Re: Semantics of SECCOMP_MODE_STRICT?

Aleksa Sarai
2021-06-30T05:13:17Z

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On 2021-06-29, Eric W. Biederman <ebiederm@xmission.com> wrote:
>
> I am the process of cleaning up the process exit path in the kernel, and
> as part of that I am looking at the callers of do_exit. A very
> interesting one is __seccure_computing_strict.
>
> Looking at the code is very clear that if a system call is attempted
> that is not in the table the thread attempting to execute that system
> call is terminated.
>
> Reading the man page for seccomp it says that the process is delivered
> SIGKILL.
>
> The practical difference is what happens for multi-threaded
> applications.
>
> What are the desired semantics for a multi-threaded application if one
> thread attempts to use a unsupported system call? Should the thread be
> terminated or the entire application?
>
> Do we need to fix the kernel, or do we need to fix the manpages?

My expectation is that the correct action should be the equivalent of
SECCOMP_RET_KILL(_THREAD) which kills the thread and is the current
behaviour (SECCOMP_RET_KILL_PROCESS is relatively speaking quite new).

--
Aleksa Sarai
Senior Software Engineer (Containers)
SUSE Linux GmbH
<https://www.cyphar.com/>

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