Merge branch 'ipv4-handle-tos-and-scope-properly-for-icmp-redirects-and-pmtu-updates'

Guillaume Nault says:

====================
ipv4: Handle TOS and scope properly for ICMP redirects and PMTU updates

ICMPv4 PMTU and redirect handlers didn't properly initialise the
struct flowi4 they used for route lookups:

* ECN bits sometimes weren't cleared from ->flowi4_tos.
* The RTO_ONLINK flag wasn't taken into account for ->flowi4_scope.

In some special cases, this resulted in ICMP redirects and PMTU updates
not being taken into account because fib_lookup() couldn't retrieve the
correct route.
====================

Link: https://lore.kernel.org/r/[e-mail]
Signed-off-by: Jakub Kicinski <[e-mail]>

net/ipv4/route.c

···
 }
 EXPORT_SYMBOL(__ip_select_ident);
 
+static void ip_rt_fix_tos(struct flowi4 *fl4)
+{
+	__u8 tos = RT_FL_TOS(fl4);
+
+	fl4->flowi4_tos = tos & IPTOS_RT_MASK;
+	fl4->flowi4_scope = tos & RTO_ONLINK ?
+			    RT_SCOPE_LINK : RT_SCOPE_UNIVERSE;
+}
+
 static void __build_flow_key(const struct net *net, struct flowi4 *fl4,
 			     const struct sock *sk,
 			     const struct iphdr *iph,
···
 	rt = (struct rtable *) dst;
 
 	__build_flow_key(net, &fl4, sk, iph, oif, tos, prot, mark, 0);
+	ip_rt_fix_tos(&fl4);
 	__ip_do_redirect(rt, skb, &fl4, true);
 }
 
···
 	struct flowi4 fl4;
 
 	ip_rt_build_flow_key(&fl4, sk, skb);
+	ip_rt_fix_tos(&fl4);
 
 	/* Don't make lookup fail for bridged encapsulations */
 	if (skb && netif_is_any_bridge_port(skb->dev))
···
 			goto out;
 
 		new = true;
+	} else {
+		ip_rt_fix_tos(&fl4);
 	}
 
 	__ip_rt_update_pmtu((struct rtable *)xfrm_dst_path(&rt->dst), &fl4, mtu);
···
 struct rtable *ip_route_output_key_hash(struct net *net, struct flowi4 *fl4,
 					const struct sk_buff *skb)
 {
-	__u8 tos = RT_FL_TOS(fl4);
 	struct fib_result res = {
 		.type		= RTN_UNSPEC,
 		.fi		= NULL,
···
 	struct rtable *rth;
 
 	fl4->flowi4_iif = LOOPBACK_IFINDEX;
-	fl4->flowi4_tos = tos & IPTOS_RT_MASK;
-	fl4->flowi4_scope = ((tos & RTO_ONLINK) ?
-			 RT_SCOPE_LINK : RT_SCOPE_UNIVERSE);
+	ip_rt_fix_tos(fl4);
 
 	rcu_read_lock();
 	rth = ip_route_output_key_hash_rcu(net, fl4, &res, skb);

tools/testing/selftests/net/pmtu.sh

···
 # - pmtu_ipv6
 #	Same as pmtu_ipv4, except for locked PMTU tests, using IPv6
 #
+# - pmtu_ipv4_dscp_icmp_exception
+#	Set up the same network topology as pmtu_ipv4, but use non-default
+#	routing table in A. A fib-rule is used to jump to this routing table
+#	based on DSCP. Send ICMPv4 packets with the expected DSCP value and
+#	verify that ECN doesn't interfere with the creation of PMTU exceptions.
+#
+# - pmtu_ipv4_dscp_udp_exception
+#	Same as pmtu_ipv4_dscp_icmp_exception, but use UDP instead of ICMP.
+#
 # - pmtu_ipv4_vxlan4_exception
 #	Set up the same network topology as pmtu_ipv4, create a VXLAN tunnel
 #	over IPv4 between A and B, routed via R1. On the link between R1 and B,
···
 tests="
 	pmtu_ipv4_exception		ipv4: PMTU exceptions			1
 	pmtu_ipv6_exception		ipv6: PMTU exceptions			1
+	pmtu_ipv4_dscp_icmp_exception	ICMPv4 with DSCP and ECN: PMTU exceptions	1
+	pmtu_ipv4_dscp_udp_exception	UDPv4 with DSCP and ECN: PMTU exceptions	1
 	pmtu_ipv4_vxlan4_exception	IPv4 over vxlan4: PMTU exceptions	1
 	pmtu_ipv6_vxlan4_exception	IPv6 over vxlan4: PMTU exceptions	1
 	pmtu_ipv4_vxlan6_exception	IPv4 over vxlan6: PMTU exceptions	1
···
 	B	6	default			61
 "
 
