On 11/07/2017 09:35 PM, Michael Kerrisk (man-pages) wrote:
This change broke my code that was doing seccomp filtering for the open() system call number (__NR_open). The breakage in question is not serious, since this was really just demonstration code. However, I want to raise awareness that these sorts of changes have the potential to possibly cause breakages for some code using seccomp, and note that I think such changes should not be made lightly or gratuitously.
I have the opposite view: We should make such changes as often as possible, to remind people that seccomp filters (and certain SELinux and AppArmor policies) are incompatible with the GNU/Linux model, where everything is developed separately and not maintained within a single source tree (unlike say OpenBSD). This means that you really can't deviate from the upstream Linux userspace ABI (in the broadest possible sense) and still expect things to work.
I know that people like to slap seccomp filters on everything today, but without careful examination, that is likely to introduce bugs (particularly on rarely used code paths). It can also cause the process to switch to legacy interfaces with known issues (e.g., reading from /dev/urandom instead of getrandom, without waiting for the kernel to signal initialization of the pool).
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