Seccomp implications for glibc wrapper function changes

[Michael Kerrisk (man-pages)]

Hi Florian,

On 8 November 2017 at 07:24, Florian Weimer <fweimer@redhat.com> wrote:
> 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).

Thanks. The above is a good summary of the counterpoints to my initial argument.

Cheers,

Michael

-- 
Michael Kerrisk
Linux man-pages maintainer; http://www.kernel.org/doc/man-pages/
Linux/UNIX System Programming Training: http://man7.org/training/