linux-kernel - Re: [patch] afs: potential null dereference

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Message-ID: <20100322125626.GM21571@bicker>
Date:	Mon, 22 Mar 2010 15:56:26 +0300
From:	Dan Carpenter <error27@...il.com>
To:	David Howells <dhowells@...hat.com>
Cc:	kernel-janitors@...r.kernel.org, linux-afs@...ts.infradead.org,
	linux-kernel@...r.kernel.org
Subject: Re: [patch] afs: potential null dereference

On Mon, Mar 22, 2010 at 12:05:20PM +0000, David Howells wrote:
> Dan Carpenter <error27@...il.com> wrote:
> 
> > It seems clear from the surrounding code that xpermits is allowed to be 
> > NULL here.
> 
> Interesting.  The memcpy() won't oops due to this because if it is given a
> NULL pointer, it will also be given a zero count.  I wonder if this means the
> if-statement your patch adds is actually unnecessary...
> 

I was concerned about the dereference here:

+       if (xpermits)
+               memcpy(permits->permits, xpermits->permits,
                                         ^^^^^^^^^^^^^^^^^
+                       count * sizeof(struct afs_permit));

This code has been there for three years, so yeah, you would think if it
were a problem someone would have complained.  My theory was "xpermits"
was almost always non-null.

regards,
dan carpenter

> David
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