From: Nicolas Dichtel nicolas.dichtel@6wind.com

BugLink: https://bugs.launchpad.net/bugs/1988809

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 Link: https://lore.kernel.org/r/20220713114853.29406-1-nicolas.dichtel@6wind.com Signed-off-by: Paolo Abeni pabeni@redhat.com (backported from commit 747c14307214b55dbd8250e1ab44cad8305756f1) [lukenow: use dev_hold instead of dev_hold_track as dev_hold_track requires some debugging infastructure that we don't want to backport] Signed-off-by: Luke Nowakowski-Krijger luke.nowakowskikrijger@canonical.com --- 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 f99ad4a98907d..16fe034615635 100644 --- a/net/ipv4/fib_semantics.c +++ b/net/ipv4/fib_semantics.c @@ -1217,7 +1217,7 @@ static int fib_check_nh_nongw(struct net *net, struct fib_nh *nh,

nh->fib_nh_dev = in_dev->dev; dev_hold(nh->fib_nh_dev); - 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;