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

[Alexey Izbyshev <izbyshev@ispras.ru>]

On 2022-05-03 00:49, Alexey Izbyshev wrote:
> 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.
> 
(Trying a different email for Andrei Vagin)

> 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