Merge branch 'ipv4-Prevent-user-triggerable-warning'

Ido Schimmel says:

====================
net: ipv4: Prevent user triggerable warning

Patch #1 prevents a user triaggerable warning in the flow dissector by
setting 'skb->dev' in skbs used for IPv4 output route get requests.

Patch #2 adds a test case that triggers the warning without the first
patch.

I have audited all the RTM_GETROUTE handlers and could not find any
other callpath where an skb is passed to the flow dissector with both
'skb->dev' and 'skb->sk' cleared.
====================

Signed-off-by: David S. Miller <[email protected]>

Author: davem330

net/ipv4/route.c

@@ -2849,6 +2849,7 @@ static int inet_rtm_getroute(struct sk_buff *in_skb, struct nlmsghdr *nlh,
 			err = -rt->dst.error;
 	} else {
 		fl4.flowi4_iif = LOOPBACK_IFINDEX;
+		skb->dev = net->loopback_dev;
 		rt = ip_route_output_key_hash_rcu(net, &fl4, &res, skb);
 		err = 0;
 		if (IS_ERR(rt))

tools/testing/selftests/net/rtnetlink.sh

@@ -205,6 +205,8 @@ kci_test_polrouting()
 
 kci_test_route_get()
 {
+	local hash_policy=$(sysctl -n net.ipv4.fib_multipath_hash_policy)
+
 	ret=0
 
 	ip route get 127.0.0.1 > /dev/null
@@ -223,6 +225,19 @@ kci_test_route_get()
 	check_err $?
 	ip route get 10.23.7.11 from 10.23.7.12 iif "$devdummy" > /dev/null
 	check_err $?
+	ip route add 10.23.8.0/24 \
+		nexthop via 10.23.7.13 dev "$devdummy" \
+		nexthop via 10.23.7.14 dev "$devdummy"
+	check_err $?
+	sysctl -wq net.ipv4.fib_multipath_hash_policy=0
+	ip route get 10.23.8.11 > /dev/null
+	check_err $?
+	sysctl -wq net.ipv4.fib_multipath_hash_policy=1
+	ip route get 10.23.8.11 > /dev/null
+	check_err $?
+	sysctl -wq net.ipv4.fib_multipath_hash_policy="$hash_policy"
+	ip route del 10.23.8.0/24
+	check_err $?
 	ip addr del dev "$devdummy" 10.23.7.11/24
 	check_err $?