[PATCH 5.1 17/98] vxlan: Dont assume linear buffers in error handler

[Greg Kroah-Hartman]

From: Stefano Brivio <sbrivio@xxxxxxxxxx>

[ Upstream commit 8399a6930d12f5965230f4ff058228a4cc80c0b9 ]

In commit c3a43b9fec8a ("vxlan: ICMP error lookup handler") I wrongly
assumed buffers from icmp_socket_deliver() would be linear. This is not
the case: icmp_socket_deliver() only guarantees we have 8 bytes of linear
data.

Eric fixed this same issue for fou and fou6 in commits 26fc181e6cac
("fou, fou6: do not assume linear skbs") and 5355ed6388e2 ("fou, fou6:
avoid uninit-value in gue_err() and gue6_err()").

Use pskb_may_pull() instead of checking skb->len, and take into account
the fact we later access the VXLAN header with udp_hdr(), so we also
need to sum skb_transport_header() here.

Reported-by: Guillaume Nault <gnault@xxxxxxxxxx>
Fixes: c3a43b9fec8a ("vxlan: ICMP error lookup handler")
Signed-off-by: Stefano Brivio <sbrivio@xxxxxxxxxx>
Signed-off-by: David S. Miller <davem@xxxxxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
---
 drivers/net/vxlan.c |    2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

--- a/drivers/net/vxlan.c
+++ b/drivers/net/vxlan.c
@@ -1765,7 +1765,7 @@ static int vxlan_err_lookup(struct sock
 	struct vxlanhdr *hdr;
 	__be32 vni;
 
-	if (skb->len < VXLAN_HLEN)
+	if (!pskb_may_pull(skb, skb_transport_offset(skb) + VXLAN_HLEN))
 		return -EINVAL;
 
 	hdr = vxlan_hdr(skb);