: (in theory) it is
not forbidden to share the code with a friend, for local usage.  This
friend finds the COPYING file, frowns and rewinds back to 2015 where
the license was still  GPL-3+. GPL-3+ code can be shared with anyone
and also published, so this friend could upload the  2015-version of
Rocrail to Github or such and start to work on a free fork. You also
may not want  this.
Thanks for working on this piece of software! It is highly
interesing, and I am still sad, that it  does not come with a free
license anymore. I won't continue this discussion and move on, unless
you  are interested in any of the above information and ask for more
expertise. Ping me here or directly  via mail, if needed. If the
expertise leads to parts of Rocrail becoming Free Software again, the 
expertise is offered free of charge ;-).
light+love
Mike
Wow, the first time I got moderated somewhere... What an experience! This experience now was really new. My post got immediately removed from the forum by the main author of Rocrail (with the forum's moderator's hat on). The new experience was: I got really angry when I discovererd having been moderated. Wow! Really a powerful emotion. No harassment in my words, no secrets disclosed, and still... my free speech got suppressed by someone. That feels intense! And it only occurred in the virtual realm, not face to face. Wow!!! I did not expect such intensity... The reason for wiping my post without any other communication was given as below and quite a statement to frown upon (this post has also been "moderately" removed from the forum thread [2] a bit later today): 
Mike,
I think its not a good idea to point out a way to get the sources back to the GPL periode.
Therefore I deleted your posting.
(The phpBB forum software also allows moderators to edit posts, so the critical passage could have been removed instead, but immediately wiping the full message, well...). Also, just wiping my post and not replying otherwise with some apology to suppress my words, really is a no-go. And the reason for wiping the rest of the text... Any Git user can easily figure out how to get a FLOSS version of Rocrail and continue to work on that from then on. Really. Now the political part of this blog post... Fortunately, I still live in an area of the world where the right of free speech is still present. I found out: I really don't like being moderated!!! Esp. if what I share / propose is really noooo secret at all. Anyone who knows how to use Git can come to the same conclusion as I have come to this morning. [Off-topic, not at all related to Rocrail: The last votes here in Germany indicate that some really stupid folks here yearn for another this time highly idiotic wind of change, where free speech may end up as a precious good.] To other (Debian) Package Maintainers and Railroad Enthusiasts... With this blog post I probably close the last option for Rocrail going FLOSS again. Personally, I think that gate was already closed before I got in touch. Now really moving on... Probably the best approach for my new train conductor hobby (as already recommended by the woman at my side some weeks back) is to leave the laptop lid closed when switching on the train control units. I should have listened to her much earlier. I have finally removed the Rocrail source code from my computer again without building and testing the application. I neither have shared the source code with anyone. Neither have I shared the Git URL with anyone. I really think that FLOSS enthusiasts should stay away from this software for now. For my part, I have lost my interest in this completely... References light+love,
Mike

13 September 2016

Dirk Eddelbuettel: anytime 0.0.1: New package for 'anything' to POSIXct (or Date)

anytime just arrived on CRAN as a very first release 0.0.1. So why (yet another) package dealing with dates and times? R excels at computing with dates, and times. By using typed representation we not only get all that functionality but also of the added safety stemming from proper representation. But there is a small nuisance cost: How often have we each told as.POSIXct() that the origin is epoch '1970-01-01'? Do we have to say it a million more times? Similarly, when parsing dates that are in some recogniseable form of the YYYYMMDD format, do we really have to manually convert from integer or numeric or factor or ordered to character first? Having one of several common separators and/or date / time month forms (YYYY-MM-DD, YYYY/MM/DD, YYYYMMDD, YYYY-mon-DD and so on, with or without times, with or without textual months and so on), do we really need a format string? anytime() aims to help as a small general purpose converter returning a proper POSIXct (or Date) object nomatter the input (provided it was somewhat parseable), relying on Boost date_time for the (efficient, performant) conversion. See some examples on the anytime page or the GitHub README.md, or in the screenshot below. And then just give it try! anytime examples For questions or comments use the issue tracker off the GitHub repo.

