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Subject[PATCH 3.2 111/115] ipv4: l2tp: fix a potential issue in l2tp_ip_recv
3.2.80-rc1 review patch.  If anyone has any objections, please let me know.

------------------

From: Haishuang Yan <yanhaishuang@cmss.chinamobile.com>

[ 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>
---
net/l2tp/l2tp_ip.c | 8 +++++---
1 file changed, 5 insertions(+), 3 deletions(-)

--- a/net/l2tp/l2tp_ip.c
+++ b/net/l2tp/l2tp_ip.c
@@ -129,12 +129,11 @@ static int l2tp_ip_recv(struct sk_buff *
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 *
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;
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