+policy_mark=0x04
+rt_table=main
+
 veth4_a_addr="192.168.1.1"
 veth4_b_addr="192.168.1.2"
 veth4_c_addr="192.168.2.10"
···
 err_buf=
 tcpdump_pids=
 nettest_pids=
+socat_pids=
 
 err() {
 	err_buf="${err_buf}${1}
···
 
 		ns_name="$(nsname ${ns})"
 
-		ip -n ${ns_name} route add ${addr} via ${gw}
+		ip -n "${ns_name}" route add "${addr}" table "${rt_table}" via "${gw}"
 
 		ns=""; addr=""; gw=""
 	done
···
 
 		ns_name="$(nsname ${ns})"
 
-		ip -n ${ns_name} -${fam} route add ${addr} nhid ${nhid}
+		ip -n "${ns_name}" -"${fam}" route add "${addr}" table "${rt_table}" nhid "${nhid}"
 
 		ns=""; fam=""; addr=""; nhid=""
 	done
···
 	fi
 
 	return 0
+}
+
+setup_policy_routing() {
+	setup_routing
+
+	ip -netns "${NS_A}" -4 rule add dsfield "${policy_mark}" \
+		table "${rt_table}"
+
+	# Set the IPv4 Don't Fragment bit with tc, since socat doesn't seem to
+	# have an option do to it.
+	tc -netns "${NS_A}" qdisc replace dev veth_A-R1 root prio
+	tc -netns "${NS_A}" qdisc replace dev veth_A-R2 root prio
+	tc -netns "${NS_A}" filter add dev veth_A-R1                      \
+		protocol ipv4 flower ip_proto udp                         \
+		action pedit ex munge ip df set 0x40 pipe csum ip and udp
+	tc -netns "${NS_A}" filter add dev veth_A-R2                      \
+		protocol ipv4 flower ip_proto udp                         \
+		action pedit ex munge ip df set 0x40 pipe csum ip and udp
 }
 
 setup_bridge() {
···
 	done
 	nettest_pids=
 
+	for pid in ${socat_pids}; do
+		kill "${pid}"
+	done
+	socat_pids=
+
 	for n in ${NS_A} ${NS_B} ${NS_C} ${NS_R1} ${NS_R2}; do
 		ip netns del ${n} 2> /dev/null
 	done
···
 route_get_dst_exception() {
 	ns_cmd="${1}"
 	dst="${2}"
+	dsfield="${3}"
 
-	${ns_cmd} ip route get "${dst}"
+	if [ -z "${dsfield}" ]; then
+		dsfield=0
+	fi
+
+	${ns_cmd} ip route get "${dst}" dsfield "${dsfield}"
 }
 
 route_get_dst_pmtu_from_exception() {
 	ns_cmd="${1}"
 	dst="${2}"
+	dsfield="${3}"
 
-	mtu_parse "$(route_get_dst_exception "${ns_cmd}" ${dst})"
+	mtu_parse "$(route_get_dst_exception "${ns_cmd}" "${dst}" "${dsfield}")"
 }
 
