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Re: kernel: tmpfs use-after-free
From: Kurt Seifried <kseifried () redhat com>
Date: Mon, 25 Feb 2013 14:26:09 -0700

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On 02/25/2013 12:50 PM, Jason A. Donenfeld wrote:
Hey all,

While everyone's going wild hndl->dump'ing with CVE-2013-1763,
there's apparently been another silent security fix with 
5f00110f7273f9ff04ac69a5f85bb535a4fd0987 [1]:

tmpfs: fix use-after-free of mempolicy object

The tmpfs remount logic preserves filesystem mempolicy if the
mpol=M option is not specified in the remount request.  A new
policy can be specified if mpol=M is given.

Before this patch remounting an mpol bound tmpfs without
specifying mpol= mount option in the remount request would set
the filesystem's mempolicy object to a freed mempolicy object.

How far back does this issue go? I see it in both 2.6.36 and 3.3.
I did not look back further.


The commit message goes on with details on how to trigger it. Note 
that as of 5eaf563e53294d6696e651466697eb9d491f3946 [2], you can
now mount filesystems as an unprivileged user after a call to 
unshare(CLONE_NEWUSER | CLONE_NEWNS), or a similar clone(2) call.
This means all those random random filesystem bugs you have laying
around in the junk bin are now quite useful. ++tricks;

Cheers, Jason


[1]
http://git.zx2c4.com/linux/commit/?id=5f00110f7273f9ff04ac69a5f85bb535a4fd0987


[2]
http://git.zx2c4.com/linux/commit/?id=5eaf563e53294d6696e651466697eb9d491f3946

-- Jason A. Donenfeld www.zx2c4.com


Please use CVE-2013-1767 for this issue.

- -- 
Kurt Seifried Red Hat Security Response Team (SRT)
PGP: 0x5E267993 A90B F995 7350 148F 66BF 7554 160D 4553 5E26 7993

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