[PATCH net v2] ipv4/route: fail early when inet dev is missing

[Paolo Abeni <pabeni@redhat.com>]

If a non local multicast packet reaches ip_route_input_rcu() while
the ingress device IPv4 private data (in_dev) is NULL, we end up
doing a NULL pointer dereference in IN_DEV_MFORWARD().

Since the later call to ip_route_input_mc() is going to fail if
!in_dev, we can fail early in such scenario and avoid the dangerous
code path.

v1 -> v2:
 - clarified the commit message, no code changes

Reported-by: Tianhao Zhao <tizhao@redhat.com>
Fixes: e58e41596811 ("net: Enable support for VRF with ipv4 multicast")
Signed-off-by: Paolo Abeni <pabeni@redhat.com>
Reviewed-by: David Ahern <dsahern@gmail.com>
---
 net/ipv4/route.c | 9 +++++----
 1 file changed, 5 insertions(+), 4 deletions(-)

diff --git a/net/ipv4/route.c b/net/ipv4/route.c
index 7bb9128c8363..e40e56e014a0 100644
--- a/net/ipv4/route.c
+++ b/net/ipv4/route.c
@@ -2144,12 +2144,13 @@ int ip_route_input_rcu(struct sk_buff *skb, __be32 daddr, __be32 saddr,
 		int our = 0;
 		int err = -EINVAL;
 
-		if (in_dev)
-			our = ip_check_mc_rcu(in_dev, daddr, saddr,
-					      ip_hdr(skb)->protocol);
+		if (!in_dev)
+			return err;
+		our = ip_check_mc_rcu(in_dev, daddr, saddr,
+				      ip_hdr(skb)->protocol);
 
 		/* check l3 master if no match yet */
-		if ((!in_dev || !our) && netif_is_l3_slave(dev)) {
+		if (!our && netif_is_l3_slave(dev)) {
 			struct in_device *l3_in_dev;
 
 			l3_in_dev = __in_dev_get_rcu(skb->dev);
-- 
2.20.1