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Message-ID: <20210129164208.GA8779@openwall.com>
Date: Fri, 29 Jan 2021 17:42:08 +0100
From: Solar Designer <solar@...nwall.com>
To: oss-security@...ts.openwall.com
Subject: Re: Linux Kernel: local priv escalation via futexes
Hi,
I'm not familiar with futexes, but just to save others a few minutes on
looking this up:
On Fri, Jan 29, 2021 at 11:09:28AM +0100, Marcus Meissner wrote:
> - Address a longstanding issue where the user space part of the PI
> futex is not writeable. The kernel returns with inconsistent state
> which can in the worst case result in a UAF of a tasks kernel
> stack.
>
> The solution is to establish consistent kernel state which makes
> future operations on the futex fail because user space and kernel
> space state are inconsistent. Not a problem as PI futexes
> fundamentaly require a functional RW mapping and if user space
> pulls the rug under it, then it can keep the pieces it asked for.
> * tag 'locking-urgent-2021-01-28' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip:
> futex: Handle faults correctly for PI futexes
FWIW, this commit has:
Fixes: 1b7558e457ed ("futexes: fix fault handling in futex_lock_pi")
and that other commit is from 2008. So probably all currently
maintained Linux distros and deployments are affected, unless something
else mitigated the issue in some kernel versions.
Alexander
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