[PATCH net v3 1/2] ip: fix dflt addr selection for connected nexthop

[PATCH net v3 1/2] ip: fix dflt addr selection for connected nexthop

[Nicolas Dichtel]

When a nexthop is added, without a gw address, the default scope was set
to 'host'. Thus, when a source address is selected, 127.0.0.1 may be chosen
but rejected when the route is used.

When using a route without a nexthop id, the scope can be configured in the
route, thus the problem doesn't exist.

To explain more deeply: when a user creates a nexthop, it cannot specify
the scope. To create it, the function nh_create_ipv4() calls fib_check_nh()
with scope set to 0. fib_check_nh() calls fib_check_nh_nongw() wich was
setting scope to 'host'. Then, nh_create_ipv4() calls
fib_info_update_nhc_saddr() with scope set to 'host'. The src addr is
chosen before the route is inserted.

When a 'standard' route (ie without a reference to a nexthop) is added,
fib_create_info() calls fib_info_update_nhc_saddr() with the scope set by
the user. iproute2 set the scope to 'link' by default.

Here is a way to reproduce the problem:
ip netns add foo
ip -n foo link set lo up
ip netns add bar
ip -n bar link set lo up
sleep 1

ip -n foo link add name eth0 type dummy
ip -n foo link set eth0 up
ip -n foo address add 192.168.0.1/24 dev eth0

ip -n foo link add name veth0 type veth peer name veth1 netns bar
ip -n foo link set veth0 up
ip -n bar link set veth1 up

ip -n bar address add 192.168.1.1/32 dev veth1
ip -n bar route add default dev veth1

ip -n foo nexthop add id 1 dev veth0
ip -n foo route add 192.168.1.1 nhid 1

Try to get/use the route:
> $ ip -n foo route get 192.168.1.1
> RTNETLINK answers: Invalid argument
> $ ip netns exec foo ping -c1 192.168.1.1
> ping: connect: Invalid argument

Try without nexthop group (iproute2 sets scope to 'link' by dflt):
ip -n foo route del 192.168.1.1
ip -n foo route add 192.168.1.1 dev veth0

Try to get/use the route:
> $ ip -n foo route get 192.168.1.1
> 192.168.1.1 dev veth0 src 192.168.0.1 uid 0
>     cache
> $ ip netns exec foo ping -c1 192.168.1.1
> PING 192.168.1.1 (192.168.1.1) 56(84) bytes of data.
> 64 bytes from 192.168.1.1: icmp_seq=1 ttl=64 time=0.039 ms
>
> --- 192.168.1.1 ping statistics ---
> 1 packets transmitted, 1 received, 0% packet loss, time 0ms
> rtt min/avg/max/mdev = 0.039/0.039/0.039/0.000 ms

CC: stable@vger.kernel.org
Fixes: 597cfe4fc339 ("nexthop: Add support for IPv4 nexthops")
Reported-by: Edwin Brossette <edwin.brossette@6wind.com>
Signed-off-by: Nicolas Dichtel <nicolas.dichtel@6wind.com>
---

v2 -> v3:
 - no change

v1 -> v2:
 - remove useless arp off / fixed mac settings in the description

 net/ipv4/fib_semantics.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/net/ipv4/fib_semantics.c b/net/ipv4/fib_semantics.c
index a57ba23571c9..20177ecf5bdd 100644
--- a/net/ipv4/fib_semantics.c
+++ b/net/ipv4/fib_semantics.c
@@ -1230,7 +1230,7 @@ static int fib_check_nh_nongw(struct net *net, struct fib_nh *nh,
 
 	nh->fib_nh_dev = in_dev->dev;
 	dev_hold_track(nh->fib_nh_dev, &nh->fib_nh_dev_tracker, GFP_ATOMIC);
-	nh->fib_nh_scope = RT_SCOPE_HOST;
+	nh->fib_nh_scope = RT_SCOPE_LINK;
 	if (!netif_carrier_ok(nh->fib_nh_dev))
 		nh->fib_nh_flags |= RTNH_F_LINKDOWN;
 	err = 0;
-- 
2.33.0

[PATCH net v3 2/2] selftests/net: test nexthop without gw

[Nicolas Dichtel]

This test implement the scenario described in the commit
"ip: fix dflt addr selection for connected nexthop".
The test configures a nexthop object with an output device only (no gateway
address) and a route that uses this nexthop. The goal is to check if the
kernel selects a valid source address.

Link: https://lore.kernel.org/netdev/20220712095545.10947-1-nicolas.dichtel@6wind.com/
Signed-off-by: Nicolas Dichtel <nicolas.dichtel@6wind.com>
---

v2 -> v3:
 - add more details in the commit log

v1 -> v2:
 - add linux-kselftest@vger.kernel.org
 - clean trailing whitespaces
 - add a 'trap' on exit
 - remove useless sleep
 - remove useless arp off / fixed mac settings

 tools/testing/selftests/net/Makefile          |   2 +-
 .../selftests/net/fib_nexthop_nongw.sh        | 119 ++++++++++++++++++
 2 files changed, 120 insertions(+), 1 deletion(-)
 create mode 100755 tools/testing/selftests/net/fib_nexthop_nongw.sh

