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Message-ID: <1474222407.2428.2.camel@decadent.org.uk>
Subject: Re: [PATCH 2/9] exec: turn self_exec_id into self_privunit_id
From: Ben Hutchings <ben@decadent.org.uk>
To: Jann Horn <jann@thejh.net>,
        Alexander Viro <viro@zeniv.linux.org.uk>,
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        Thomas Gleixner <tglx@linutronix.de>,
        Benjamin LaHaise <bcrl@kvack.org>
Cc: linux-fsdevel@vger.kernel.org,
        linux-security-module@vger.kernel.org, security@kernel.org
Date: Sun, 18 Sep 2016 19:13:27 +0100
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On Sun, 2016-09-18 at 17:05 +0200, Jann Horn wrote:
> This ensures that self_privunit_id ("privilege unit ID") is only shared b=
y
> processes that share the mm_struct and the signal_struct; not just
> spatially, but also temporally. In other words, if you do execve() or
> clone() without CLONE_THREAD, you get a new privunit_id that has never be=
en
> used before.
[...]
> +void increment_privunit_counter(void)
> +{
> +	BUILD_BUG_ON(NR_CPUS > (1 << 16));
> +	current->self_privunit_id =3D this_cpu_add_return(exec_counter, NR_CPUS=
);
> +}
[...]

This will wrap incorrectly if NR_CPUS is not a power of 2 (which is
unusual but allowed).

Ben.
=C2=A0
--=20
Ben Hutchings
Klipstein's 4th Law of Prototyping and Production:
=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=
=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=
=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0A fail-sa=
fe circuit will destroy
others.

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