ipv4: l2tp: fix a potential issue in l2tp_ip_recv

commit 5745b8232e942abd5e16e85fa9b27cc21324acf0 upstream.

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>
Signed-off-by: Willy Tarreau <w@1wt.eu>

diff --git a/net/l2tp/l2tp_ip.c b/net/l2tp/l2tp_ip.c
index 31317f0d6a5a780f209ebc556c59f669f98928c6..81f317f841b4a8d73e149aa72ba7bf472a393c69 100644 (file)
--- a/net/l2tp/l2tp_ip.c
+++ b/net/l2tp/l2tp_ip.c
@@ -123,12 +123,11 @@ static int l2tp_ip_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;
 
@@ -156,6 +155,9 @@ 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;
                pr_debug("%s: ip recv\n", tunnel->name);
                print_hex_dump_bytes("", DUMP_PREFIX_OFFSET, ptr, length);
        }