linux-kernel - Re: [PATCH] syscalls: Document OCI seccomp filter interactions & workaround

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Date:   Tue, 24 Nov 2020 19:09:44 +0100
From:   Florian Weimer <fweimer@...hat.com>
To:     Mark Wielaard <mark@...mp.org>
Cc:     Christian Brauner <christian.brauner@...ntu.com>,
        linux-api@...r.kernel.org, linux-doc@...r.kernel.org,
        linux-kernel@...r.kernel.org, dev@...ncontainers.org,
        corbet@....net, Carlos O'Donell <carlos@...hat.com>
Subject: Re: [PATCH] syscalls: Document OCI seccomp filter interactions &
 workaround

* Mark Wielaard:

> For valgrind the issue is statx which we try to use before falling back
> to stat64, fstatat or stat (depending on architecture, not all define
> all of these). The problem with these fallbacks is that under some
> containers (libseccomp versions) they might return EPERM instead of
> ENOSYS. This causes really obscure errors that are really hard to
> diagnose.

The probing sequence I proposed should also work for statx. 8-p

> Don't you have the same issue with glibc for those architectures that
> don't have fstatat or 32bit arches that need 64-bit time_t? And if so,
> how are you working around containers possibly returning EPERM instead
> of ENOSYS?

That's a good point.  I don't think many people run 32-bit containers in
the cloud.  The Y2038 changes in glibc impact 64-bit ports a little, but
mostly on the fringes (e.g., clock_nanosleep vs nanosleep).

Thanks,
Florian
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