netdev - Re: [PATCH 1/1] NET: netpoll, fix potential NULL ptr dereference

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Date:	Tue, 16 Mar 2010 18:22:17 +0100
From:	Jiri Slaby <jirislaby@...il.com>
To:	Matt Mackall <mpm@...enic.com>
CC:	Jiri Slaby <jslaby@...e.cz>, davem@...emloft.net,
	netdev@...r.kernel.org, linux-kernel@...r.kernel.org,
	Daniel Borkmann <danborkmann@...glemail.com>
Subject: Re: [PATCH 1/1] NET: netpoll, fix potential NULL ptr dereference

On 03/16/2010 06:12 PM, Matt Mackall wrote:
> I don't get it. The source of the branch tests for !ndev->npinfo and the
> original destination of the branch also tests for !ndev->npinfo. I don't
> see how it gets dereferenced.

Let's look at more of the context:
         if (!ndev->npinfo) {
                 npinfo = kmalloc(sizeof(*npinfo), GFP_KERNEL);
                 if (!npinfo) {         // npinfo is NULL
                         err = -ENOMEM;
                         goto release;
                 }
...
release:                           // npinfo is still NULL
         if (!ndev->npinfo) {       // condition is the same (holds)
              // dereference below: vvvvvvvvvvvvvvv
                 spin_lock_irqsave(&npinfo->rx_lock, flags);
                 list_for_each_entry_safe(npe, tmp, &npinfo->rx_np, rx) {
                         npe->dev = NULL;
                 }
                 spin_unlock_irqrestore(&npinfo->rx_lock, flags);

                 kfree(npinfo);
         }

thanks,
-- 
js
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