[PATCH AUTOSEL for 4.14 077/100] xfrm: Fix stack-out-of-bounds read on socket policy lookup.

[Sasha Levin]

From: Steffen Klassert <steffen.klassert@xxxxxxxxxxx>

[ Upstream commit ddc47e4404b58f03e98345398fb12d38fe291512 ]

When we do tunnel or beet mode, we pass saddr and daddr from the
template to xfrm_state_find(), this is ok. On transport mode,
we pass the addresses from the flowi, assuming that the IP
addresses (and address family) don't change during transformation.
This assumption is wrong in the IPv4 mapped IPv6 case, packet
is IPv4 and template is IPv6.

Fix this by catching address family missmatches of the policy
and the flow already before we do the lookup.

Reported-by: syzbot <syzkaller@xxxxxxxxxxxxxxxx>
Signed-off-by: Steffen Klassert <steffen.klassert@xxxxxxxxxxx>
Signed-off-by: Sasha Levin <alexander.levin@xxxxxxxxxxxxx>
---
 net/xfrm/xfrm_policy.c | 8 +++++++-
 1 file changed, 7 insertions(+), 1 deletion(-)

diff --git a/net/xfrm/xfrm_policy.c b/net/xfrm/xfrm_policy.c
index 6bc16bb61b55..50c5f46b5cca 100644
--- a/net/xfrm/xfrm_policy.c
+++ b/net/xfrm/xfrm_policy.c
@@ -1169,9 +1169,15 @@ static struct xfrm_policy *xfrm_sk_policy_lookup(const struct sock *sk, int dir,
  again:
 	pol = rcu_dereference(sk->sk_policy[dir]);
 	if (pol != NULL) {
-		bool match = xfrm_selector_match(&pol->selector, fl, family);
+		bool match;
 		int err = 0;
 
+		if (pol->family != family) {
+			pol = NULL;
+			goto out;
+		}
+
+		match = xfrm_selector_match(&pol->selector, fl, family);
 		if (match) {
 			if ((sk->sk_mark & pol->mark.m) != pol->mark.v) {
 				pol = NULL;
-- 
2.11.0