[PATCH 3.12 35/78] ipv6: l2tp: fix a potential issue in l2tp_ip6_recv

From: Jiri Slaby
Date: Fri Apr 22 2016 - 07:19:41 EST


From: Haishuang Yan <yanhaishuang@xxxxxxxxxxxxxxxxxxxx>

3.12-stable review patch. If anyone has any objections, please let me know.

===============

[ Upstream commit be447f305494e019dfc37ea4cdf3b0e4200b4eba ]

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

Signed-off-by: Haishuang Yan <yanhaishuang@xxxxxxxxxxxxxxxxxxxx>
Signed-off-by: David S. Miller <davem@xxxxxxxxxxxxx>
Signed-off-by: Jiri Slaby <jslaby@xxxxxxx>
---
net/l2tp/l2tp_ip6.c | 8 +++++---
1 file changed, 5 insertions(+), 3 deletions(-)

diff --git a/net/l2tp/l2tp_ip6.c b/net/l2tp/l2tp_ip6.c
index 3b61ddd6e4a6..eadfb3031ed2 100644
--- a/net/l2tp/l2tp_ip6.c
+++ b/net/l2tp/l2tp_ip6.c
@@ -135,12 +135,11 @@ static int l2tp_ip6_recv(struct sk_buff *skb)
struct l2tp_tunnel *tunnel = NULL;
int length;

- /* 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;

@@ -168,6 +167,9 @@ static int l2tp_ip6_recv(struct sk_buff *skb)
if (!pskb_may_pull(skb, length))
goto discard;

+ /* Point to L2TP header */
+ optr = ptr = skb->data;
+ ptr += 4;
pr_debug("%s: ip recv\n", tunnel->name);
print_hex_dump_bytes("", DUMP_PREFIX_OFFSET, ptr, length);
}
--
2.8.1