oss-security - Linux: packet: fix races in fanout

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Message-ID: <20170228162524.47jesr3zopycriir@eldamar.local>
Date: Tue, 28 Feb 2017 17:25:24 +0100
From: Salvatore Bonaccorso <carnil@...ian.org>
To: OSS Security Mailinglist <oss-security@...ts.openwall.com>
Subject: Linux: packet: fix races in fanout_add() (CVE-2017-6346)

Hi

CVE-2017-6346 was assigned by MITRE to the following (via
https://cveform.mitre.org/):

https://git.kernel.org/linus/d199fab63c11998a602205f7ee7ff7c05c97164b

> packet: fix races in fanout_add()
> 
> Multiple threads can call fanout_add() at the same time.
> 
> We need to grab fanout_mutex earlier to avoid races that could
> lead to one thread freeing po->rollover that was set by another thread.
> 
> Do the same in fanout_release(), for peace of mind, and to help us
> finding lockdep issues earlier.

Since 4.2 the races can lead to a use-after-free.

The fix was backported to 4.9.13 as well.

Regards,
Salvatore

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