linux-kernel - Re: [PATCH] proc: fix null pointer deref in proc_pid

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Message-ID: <alpine.DEB.2.00.1201111348380.21755@chino.kir.corp.google.com>
Date:	Wed, 11 Jan 2012 13:49:19 -0800 (PST)
From:	David Rientjes <rientjes@...gle.com>
To:	Xiaotian Feng <xtfeng@...il.com>
cc:	linux-kernel@...r.kernel.org,
	Xiaotian Feng <dannyfeng@...cent.com>,
	Al Viro <viro@...iv.linux.org.uk>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Vasiliy Kulikov <segoon@...nwall.com>,
	Stephen Wilson <wilsons@...rt.ca>
Subject: Re: [PATCH] proc: fix null pointer deref in proc_pid_permission()

On Wed, 11 Jan 2012, Xiaotian Feng wrote:

> get_proc_task() can fail to search the task and return NULL, put_task_struct()
> will then bomb the kernel with following oops:
> 
> [ 1870.574045] BUG: unable to handle kernel NULL pointer dereference at 0000000000000010
> [ 1870.574065] IP: [<ffffffff81217d34>] proc_pid_permission+0x64/0xe0
> [ 1870.574088] PGD 112075067 PUD 112814067 PMD 0
> [ 1870.574106] Oops: 0002 [#1] PREEMPT SMP
> 
> This is a regression introduced by commit 0499680a, kernel should
> return -ESRCH if get_proc_task() failed.
> 
> Signed-off-by: Xiaotian Feng <dannyfeng@...cent.com>
> Cc: Al Viro <viro@...iv.linux.org.uk>
> Cc: Andrew Morton <akpm@...ux-foundation.org>
> Cc: Vasiliy Kulikov <segoon@...nwall.com>
> Cc: Stephen Wilson <wilsons@...rt.ca>
> Cc: David Rientjes <rientjes@...gle.com>

Acked-by: David Rientjes <rientjes@...gle.com>

You're right to use -ESRCH so it matches the same behavior as the 
remainder of /proc/pid when get_proc_task() returns NULL.
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