[PATCH net-next v1] l2tp: fix reading optional fields

[Jacob Wen <jian.w.wen@oracle.com>]

Use pskb_may_pull() to make sure the optional fields are in skb linear
parts.

Signed-off-by: Jacob Wen <jian.w.wen@oracle.com>
---
v1: fix warning: ISO C90 forbids mixed declarations and code
---
 net/l2tp/l2tp_core.c | 12 +++++++++++-
 1 file changed, 11 insertions(+), 1 deletion(-)

diff --git a/net/l2tp/l2tp_core.c b/net/l2tp/l2tp_core.c
index 26f1d435696a..c0dfa2bcd218 100644
--- a/net/l2tp/l2tp_core.c
+++ b/net/l2tp/l2tp_core.c
@@ -627,6 +627,8 @@ void l2tp_recv_common(struct l2tp_session *session, struct sk_buff *skb,
 
 	/* Parse and check optional cookie */
 	if (session->peer_cookie_len > 0) {
+		if (!pskb_may_pull(skb, ptr - optr + session->peer_cookie_len))
+			goto discard;
 		if (memcmp(ptr, &session->peer_cookie[0], session->peer_cookie_len)) {
 			l2tp_info(tunnel, L2TP_MSG_DATA,
 				  "%s: cookie mismatch (%u/%u). Discarding.\n",
@@ -649,6 +651,8 @@ void l2tp_recv_common(struct l2tp_session *session, struct sk_buff *skb,
 	L2TP_SKB_CB(skb)->has_seq = 0;
 	if (tunnel->version == L2TP_HDR_VER_2) {
 		if (hdrflags & L2TP_HDRFLAG_S) {
+			if (!pskb_may_pull(skb, ptr - optr + 4))
+				goto discard;
 			ns = ntohs(*(__be16 *) ptr);
 			ptr += 2;
 			nr = ntohs(*(__be16 *) ptr);
@@ -663,8 +667,12 @@ void l2tp_recv_common(struct l2tp_session *session, struct sk_buff *skb,
 				 session->name, ns, nr, session->nr);
 		}
 	} else if (session->l2specific_type == L2TP_L2SPECTYPE_DEFAULT) {
-		u32 l2h = ntohl(*(__be32 *) ptr);
+		u32 l2h;
+
+		if (!pskb_may_pull(skb, ptr - optr + 4))
+			goto discard;
 
+		l2h = ntohl(*(__be32 *) ptr);
 		if (l2h & 0x40000000) {
 			ns = l2h & 0x00ffffff;
 
@@ -729,6 +737,8 @@ void l2tp_recv_common(struct l2tp_session *session, struct sk_buff *skb,
 	if (tunnel->version == L2TP_HDR_VER_2) {
 		/* If offset bit set, skip it. */
 		if (hdrflags & L2TP_HDRFLAG_O) {
+			if (!pskb_may_pull(skb, ptr - optr + 2))
+				goto discard;
 			offset = ntohs(*(__be16 *)ptr);
 			ptr += 2 + offset;
 		}
-- 
2.17.1