linux-kernel - Re: c/r: broken locking when executing map

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Date:	Sat, 5 May 2012 22:20:51 +0400
From:	Vasiliy Kulikov <segoon@...nwall.com>
To:	Cyrill Gorcunov <gorcunov@...nvz.org>
Cc:	Sasha Levin <levinsasha928@...il.com>, khlebnikov@...nvz.org,
	xemul@...allels.com, Dave Jones <davej@...hat.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Andrew Morton <akpm@...ux-foundation.org>
Subject: Re: c/r: broken locking when executing map_files

Hi Cyrill,

On Thu, May 03, 2012 at 21:31 +0400, Cyrill Gorcunov wrote:
> On Wed, May 02, 2012 at 09:27:56PM +0400, Cyrill Gorcunov wrote:
> > > 
> > > My theory is that files under map_files shouldn't be executable,
> > > but since I'm not sure what the usermode code for c/r does exactly,
> > > I should probably confirm that first. If it's indeed the case, you
> > > can probably skip the rest of this mail.
> > 
> > Thanks Sasha, I'll take a look!
> 
> Sasha, the patch below should fix the lock problem (still I would
> prefer to obtain confirm on patch from Vasiliy, CC'ed).
...
> ---
>  fs/proc/base.c |    8 +++-----
>  1 file changed, 3 insertions(+), 5 deletions(-)
> 
> Index: linux-2.6.git/fs/proc/base.c
> ===================================================================
> --- linux-2.6.git.orig/fs/proc/base.c
> +++ linux-2.6.git/fs/proc/base.c
> @@ -2226,16 +2226,16 @@ static struct dentry *proc_map_files_loo
>  		goto out;
>  
>  	result = ERR_PTR(-EACCES);
> -	if (lock_trace(task))
> +	if (!ptrace_may_access(task, PTRACE_MODE_READ))

Probably it will be better to change mutex_lock_killable() to
mutex_lock_killable_nested() inside of lock_trace() instead of this change?
It would keep the race-free check.

Thanks,

-- 
Vasily Kulikov
http://www.openwall.com - bringing security into open computing environments
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