linux-kernel - Re: [PATCH] fork.c: fix NULL pointer dereference when nr

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Message-ID: <alpine.LRH.1.10.0902070006370.18789@tundra.namei.org>
Date:	Sat, 7 Feb 2009 00:06:56 +1100 (EST)
From:	James Morris <jmorris@...ei.org>
To:	David Howells <dhowells@...hat.com>
cc:	torvalds@...l.org, akpm@...ux-foundation.org,
	linux-kernel@...r.kernel.org, linux-security-module@...r.kernel.org
Subject: Re: [PATCH] fork.c: fix NULL pointer dereference when nr_threads ==
 threads-max

On Fri, 6 Feb 2009, David Howells wrote:

> From: Li Zefan <lizf@...fujitsu.com>
> 
> I happened to forked lots of processes, and hit NULL pointer dereference.
> It is because in copy_process() after checking max_threads, 0 is returned
> but not -EAGAIN.
> 
> The bug is introduced by this patch:
> 
> | commit f1752eec6145c97163dbce62d17cf5d928e28a27
> | Author: David Howells <dhowells@...hat.com>
> | Date:   Fri Nov 14 10:39:17 2008 +1100
> |
> |    CRED: Detach the credentials from task_struct
> 
> Signed-off-by: Li Zefan <lizf@...fujitsu.com>
> Signed-off-by: David Howells <dhowells@...hat.com>

Acked-by: James Morris <jmorris@...ei.org>


> ---
> 
>  kernel/fork.c |    1 +
>  1 files changed, 1 insertions(+), 0 deletions(-)
> 
> 
> diff --git a/kernel/fork.c b/kernel/fork.c
> index bf0cef8..586874d 100644
> --- a/kernel/fork.c
> +++ b/kernel/fork.c
> @@ -1007,6 +1007,7 @@ static struct task_struct *copy_process(unsigned long clone_flags,
>  	 * triggers too late. This doesn't hurt, the check is only there
>  	 * to stop root fork bombs.
>  	 */
> +	retval = -EAGAIN;
>  	if (nr_threads >= max_threads)
>  		goto bad_fork_cleanup_count;
>  
> 

-- 
James Morris
<jmorris@...ei.org>
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