This post by Dirk Eddelbuettel originated on his Thinking inside the box blog. Please report excessive re-aggregation in third-party for-profit settings.

12 September 2016

Steve Kemp: If your code accepts URIs as input..

There are many online sites that accept reading input from remote locations. For example a site might try to extract all the text from a webpage, or show you the HTTP-headers a given server sends back in response to a request. If you run such a site you must make sure you validate the schema you're given - also remembering to do that if you're sent any HTTP-redirects.
Really the issue here is a confusion between URL & URI.
The only time I ever communicated with Aaron Swartz was unfortunately after his death, because I didn't make the connection. I randomly stumbled upon the html2text software he put together, which had an online demo containing a form for entering a location. I tried the obvious input: 
file:///etc/passwd
The software was vulnerable, read the file, and showed it to me. The site gives errors on all inputs now, so it cannot be used to demonstrate the problem, but on Friday I saw another site on Hacker News with the very same input-issue, and it reminded me that there's a very real class of security problems here. The site in question was http://fuckyeahmarkdown.com/ and allows you to enter a URL to convert to markdown - I found this via the hacker news submission. The following link shows the contents of /etc/hosts, and demonstrates the problem: http://fuckyeahmarkdown.example.com/go/?u=file:///etc/hosts&read=1&preview=1&showframe=0&submit=go The output looked like this: 
..
127.0.0.1 localhost
255.255.255.255 broadcasthost
::1 localhost
fe80::1%lo0 localhost
127.0.0.1 stage
127.0.0.1 files
127.0.0.1 brettt..
..
In the actual output of '/etc/passwd' all newlines had been stripped. (Which I now recognize as being an artifact of the markdown processing.) UPDATE: The problem is fixed now.

7 September 2016

Julian Andres Klode: New software: sicherboot

Fork me on GitHub Today, I wrote sicherboot, a tool to integrate systemd-boot into a Linux distribution in an entirely new way: With secure boot support. To be precise: The use case here is to only run trusted code which then unmounts an otherwise fully encrypted disk, as in my setup: screenshot-from-2016-09-06-04-09-52 If you want, sicherboot automatically creates db, KEK, and PK keys, and puts the public keys on your EFI System Partition (ESP) together with the KeyTool tool, so you can enroll the keys in UEFI. You can of course also use other keys, you just need to drop a db.crt and a db.key file into /etc/sicherboot/keys. It would be nice if sicherboot could enroll the keys directly in Linux, but there seems to be a bug in efitools preventing that at the moment. For some background: The Platform Key (PK) signs the Key Exchange Key (KEK) which signs the database key (db). The db key is the one signing binaries. sicherboot also handles installing new kernels to your ESP. For this, it combines the kernel with its initramfs into one executable UEFI image, and then signs that. Combined with a fully encrypted disk setup, this assures that only you can run UEFI binaries on the system, and attackers cannot boot any other operating system or modify parts of your operating system (except for, well, any block of your encrypted data, as XTS does not authenticate the data; but then you do have to know which blocks are which which is somewhat hard). sicherboot integrates with various parts of Debian: It can work together by dracut via an evil hack (diverting dracut s kernel/postinst.d config file, so we can run sicherboot after running dracut), it should support initramfs-tools (untested), and it also integrates with systemd upgrades via triggers on the /usr/lib/systemd/boot/efi directory. Currently sicherboot only supports Debian-style setups with /boot/vmlinuz-<version> and /boot/initrd.img-<version> files, it cannot automatically create combined boot images from or install boot loader entries for other naming schemes yet. Fixing that should be trivial though, with a configuration setting and some eval magic (or string substitution). Future planned features include: (1) support for multiple ESP partitions, so you can have a fallback partition on a different drive (think RAID type situation, keep one ESP on each drive, so you can remove a failing one); and (2) a tool to create a self-contained rescue disk image from a directory (which will act as initramfs) and a kernel (falling back to a vmlinuz file ) It might also be interesting to add support for other bootloaders and setups, so you could automatically sign a grub cryptodisk image for example. Not sure how much sense that makes. I published the source at https://github.com/julian-klode/sicherboot (MIT licensed) and uploaded the package to Debian, it should enter the NEW queue soon (or be in NEW by the time you read this). Give it a try, and let me know what you think.
Filed under: Debian, sicherboot

