[Bug libc/29115] vfork()-based posix_spawn() has more failure modes than fork()-based one

["carlos at redhat dot com" <sourceware-bugzilla@sourceware.org>]

https://sourceware.org/bugzilla/show_bug.cgi?id=29115

Carlos O'Donell <carlos at redhat dot com> changed:

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                 CC|                            |carlos at redhat dot com

--- Comment #5 from Carlos O'Donell <carlos at redhat dot com> ---
Either the kernel supports vfork or it doesn't.

A time namespace, or a seccomp filter are all the same problems, and we should
return the error the userspace.

Adding code which will only be exercised in the event that a time namespace is
in use is going to result in increased long-term maintenance costs.

It also results in unexpected surprise behaviour when the developer runs under
a time namespace e.g. more memory usage, different code paths taken etc.

Rather than add long-term maintenance and surprise developers my suggestion is
to fail the posix_spawn.

Users can take this up with the kernel to add support for vfork in time
namespaces, or with their sandboxing technology provider.

There might be exceptional cases where we need to add fallbacks, but I can't
see that this is one of those cases. For example clone3 to clone2 fallback is
sensible.

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