 check_pmtu_value() {
···
 
 test_pmtu_ipv6_exception() {
 	test_pmtu_ipvX 6
+}
+
+test_pmtu_ipv4_dscp_icmp_exception() {
+	rt_table=100
+
+	setup namespaces policy_routing || return $ksft_skip
+	trace "${ns_a}"  veth_A-R1    "${ns_r1}" veth_R1-A \
+	      "${ns_r1}" veth_R1-B    "${ns_b}"  veth_B-R1 \
+	      "${ns_a}"  veth_A-R2    "${ns_r2}" veth_R2-A \
+	      "${ns_r2}" veth_R2-B    "${ns_b}"  veth_B-R2
+
+	# Set up initial MTU values
+	mtu "${ns_a}"  veth_A-R1 2000
+	mtu "${ns_r1}" veth_R1-A 2000
+	mtu "${ns_r1}" veth_R1-B 1400
+	mtu "${ns_b}"  veth_B-R1 1400
+
+	mtu "${ns_a}"  veth_A-R2 2000
+	mtu "${ns_r2}" veth_R2-A 2000
+	mtu "${ns_r2}" veth_R2-B 1500
+	mtu "${ns_b}"  veth_B-R2 1500
+
+	len=$((2000 - 20 - 8)) # Fills MTU of veth_A-R1
+
+	dst1="${prefix4}.${b_r1}.1"
+	dst2="${prefix4}.${b_r2}.1"
+
+	# Create route exceptions
+	dsfield=${policy_mark} # No ECN bit set (Not-ECT)
+	run_cmd "${ns_a}" ping -q -M want -Q "${dsfield}" -c 1 -w 1 -s "${len}" "${dst1}"
+
+	dsfield=$(printf "%#x" $((policy_mark + 0x02))) # ECN=2 (ECT(0))
+	run_cmd "${ns_a}" ping -q -M want -Q "${dsfield}" -c 1 -w 1 -s "${len}" "${dst2}"
+
+	# Check that exceptions have been created with the correct PMTU
+	pmtu_1="$(route_get_dst_pmtu_from_exception "${ns_a}" "${dst1}" "${policy_mark}")"
+	check_pmtu_value "1400" "${pmtu_1}" "exceeding MTU" || return 1
+
+	pmtu_2="$(route_get_dst_pmtu_from_exception "${ns_a}" "${dst2}" "${policy_mark}")"
+	check_pmtu_value "1500" "${pmtu_2}" "exceeding MTU" || return 1
+}
+
+test_pmtu_ipv4_dscp_udp_exception() {
+	rt_table=100
+
+	if ! which socat > /dev/null 2>&1; then
+		echo "'socat' command not found; skipping tests"
+		return $ksft_skip
+	fi
+
+	setup namespaces policy_routing || return $ksft_skip
+	trace "${ns_a}"  veth_A-R1    "${ns_r1}" veth_R1-A \
+	      "${ns_r1}" veth_R1-B    "${ns_b}"  veth_B-R1 \
+	      "${ns_a}"  veth_A-R2    "${ns_r2}" veth_R2-A \
+	      "${ns_r2}" veth_R2-B    "${ns_b}"  veth_B-R2
+
+	# Set up initial MTU values
+	mtu "${ns_a}"  veth_A-R1 2000
+	mtu "${ns_r1}" veth_R1-A 2000
+	mtu "${ns_r1}" veth_R1-B 1400
+	mtu "${ns_b}"  veth_B-R1 1400
+
+	mtu "${ns_a}"  veth_A-R2 2000
+	mtu "${ns_r2}" veth_R2-A 2000
+	mtu "${ns_r2}" veth_R2-B 1500
+	mtu "${ns_b}"  veth_B-R2 1500
+
+	len=$((2000 - 20 - 8)) # Fills MTU of veth_A-R1
+
+	dst1="${prefix4}.${b_r1}.1"
+	dst2="${prefix4}.${b_r2}.1"
+
+	# Create route exceptions
+	run_cmd_bg "${ns_b}" socat UDP-LISTEN:50000 OPEN:/dev/null,wronly=1
+	socat_pids="${socat_pids} $!"
+
+	dsfield=${policy_mark} # No ECN bit set (Not-ECT)
+	run_cmd "${ns_a}" socat OPEN:/dev/zero,rdonly=1,readbytes="${len}" \
+		UDP:"${dst1}":50000,tos="${dsfield}"
+
+	dsfield=$(printf "%#x" $((policy_mark + 0x02))) # ECN=2 (ECT(0))
+	run_cmd "${ns_a}" socat OPEN:/dev/zero,rdonly=1,readbytes="${len}" \
+		UDP:"${dst2}":50000,tos="${dsfield}"
+
+	# Check that exceptions have been created with the correct PMTU
+	pmtu_1="$(route_get_dst_pmtu_from_exception "${ns_a}" "${dst1}" "${policy_mark}")"
+	check_pmtu_value "1400" "${pmtu_1}" "exceeding MTU" || return 1
+	pmtu_2="$(route_get_dst_pmtu_from_exception "${ns_a}" "${dst2}" "${policy_mark}")"
+	check_pmtu_value "1500" "${pmtu_2}" "exceeding MTU" || return 1
 }
 
 test_pmtu_ipvX_over_vxlanY_or_geneveY_exception() {