netdev - [BUG] eth_type_trans() can access stale data

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Message-ID: <1389743541.31367.279.camel@edumazet-glaptop2.roam.corp.google.com>
Date:	Tue, 14 Jan 2014 15:52:21 -0800
From:	Eric Dumazet <eric.dumazet@...il.com>
To:	David Miller <davem@...emloft.net>
Cc:	netdev <netdev@...r.kernel.org>
Subject: [BUG] eth_type_trans() can access stale data

Following code :

if (unlikely(skb->len >= 2 && *(unsigned short *)(skb->data) == 0xFFFF))
	return htons(ETH_P_802_3);

expects the additional bytes are in skb->head

I do not think all eth_type_trans() are ready for a pskb_may_pull()
(I am too lazy to perform a whole check)

Would following workaround be OK ?

diff --git a/net/ethernet/eth.c b/net/ethernet/eth.c
index 8f032bae60ad..d95403098f09 100644
--- a/net/ethernet/eth.c
+++ b/net/ethernet/eth.c
@@ -194,7 +194,8 @@ __be16 eth_type_trans(struct sk_buff *skb, struct net_device *dev)
 	 *      layer. We look for FFFF which isn't a used 802.2 SSAP/DSAP. This
 	 *      won't work for fault tolerant netware but does for the rest.
 	 */
-	if (unlikely(skb->len >= 2 && *(unsigned short *)(skb->data) == 0xFFFF))
+	if (unlikely(skb_headlen(skb) >= 2 &&
+		     *(unsigned short *)(skb->data) == 0xFFFF))
 		return htons(ETH_P_802_3);
 
 	/*



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