linux-kernel - Re: Search for patch for kernel stack data disclosure in binfmt

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Date:	Sun, 19 Aug 2012 08:39:57 +0000
From:	halfdog <me@...fdog.net>
To:	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: Search for patch for kernel stack data disclosure in binfmt_script
 during execve

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halfdog wrote:
> I'm searching for a patch for linux kernel stack disclosure in 
> binfmt_script with crafted interpreter names when CONFIG_MODULES
> is active (see [1]).

Please disregard my previous proposal [2], since it did not address
the problem directly (referencing local stack frame data from bprm
structure) but worked around it. I suspect, that this could increase
probability to reintroduce similar bugs.

Opinions on (untested sketch for) second solution: Could someone look
on the source code comments and changes in patch to judge, if this is
going in the right direction?

Explanation of patch: Since load_script will start to irreversibly
change bprm structures at some point (using stack local data was one
of those changes), try to delay this point. Run checks if load_script
could be the right handler, if not give other binfmt handlers the
chance to do so.

If binfmt_script is the right one, try to load the interpreter
(causing bprm modification), if failing make sure that no other binfmt
handler has the chance to continue on the now modified bprm data.

CAVEAT: This assumes, that if binfmt_script could handle the load,
that it would be the one and only binfmt with that ability, so no
other one, e.g. binfmt_misc should have the chance to do so. If this
assumption is wrong, leaving binfmt_script would have to rollback all
bprm changes (e.g. restore old credentials).

hd

[1]
http://www.halfdog.net/Security/2012/LinuxKernelBinfmtScriptStackDataDisclosure/
[2] http://lkml.org/lkml/2012/8/18/75

- -- 
http://www.halfdog.net/
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