1 files changed, 12 insertions, 8 deletions

diff --git a/drivers/net/pptp.c b/drivers/net/pptp.c
index 9c0403d0107c..89f829f5f725 100644
--- a/drivers/net/pptp.c
+++ b/drivers/net/pptp.c
@@ -307,11 +307,18 @@ static int pptp_rcv_core(struct sock *sk, struct sk_buff *skb)
 	}
 
 	header = (struct pptp_gre_header *)(skb->data);
+	headersize  = sizeof(*header);
 
 	/* test if acknowledgement present */
 	if (PPTP_GRE_IS_A(header->ver)) {
-		__u32 ack = (PPTP_GRE_IS_S(header->flags)) ?
-				header->ack : header->seq; /* ack in different place if S = 0 */
+		__u32 ack;
+
+		if (!pskb_may_pull(skb, headersize))
+			goto drop;
+		header = (struct pptp_gre_header *)(skb->data);
+
+		/* ack in different place if S = 0 */
+		ack = PPTP_GRE_IS_S(header->flags) ? header->ack : header->seq;
 
 		ack = ntohl(ack);
 
@@ -320,21 +327,18 @@ static int pptp_rcv_core(struct sock *sk, struct sk_buff *skb)
 		/* also handle sequence number wrap-around  */
 		if (WRAPPED(ack, opt->ack_recv))
 			opt->ack_recv = ack;
+	} else {
+		headersize -= sizeof(header->ack);
 	}
-
 	/* test if payload present */
 	if (!PPTP_GRE_IS_S(header->flags))
 		goto drop;
 
-	headersize  = sizeof(*header);
 	payload_len = ntohs(header->payload_len);
 	seq         = ntohl(header->seq);
 
-	/* no ack present? */
-	if (!PPTP_GRE_IS_A(header->ver))
-		headersize -= sizeof(header->ack);
 	/* check for incomplete packet (length smaller than expected) */
-	if (skb->len - headersize < payload_len)
+	if (!pskb_may_pull(skb, headersize + payload_len))
 		goto drop;
 
 	payload = skb->data + headersize;