linux-kernel - Re: [PATCH] kernel/kmod: fix use-after-free of the sub

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Message-ID: <20141017090214.24eeef30@mschwide>
Date:	Fri, 17 Oct 2014 09:02:14 +0200
From:	Martin Schwidefsky <schwidefsky@...ibm.com>
To:	Tetsuo Handa <penguin-kernel@...ove.SAKURA.ne.jp>
Cc:	oleg@...hat.com, linux-kernel@...r.kernel.org,
	torvalds@...ux-foundation.org, akpm@...ux-foundation.org
Subject: Re: [PATCH] kernel/kmod: fix use-after-free of the
 sub_infostructure

On Fri, 17 Oct 2014 06:30:29 +0900
Tetsuo Handa <penguin-kernel@...ove.SAKURA.ne.jp> wrote:

> Regarding UMH_NO_WAIT, the sub_info structure can be freed by
> __call_usermodehelper() before the worker thread returns from
> do_execve(), allowing memory corruption when do_execve() failed
> after exec_mmap() is called.
> 
> Regarding UMH_WAIT_EXEC, the call to umh_complete() allows
> call_usermodehelper_exec() to continue which then frees sub_info.
> 
> To fix this race, we need to make sure that the call to
> call_usermodehelper_freeinfo() in call_usermodehelper_exec() is
> always made after the last store to sub_info->retval.

I like this improved description for the UMH_NO_WAIT and UMH_WAIT_EXEC
cases. I mix it with parts of the original description. 

-- 
blue skies,
   Martin.

"Reality continues to ruin my life." - Calvin.

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