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

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Message-Id: <20100316.142937.144445591.davem@davemloft.net>
Date:	Tue, 16 Mar 2010 14:29:37 -0700 (PDT)
From:	David Miller <davem@...emloft.net>
To:	mpm@...enic.com
Cc:	jirislaby@...il.com, jslaby@...e.cz, netdev@...r.kernel.org,
	linux-kernel@...r.kernel.org, danborkmann@...glemail.com
Subject: Re: [PATCH 1/1] NET: netpoll, fix potential NULL ptr dereference

From: Matt Mackall <mpm@...enic.com>
Date: Tue, 16 Mar 2010 12:56:00 -0500

> On Tue, 2010-03-16 at 18:22 +0100, Jiri Slaby wrote:
>> 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);
>>          }
> 
> Ok, you're correct, I read the second test backwards.
> 
> Acked-by: Matt Mackall <mpm@...enic.com>

Applied, thanks everyone.
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