From: Haishuang Yan <yanhaishuang@cmss.chinamobile.com>
Date: Sun, 3 Apr 2016 14:09:23 +0000 (+0800)
Subject: ipv4: l2tp: fix a potential issue in l2tp_ip_recv
X-Git-Tag: v3.2.80~5
X-Git-Url: http://git.openpandora.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=f56bbe05031ec62fed752671fdf510cc202b67cf;p=pandora-kernel.git

ipv4: l2tp: fix a potential issue in l2tp_ip_recv

[ Upstream commit 5745b8232e942abd5e16e85fa9b27cc21324acf0 ]

pskb_may_pull() can change skb->data, so we have to load ptr/optr at the
right place.

Signed-off-by: Haishuang Yan <yanhaishuang@cmss.chinamobile.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
[bwh: Backported to 3.2: adjust context]
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>
---

diff --git a/net/l2tp/l2tp_ip.c b/net/l2tp/l2tp_ip.c
index 334a93d1a8ed..2d9b98ecbd73 100644
--- a/net/l2tp/l2tp_ip.c
+++ b/net/l2tp/l2tp_ip.c
@@ -129,12 +129,11 @@ static int l2tp_ip_recv(struct sk_buff *skb)
 	int length;
 	int offset;
 
-	/* Point to L2TP header */
-	optr = ptr = skb->data;
-
 	if (!pskb_may_pull(skb, 4))
 		goto discard;
 
+	/* Point to L2TP header */
+	optr = ptr = skb->data;
 	session_id = ntohl(*((__be32 *) ptr));
 	ptr += 4;
 
@@ -162,6 +161,9 @@ static int l2tp_ip_recv(struct sk_buff *skb)
 		if (!pskb_may_pull(skb, length))
 			goto discard;
 
+		/* Point to L2TP header */
+		optr = ptr = skb->data;
+		ptr += 4;
 		printk(KERN_DEBUG "%s: ip recv: ", tunnel->name);
 
 		offset = 0;