diff --git a/tools/testing/selftests/net/Makefile b/tools/testing/selftests/net/Makefile
index ddad703ace34..db05b3764b77 100644
--- a/tools/testing/selftests/net/Makefile
+++ b/tools/testing/selftests/net/Makefile
@@ -11,7 +11,7 @@ TEST_PROGS += udpgso_bench.sh fib_rule_tests.sh msg_zerocopy.sh psock_snd.sh
 TEST_PROGS += udpgro_bench.sh udpgro.sh test_vxlan_under_vrf.sh reuseport_addr_any.sh
 TEST_PROGS += test_vxlan_fdb_changelink.sh so_txtime.sh ipv6_flowlabel.sh
 TEST_PROGS += tcp_fastopen_backup_key.sh fcnal-test.sh l2tp.sh traceroute.sh
-TEST_PROGS += fin_ack_lat.sh fib_nexthop_multiprefix.sh fib_nexthops.sh
+TEST_PROGS += fin_ack_lat.sh fib_nexthop_multiprefix.sh fib_nexthops.sh fib_nexthop_nongw.sh
 TEST_PROGS += altnames.sh icmp.sh icmp_redirect.sh ip6_gre_headroom.sh
 TEST_PROGS += route_localnet.sh
 TEST_PROGS += reuseaddr_ports_exhausted.sh
diff --git a/tools/testing/selftests/net/fib_nexthop_nongw.sh b/tools/testing/selftests/net/fib_nexthop_nongw.sh
new file mode 100755
index 000000000000..b7b928b38ce4
--- /dev/null
+++ b/tools/testing/selftests/net/fib_nexthop_nongw.sh
@@ -0,0 +1,119 @@
+#!/bin/bash
+# SPDX-License-Identifier: GPL-2.0
+#
+# ns: h1               | ns: h2
+#   192.168.0.1/24     |
+#            eth0      |
+#                      |       192.168.1.1/32
+#            veth0 <---|---> veth1
+# Validate source address selection for route without gateway
+
+PAUSE_ON_FAIL=no
+VERBOSE=0
+ret=0
+
+################################################################################
+# helpers
+
+log_test()
+{
+	local rc=$1
+	local expected=$2
+	local msg="$3"
+
+	if [ ${rc} -eq ${expected} ]; then
+		printf "TEST: %-60s  [ OK ]\n" "${msg}"
+		nsuccess=$((nsuccess+1))
+	else
+		ret=1
+		nfail=$((nfail+1))
+		printf "TEST: %-60s  [FAIL]\n" "${msg}"
+		if [ "${PAUSE_ON_FAIL}" = "yes" ]; then
+			echo
+			echo "hit enter to continue, 'q' to quit"
+			read a
+			[ "$a" = "q" ] && exit 1
+		fi
+	fi
+
+	[ "$VERBOSE" = "1" ] && echo
+}
+
+run_cmd()
+{
+	local cmd="$*"
+	local out
+	local rc
+
+	if [ "$VERBOSE" = "1" ]; then
+		echo "COMMAND: $cmd"
+	fi
+
+	out=$(eval $cmd 2>&1)
+	rc=$?
+	if [ "$VERBOSE" = "1" -a -n "$out" ]; then
+		echo "$out"
+	fi
+
+	[ "$VERBOSE" = "1" ] && echo
+
+	return $rc
+}
+
+################################################################################
+# config
+setup()
+{
+	ip netns add h1
+	ip -n h1 link set lo up
+	ip netns add h2
+	ip -n h2 link set lo up
+
+	# Add a fake eth0 to support an ip address
+	ip -n h1 link add name eth0 type dummy
+	ip -n h1 link set eth0 up
+	ip -n h1 address add 192.168.0.1/24 dev eth0
+
+	# Configure veths (same @mac, arp off)
+	ip -n h1 link add name veth0 type veth peer name veth1 netns h2
+	ip -n h1 link set veth0 up
+
+	ip -n h2 link set veth1 up
+
+	# Configure @IP in the peer netns
+	ip -n h2 address add 192.168.1.1/32 dev veth1
+	ip -n h2 route add default dev veth1
+
+	# Add a nexthop without @gw and use it in a route
+	ip -n h1 nexthop add id 1 dev veth0
+	ip -n h1 route add 192.168.1.1 nhid 1
+}
+
+cleanup()
+{
+	ip netns del h1 2>/dev/null
+	ip netns del h2 2>/dev/null
+}
+
+trap cleanup EXIT
+
+################################################################################
+# main
+
+while getopts :pv o
+do
+	case $o in
+		p) PAUSE_ON_FAIL=yes;;
+		v) VERBOSE=1;;
+	esac
+done
+
+cleanup
+setup
+
+run_cmd ip -netns h1 route get 192.168.1.1
+log_test $? 0 "nexthop: get route with nexthop without gw"
+run_cmd ip netns exec h1 ping -c1 192.168.1.1
+log_test $? 0 "nexthop: ping through nexthop without gw"
+
+exit $ret
-- 
2.33.0

Re: [PATCH net v3 1/2] ip: fix dflt addr selection for connected nexthop

[patchwork-bot+netdevbpf]

Hello:

This series was applied to netdev/net.git (master)
by Paolo Abeni <pabeni@redhat.com>:

On Wed, 13 Jul 2022 13:48:52 +0200 you wrote:
> When a nexthop is added, without a gw address, the default scope was set
> to 'host'. Thus, when a source address is selected, 127.0.0.1 may be chosen
> but rejected when the route is used.
> 
> When using a route without a nexthop id, the scope can be configured in the
> route, thus the problem doesn't exist.
> 
> [...]

Here is the summary with links:
  - [net,v3,1/2] ip: fix dflt addr selection for connected nexthop
    https://git.kernel.org/netdev/net/c/747c14307214
  - [net,v3,2/2] selftests/net: test nexthop without gw
    https://git.kernel.org/netdev/net/c/cd72e61bad14

You are awesome, thank you!
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