netdev - [PATCH net] flow_dissector: fix TTL and TOS dissection on IPv4 fragments

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Message-Id: <a33c38298e722bc1d2ce4ecd13bb5f42d6859709.1613142439.git.dcaratti@redhat.com>
Date:   Fri, 12 Feb 2021 16:12:25 +0100
From:   Davide Caratti <dcaratti@...hat.com>
To:     "David S. Miller" <davem@...emloft.net>,
        Jakub Kicinski <kuba@...nel.org>,
        Or Gerlitz <ogerlitz@...lanox.com>,
        Jiri Pirko <jiri@...lanox.com>, netdev@...r.kernel.org
Cc:     shuali@...hat.com
Subject: [PATCH net] 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: 518d8a2e9bad ("net/flow_dissector: add support for dissection of misc ip header fields")
Reported-by: Shuang Li <shuali@...hat.com>
Signed-off-by: Davide Caratti <dcaratti@...hat.com>
---
 net/core/flow_dissector.c                     |  6 +--
 .../selftests/net/forwarding/tc_flower.sh     | 38 ++++++++++++++++++-
 2 files changed, 40 insertions(+), 4 deletions(-)

diff --git a/net/core/flow_dissector.c b/net/core/flow_dissector.c
index 6f1adba6695f..0b4f536bc32d 100644
--- a/net/core/flow_dissector.c
+++ b/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): {
diff --git a/tools/testing/selftests/net/forwarding/tc_flower.sh b/tools/testing/selftests/net/forwarding/tc_flower.sh
index 058c746ee300..b11d8e6b5bc1 100755
--- a/tools/testing/selftests/net/forwarding/tc_flower.sh
+++ b/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
-- 
2.29.2