5 September 2016

Dirk Eddelbuettel: Rcpp 0.12.7: More updates

The seventh update in the 0.12.* series of Rcpp just arrived on the CRAN network for GNU R as well as in Debian. This 0.12.7 release follows the 0.12.0 release from late July, the 0.12.1 release in September, the 0.12.2 release in November, the 0.12.3 release in January, the 0.12.4 release in March, the 0.12.5 release in May, and the 0.12.6 release in July --- making it the eleventh release at the steady bi-montly release frequency. Keeping with the established pattern, this is again more of a maintenance release which addresses small bugs, nuisances or documentation issues without adding any major new features. One issue that got to a few people was our casual use of NORET in the definition of Rcpp::stop(). We had (ahem) overlooked that NORET is only defined by R 3.2.0 or later, and several folks trying to build on older releases of R (why?) got bitten. Well, at least we have a new record for most frequently reported bug ... Kidding aside, this is now fixed. Rcpp has become the most popular way of enhancing GNU R with C or C++ code. As of today, 759 packages on CRAN depend on Rcpp for making analytical code go faster and further. That is up by well over fifty packages since the last release in mid-July! We are once again fortunate to have a number of pull request, from first-timers to regulars. James "coatless" Balamuta in particular relentlessly pushed for better documentation and cleanup of numerous dangling issue tickets. Artem Klevtsov also contributed again. Qiang, Kevin and I also got some changes in for the Rcpp Core team. More details are again below.
Changes in Rcpp version 0.12.7 (2016-09-04)
  • Changes in Rcpp API:
    • The NORET macro is now defined if it was not already defined by R itself (Kevin fixing issue #512).
    • Environment functions get() & find() now accept a Symbol (James Balamuta in #513 addressing issue #326).
    • Several uses of Rf_eval were replaced by the preferred Rcpp::Rcpp_eval (Qiang in PR #523 closing #498).
    • Improved Autogeneration Warning for RcppExports (James Balamuta in #528 addressing issue #526).
    • Fixed invalid C++ prefix identifiers in auto-generated code (James Balamuta in #528 and #531 addressing issue #387; Simon Dirmeier in #548).
    • String constructors now set default UTF-8 encoding (Qiang Kou in #529 fixing #263).
    • Add variadic variants of the RCPP_RETURN_VECTOR and RCPP_RETURN_MATRIX macro when C++11 compiler used (Artem Klevtsov in #537 fixing #38).
  • Changes in Rcpp build system
    • Travis CI is now driven via run.sh from our fork, and deploys all packages as .deb binaries using our PPA where needed (Dirk in #540 addressing issue #517).
  • Changes in Rcpp unit tests
    • New unit tests for random number generators the R namespace which call the standalone Rmath library. (James Balamuta in #514 addressing issue #28).
  • Changes in Rcpp Examples:
    • Examples that used cxxfunction() from the inline package have been rewritten to use either sourceCpp() or cppFunction() (James Balamuta in #541, #535, #534, and #532 addressing issue #56).
Thanks to CRANberries, you can also look at a diff to the previous release. As always, even fuller details are on the Rcpp Changelog page and the Rcpp page which also leads to the downloads page, the browseable doxygen docs and zip files of doxygen output for the standard formats. A local directory has source and documentation too. Questions, comments etc should go to the rcpp-devel mailing list off the R-Forge page.

This post by Dirk Eddelbuettel originated on his Thinking inside the box blog. Please report excessive re-aggregation in third-party for-profit settings.

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