flow_dissector: fix TTL and TOS dissection on IPv4 fragments

the following command:

 # tc filter add dev $h2 ingress protocol ip pref 1 handle 101 flower \
   $tcflags dst_ip 192.0.2.2 ip_ttl 63 action drop

doesn't drop all IPv4 packets that match the configured TTL / destination
address. In particular, if "fragment offset" or "more fragments" have non
zero value in the IPv4 header, setting of FLOW_DISSECTOR_KEY_IP is simply
ignored. Fix this dissecting IPv4 TTL and TOS before fragment info; while
at it, add a selftest for tc flower's match on 'ip_ttl' that verifies the
correct behavior.

Fixes: 518d8a2e ("net/flow_dissector: add support for dissection of misc ip header fields")
Reported-by: Shuang Li <shuali@redhat.com>
Signed-off-by: Davide Caratti <dcaratti@redhat.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

net/core/flow_dissector.c

@@ -1050,6 +1050,9 @@ bool __skb_flow_dissect(const struct net *net,
 			key_control->addr_type = FLOW_DISSECTOR_KEY_IPV4_ADDRS;
 		}
 
+		__skb_flow_dissect_ipv4(skb, flow_dissector,
+					target_container, data, iph);
+
 		if (ip_is_fragment(iph)) {
 			key_control->flags |= FLOW_DIS_IS_FRAGMENT;
 
@@ -1066,9 +1069,6 @@ bool __skb_flow_dissect(const struct net *net,
 			}
 		}
 
-		__skb_flow_dissect_ipv4(skb, flow_dissector,
-					target_container, data, iph);
-
 		break;
 	}
 	case htons(ETH_P_IPV6): {

tools/testing/selftests/net/forwarding/tc_flower.sh

@@ -3,7 +3,7 @@
 
 ALL_TESTS="match_dst_mac_test match_src_mac_test match_dst_ip_test \
 	match_src_ip_test match_ip_flags_test match_pcp_test match_vlan_test \
-	match_ip_tos_test match_indev_test"
+	match_ip_tos_test match_indev_test match_ip_ttl_test"
 NUM_NETIFS=2
 source tc_common.sh
 source lib.sh
@@ -310,6 +310,42 @@ match_ip_tos_test()
 	log_test "ip_tos match ($tcflags)"
 }
 
+match_ip_ttl_test()
+{
+	RET=0
+
+	tc filter add dev $h2 ingress protocol ip pref 1 handle 101 flower \
+		$tcflags dst_ip 192.0.2.2 ip_ttl 63 action drop
+	tc filter add dev $h2 ingress protocol ip pref 2 handle 102 flower \
+		$tcflags dst_ip 192.0.2.2 action drop
+
+	$MZ $h1 -c 1 -p 64 -a $h1mac -b $h2mac -A 192.0.2.1 -B 192.0.2.2 \
+		-t ip "ttl=63" -q
+
+	$MZ $h1 -c 1 -p 64 -a $h1mac -b $h2mac -A 192.0.2.1 -B 192.0.2.2 \
+		-t ip "ttl=63,mf,frag=256" -q
+
+	tc_check_packets "dev $h2 ingress" 102 1
+	check_fail $? "Matched on the wrong filter (no check on ttl)"
+
+	tc_check_packets "dev $h2 ingress" 101 2
+	check_err $? "Did not match on correct filter (ttl=63)"
+
+	$MZ $h1 -c 1 -p 64 -a $h1mac -b $h2mac -A 192.0.2.1 -B 192.0.2.2 \
+		-t ip "ttl=255" -q
+
+	tc_check_packets "dev $h2 ingress" 101 3
+	check_fail $? "Matched on a wrong filter (ttl=63)"
+
+	tc_check_packets "dev $h2 ingress" 102 1
+	check_err $? "Did not match on correct filter (no check on ttl)"
+
+	tc filter del dev $h2 ingress protocol ip pref 2 handle 102 flower
+	tc filter del dev $h2 ingress protocol ip pref 1 handle 101 flower
+
+	log_test "ip_ttl match ($tcflags)"
+}
+
 match_indev_test()
 {
 	RET=0