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

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Date:	Wed, 22 Aug 2012 21:49:35 +0000
From:	halfdog <me@...fdog.net>
To:	kirill.shutemov@...ux.intel.com,
	Alexander Viro <viro@...iv.linux.org.uk>
CC:	"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

Got a hint via IRC, that I should not send patch idea for review to
"generic" list, but to maintainers and last (or relevant) comitters of code.

http://git.kernel.org/?p=linux/kernel/git/stable/linux-stable.git;a=commitdiff;h=bf2a9a39639b8b51377905397a5005f444e9a892

CC to generic just for the records

halfdog wrote:
> 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
> 
> 

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