gtp: reload GTPv1 header after pskb_may_pull()

The GTPv1 header flags indicate the presence of optional extensions
after this header. Refresh the pointer to the GTPv1 header as skb->head
might have be reallocated via pskb_may_pull().

Fixes: 459aa660eb1d ("gtp: add initial driver for datapath of GPRS Tunneling Protocol (GTP-U)")
Reported-by: Eric Dumazet <eric.dumazet@gmail.com>
Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>
Signed-off-by: David S. Miller <davem@davemloft.net>

1 files changed, 2 insertions, 0 deletions

diff --git a/drivers/net/gtp.c b/drivers/net/gtp.c
index 8ce1104e4fdb..f7caf1e35d83 100644
--- a/drivers/net/gtp.c
+++ b/drivers/net/gtp.c
@@ -253,6 +253,8 @@ static int gtp1u_udp_encap_recv(struct gtp_dev *gtp, struct sk_buff *skb,
         if (!pskb_may_pull(skb, hdrlen))
                 return -1;
 
+        gtp1 = (struct gtp1_header *)(skb->data + sizeof(struct udphdr));
+
         rcu_read_lock();
         pctx = gtp1_pdp_find(gtp, ntohl(gtp1->tid));
         if (!pctx) {