Libseccomp 2.4.0 Released

It's been over a year since the last libseccomp release (libseccomp v2.3.3 was released on January 10, 2018) but I'm happy to announce that today we've released libseccomp v2.4.0!

The libseccomp v2.4.0 release is a drop-in replacement for previous v2.x releases; no recompilation of applications is required. Although applications will need to be restarted to take advantage of the new libseccomp release.

The new release is a significant upgrade over libseccomp v2.3.3. In addition to a number of new features, there was a big push to improve the quality of the code in this release; a lot of time was spent adding new tests and fixing bugs. In fact there is one bug in particular that is worth giving specific mention: prior to the v2.4.0 release, libseccomp's 64-bit syscall argument comparison code was incorrect and generated seccomp-bpf filters that would not always correctly match on syscall arguments. The impact of this bug should be relatively limited, but the researcher who identified this bug, Jann Horn, was able to identify libseccomp filters in systemd and Tor that were incorrectly generated due to this bug. Jann did not find any other vulnerable applications, but it is possible other applications are affected.

I would like to thank researches like Jann Horn who help identify problems in security critical applications and libraries like libseccomp, as well as the 46 people who have contributed their time, effort, code, and artwork to libseccomp (the complete list can be found in the CREDITS file) - thank you!

Changes in the v2.4.0 release include:

  • Update the syscall table for Linux v5.0-rc5
  • Added support for the SCMP_ACT_KILL_PROCESS action
  • Added support for the SCMP_ACT_LOG action and SCMP_FLTATR_CTL_LOG attribute
  • Added explicit 32-bit (SCMP_AX_32(...)) and 64-bit (SCMP_AX_64(...)) argument comparison macros to help protect against unexpected sign extension
  • Added support for the parisc and parisc64 architectures
  • Added the ability to query and set the libseccomp API level via seccomp_api_get(3) and seccomp_api_set(3)
  • Return -EDOM on an endian mismatch when adding an architecture to a filter
  • Renumber the pseudo syscall number for subpage_prot() so it no longer conflicts with spu_run()
  • Fix PFC generation when a syscall is prioritized, but no rule exists
  • Numerous fixes to the seccomp-bpf filter generation code
  • Switch our internal hashing function to jhash/Lookup3 to MurmurHash3
  • Numerous tests added to the included test suite, coverage now at ~92%
  • Update our Travis CI configuration to use Ubuntu 16.04
  • Numerous documentation fixes and updates

Linux 5.0 Released

Instead of Linux v4.21, Linux v5.0 was released on March 3, 2019. The major version bump doesn't reflect any major changes, other than there were a "lot" of v4.x releases and Linus decided it was time to increment the major version number.

The SELinux and audit kernel highlights are below.


  • Rework the internal SELinux label database (sidtab) to improve both availability during policy reloads and lookup performance. This should generally improve SELinux performance as well as reduce SELinux related ENOMEM errors during a policy reload.

  • The SELinux filesystem mount controls have changed to always allow filesystem submounts. For all current in-tree filesystems, granting permission to mount submounts should not degrade the security of the system, and brings the SELinux access controls more in line with the kernel's capability checks for submounts. As Ondrej Mosnacek explains in the patch description:

    ... In the current kernel tree, the MS_SUBMOUNT flag is set only via vfs_submount(), which is called only from the following places:
    - AFS, when automounting special "symlinks" referencing other cells
    - CIFS, when automounting "referrals"
    - NFS, when automounting subtrees
    - debugfs, when automounting tracefs

    In all cases the submounts are meant to be transparent to the user and it makes sense that if mounting the master is allowed, then so should be the automounts. Note that CAP_SYS_ADMIN capability checking is already skipped for (SB_KERNMOUNT|SB_SUBMOUNT) ...

  • Internal kernel changes to support the internal VFS mount API changes. These changes should have no impact on the SELinux policy or user experience.

  • A number of internal kernel bug fixes relating to error handling and policy byte ordering.


  • System call auditing support was added to the RISC-V architecture.

  • The file capabilities fields, the "cap_f*" fields in the PATH record, have been shortened to log only a value of "0" when none of the capabilities are set. This should help shorten PATH records on systems that don't make use of file capabilities.

  • Fixed a problem where empty arguments were not being properly logged in the EXECVE record.

  • A large number of fixes to the audit subsystem's use of fsnotify. This should help improve the performance and robustness of audit's filesystem watches.

  • Removed the CONFIG_AUDIT_WATCH and CONFIG_AUDIT_TREE kernel configuration options, using the CONFIG_AUDITSYSCALL option instead, and forcing the CONFIG_FSNOTIFY option when CONFIG_AUDITSYSCALL is enabled.

  • A number of internal code cleanups.

Linux 4.20 Released

Linux v4.20 was released on December 23, 2018. Not only is this release the last release of 2018, it is believed to be the last Linux v4.x release, with the next Linux release expected to be v5.0.

This release was a relatively small release from a SELinux perspective, and an even smaller release from an audit point of view, with no audit related changes between Linux v4.19 and v4.20.


  • When we added support for cgroup2 file labeling in Linux v4.14 we unfortunately broke mounting of cgroup2 filesystems on older SELinux policies which were missing a genfscon rule for cgroup2. We've fixed this problem by marking the cgroup2 files as unlabeled when there is no genfscon rule.

  • Add additional address length checks to the SELinux SCTP code to ensure properly handle malformed user input during bind() and connect().

  • Improved validation of the MLS field to catch invalid SELinux labels. This also resulted in a number of code simplifications.

  • Added SELinux netlink definitions for RTM_NEWCHAIN, RTM_DELCHAIN, and RTM_GETCHAIN.

  • Internal improvements caught by syzbot as well as some minor LSM infrastructure changes.