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Message-ID: <b8e0886a06f2e28ca3ddad277fa09a34@ispras.ru>
Date: Tue, 03 May 2022 00:49:16 +0300
From: Alexey Izbyshev <izbyshev@...ras.ru>
To: musl@...ts.openwall.com
Cc: Florian Weimer <fweimer@...hat.com>, Rich Felker <dalias@...c.org>,
Andrei Vagin <avagin@...nvz.org>, Christian Brauner <brauner@...nel.org>
Subject: Re: vfork()-based posix_spawn() has more failure modes than
fork()-based one
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
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