Re: [musl] vfork()-based posix_spawn() has more failure modes than fork()-based one

[Alexey Izbyshev <izbyshev@ispras.ru>]

On 2022-05-03 00:31, Carlos O'Donell wrote:
> On 5/2/22 17:25, Florian Weimer wrote:
>> * Rich Felker:
>> 
>>> I'm trying to understand how this comes to be. The child should
>>> inherit the namespaces of the parent and thus should not be in a
>>> different namespace that precludes spawn. I'm guessing this is some
>>> oddity where unshare doesn't affect the process itself, only its
>>> children? If so, it seems like a bug that it doesn't affect the
>>> process itself after execve (after unshare(1) runs your test 
>>> program),
>>> but that probably can't be fixed now on the Linux side for stability
>>> reasons. :(
>> 
>> It's about fundamentally conflicting requirements.
>> 
>> The vDSO data mapping needs to store the time offset, so it has to be
>> distinct from the original namespace.  vfork preserves the VM sharing.
>> It's not possible to do both things at the same time.
>> 
>> unshare(CLONE_NEWTIME) should have been specified to only take effect
>> after execve, when the vDSO is remapped anyway.
> 
> Can we ask some kernel developers for an opinion?

Christian Brauner had some comments [1,2] on this. Time namespaces were 
added in [3] by Andrei Vagin. Adding both to CC.

Alexey

[1] https://bugzilla.kernel.org/show_bug.cgi?id=215769#c6
[2] https://bugzilla.kernel.org/show_bug.cgi?id=215769#c10
[3] 
https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=769071ac9f20b6a447410c7eaa55d1a5233ef40c