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Message-ID: <5e002596-2450-98e0-f06b-39c458dcaf71@redhat.com>
Date: Mon, 2 May 2022 17:31:53 -0400
From: Carlos O'Donell <carlos@...hat.com>
To: musl@...ts.openwall.com, Florian Weimer <fweimer@...hat.com>,
Rich Felker <dalias@...c.org>
Cc: Alexey Izbyshev <izbyshev@...ras.ru>
Subject: Re: vfork()-based posix_spawn() has more failure modes than
fork()-based one
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?
--
Cheers,
Carlos.
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