linux-kernel - [PATCH] net: fix neigh_resolve_output can cause skb_under

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Message-ID: <CA3E5132752D1F49871ED0FC40D56BBA43ECE2E72D@EUSAACMS0701.eamcs.ericsson.se>
Date:	Fri, 28 Sep 2012 19:40:39 -0400
From:	Ramesh Nagappa <ramesh.nagappa@...csson.com>
To:	"netdev@...r.kernel.org" <netdev@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
CC:	"davem@...emloft.net" <davem@...emloft.net>,
	"gregkh@...uxfoundation.org" <gregkh@...uxfoundation.org>,
	"michel@...irati.com.br" <michel@...irati.com.br>,
	"eric.dumazet@...il.com" <eric.dumazet@...il.com>
Subject: [PATCH] net: fix neigh_resolve_output can cause skb_under_panic

>From fd023edd911ef12aca38a72b40241661c202684f Mon Sep 17 00:00:00 2001
From: Ramesh Nagappa <ramesh.nagappa@...csson.com>
Date: Thu, 27 Sep 2012 10:20:58 -0700
Subject: [PATCH] net: fix neigh_resolve_output can cause skb_under_panic

The retry loop in the neigh_resolve_output() and neigh_connected_output() can add
a hard_header without resetting the skb to network header. This causes the
skb_push() in dev_hard_header() to fail.
Signed-off-by: Ramesh Nagappa <ramesh.nagappa@...csson.com>
Signed-off-by: Shawn Lu <shawn.lu@...csson.com>
Reviewed-by: Billie Alsup <billie.alsup@...csson.com>
Reviewed-by: Robert Coulson <robert.coulson@...csson.com>
---
 net/core/neighbour.c |    3 ++-
 1 files changed, 2 insertions(+), 1 deletions(-)

diff --git a/net/core/neighbour.c b/net/core/neighbour.c
index 96bb0a3..5a3dfec5 100644
--- a/net/core/neighbour.c
+++ b/net/core/neighbour.c
@@ -1327,6 +1327,7 @@ int neigh_resolve_output(struct sk_buff *skb)
 
 		do {
 			seq = read_seqbegin(&neigh->ha_lock);
+			__skb_pull(skb, skb_network_offset(skb));
 			err = dev_hard_header(skb, dev, ntohs(skb->protocol),
 					      neigh->ha, NULL, skb->len);
 		} while (read_seqretry(&neigh->ha_lock, seq));
@@ -1358,10 +1359,10 @@ int neigh_connected_output(struct sk_buff *skb)
 	struct net_device *dev = neigh->dev;
 	unsigned int seq;
 
-	__skb_pull(skb, skb_network_offset(skb));
 
 	do {
 		seq = read_seqbegin(&neigh->ha_lock);
+		__skb_pull(skb, skb_network_offset(skb));
 		err = dev_hard_header(skb, dev, ntohs(skb->protocol),
 				      neigh->ha, NULL, skb->len);
 	} while (read_seqretry(&neigh->ha_lock, seq));
-- 
1.7.3.1
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