netdev - Re: [PATCH net 2/2] net: dev_queue_xmit_nit: fix potential NULL ptr dereference

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Message-ID: <1357672943.18156.328.camel@edumazet-glaptop>
Date:	Tue, 08 Jan 2013 11:22:23 -0800
From:	Eric Dumazet <eric.dumazet@...il.com>
To:	Daniel Borkmann <dborkman@...hat.com>
Cc:	David Miller <davem@...emloft.net>, netdev@...r.kernel.org,
	Changli Gao <xiaosuo@...il.com>
Subject: Re: [PATCH net 2/2] net: dev_queue_xmit_nit: fix potential NULL
 ptr dereference

On Tue, 2013-01-08 at 19:51 +0100, Daniel Borkmann wrote:
> Commit 71d9dec24dce548bf699815c976cf063ad9257e2 (``net: increase
> skb->users instead of skb_clone()'') introduced a skb_clone in
> dev_queue_xmit_nit that, when NULL, leaves the loop, but can still
> be injected into pt_prev->func().
> 
> Cc: Changli Gao <xiaosuo@...il.com>
> Cc: Eric Dumazet <eric.dumazet@...il.com>
> Signed-off-by: Daniel Borkmann <dborkman@...hat.com>
> ---
>  net/core/dev.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/net/core/dev.c b/net/core/dev.c
> index 723dcd0..6c35c33 100644
> --- a/net/core/dev.c
> +++ b/net/core/dev.c
> @@ -1827,7 +1827,7 @@ static void dev_queue_xmit_nit(struct sk_buff *skb, struct net_device *dev)
>  			pt_prev = ptype;
>  		}
>  	}
> -	if (pt_prev)
> +	if (skb2 && pt_prev)
>  		pt_prev->func(skb2, skb->dev, pt_prev, skb->dev);
>  	rcu_read_unlock();
>  }

My opinion is this patch is not needed.

pt_prev can be set only if skb2 is not NULL



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