linux-kernel - Re: [PATCH] gfs2: fix potential NULL pointer dereference

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Date:	Tue, 12 Nov 2013 12:35:12 +0000
From:	Steven Whitehouse <swhiteho@...hat.com>
To:	Michal Nazarewicz <mpn@...gle.com>
Cc:	cluster-devel@...hat.com, linux-kernel@...r.kernel.org,
	Michal Nazarewicz <mina86@...a86.com>
Subject: Re: [PATCH] gfs2: fix potential NULL pointer dereference

Hi,

Yes, good catch. Thanks, I'll add it to the tree,

Steve.

On Tue, 2013-11-12 at 13:30 +0100, Michal Nazarewicz wrote:
> From: Michal Nazarewicz <mina86@...a86.com>
> 
> Commit [e66cf1610: GFS2: Use lockref for glocks] replaced call:
>     atomic_read(&gi->gl->gl_ref) == 0
> with:
>     __lockref_is_dead(&gl->gl_lockref)
> therefore changing how gl is accessed, from gi->gl to plan gl.
> However, gl can be a NULL pointer, and so gi->gl needs to be
> used instead (which is guaranteed not to be NULL because fo
> the while loop checking that condition).
> 
> Signed-off-by: Michal Nazarewicz <mina86@...a86.com>
> ---
>  fs/gfs2/glock.c | 3 ++-
>  1 file changed, 2 insertions(+), 1 deletion(-)
> 
> diff --git a/fs/gfs2/glock.c b/fs/gfs2/glock.c
> index e66a800..c8420f7 100644
> --- a/fs/gfs2/glock.c
> +++ b/fs/gfs2/glock.c
> @@ -1899,7 +1899,8 @@ static int gfs2_glock_iter_next(struct gfs2_glock_iter *gi)
>  			gi->nhash = 0;
>  		}
>  	/* Skip entries for other sb and dead entries */
> -	} while (gi->sdp != gi->gl->gl_sbd || __lockref_is_dead(&gl->gl_lockref));
> +	} while (gi->sdp != gi->gl->gl_sbd ||
> +		 __lockref_is_dead(&gi->gl->gl_lockref));
>  
>  	return 0;
>  }


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