[PATCH 5.0 008/115] net: fou: do not use guehdr after iptunnel_pull_offloads in gue_udp_recv

From: Greg Kroah-Hartman
Date: Wed Apr 24 2019 - 13:34:31 EST

From: Lorenzo Bianconi <lorenzo.bianconi@xxxxxxxxxx>

[ Upstream commit 988dc4a9a3b66be75b30405a5494faf0dc7cffb6 ]

gue tunnels run iptunnel_pull_offloads on received skbs. This can
determine a possible use-after-free accessing guehdr pointer since
the packet will be 'uncloned' running pskb_expand_head if it is a
cloned gso skb (e.g if the packet has been sent though a veth device)

Fixes: a09a4c8dd1ec ("tunnels: Remove encapsulation offloads on decap")
Signed-off-by: Lorenzo Bianconi <lorenzo.bianconi@xxxxxxxxxx>
Signed-off-by: David S. Miller <davem@xxxxxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
net/ipv4/fou.c | 4 +++-
1 file changed, 3 insertions(+), 1 deletion(-)

--- a/net/ipv4/fou.c
+++ b/net/ipv4/fou.c
@@ -121,6 +121,7 @@ static int gue_udp_recv(struct sock *sk,
struct guehdr *guehdr;
void *data;
u16 doffset = 0;
+ u8 proto_ctype;

if (!fou)
return 1;
@@ -212,13 +213,14 @@ static int gue_udp_recv(struct sock *sk,
if (unlikely(guehdr->control))
return gue_control_message(skb, guehdr);

+ proto_ctype = guehdr->proto_ctype;
__skb_pull(skb, sizeof(struct udphdr) + hdrlen);

if (iptunnel_pull_offloads(skb))
goto drop;

- return -guehdr->proto_ctype;
+ return -proto_ctype;