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

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Message-ID: <CAGXu5jKNWMYnTdh-t2C9gG2PL+frRSOY=O5hyuHmN2uyQ3YFbg@mail.gmail.com>
Date:	Wed, 11 Jan 2012 14:41:09 -0800
From:	Kees Cook <keescook@...omium.org>
To:	Andrew Morton <akpm@...ux-foundation.org>
Cc:	Xiaotian Feng <xtfeng@...il.com>, linux-kernel@...r.kernel.org,
	Xiaotian Feng <dannyfeng@...cent.com>,
	Al Viro <viro@...iv.linux.org.uk>,
	Vasiliy Kulikov <segoon@...nwall.com>,
	Stephen Wilson <wilsons@...rt.ca>,
	David Rientjes <rientjes@...gle.com>
Subject: Re: [PATCH] proc: fix null pointer deref in proc_pid_permission()

On Wed, Jan 11, 2012 at 1:58 PM, Andrew Morton
<akpm@...ux-foundation.org> wrote:
> On Wed, 11 Jan 2012 12:43:30 -0800
> Kees Cook <keescook@...omium.org> wrote:
>> On Wed, Jan 11, 2012 at 01:47:05PM -0500, 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.
>>
>> Nice catch!
>>
>> However since this error is returned to userspace, shouldn't this be
>> -ENOENT instead?
>
> Failed get_proc_task() frequently results in -ESRCH.  And less
> frequently results in -ENOENT.
>
> It seems odd that inode_operations.permission() would ever return
> anything other than zero or -EPERM.

Right, but won't this show up at ESRCH from open(2)? If this is used
as-is, we just need to have the manpages updated.

-Kees

-- 
Kees Cook
ChromeOS Security
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