6.18-stable review patch. If anyone has any objections, please let me know.
------------------
From: Vadim Fedorenko vadim.fedorenko@linux.dev
[ Upstream commit 6e17474aa9fe15015c9921a5081c7ca71783aac6 ]
Preference of nexthop with source address broke ECMP for packets with source addresses which are not in the broadcast domain, but rather added to loopback/dummy interfaces. Original behaviour was to balance over nexthops while now it uses the latest nexthop from the group. To fix the issue introduce next hop scoring system where next hops with source address equal to requested will always have higher priority.
For the case with 198.51.100.1/32 assigned to dummy0 and routed using 192.0.2.0/24 and 203.0.113.0/24 networks:
2: dummy0: <BROADCAST,NOARP,UP,LOWER_UP> mtu 1500 qdisc noqueue state UNKNOWN group default qlen 1000 link/ether d6:54:8a:ff:78:f5 brd ff:ff:ff:ff:ff:ff inet 198.51.100.1/32 scope global dummy0 valid_lft forever preferred_lft forever 7: veth1@if6: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc noqueue state UP group default qlen 1000 link/ether 06:ed:98:87:6d:8a brd ff:ff:ff:ff:ff:ff link-netnsid 0 inet 192.0.2.2/24 scope global veth1 valid_lft forever preferred_lft forever inet6 fe80::4ed:98ff:fe87:6d8a/64 scope link proto kernel_ll valid_lft forever preferred_lft forever 9: veth3@if8: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc noqueue state UP group default qlen 1000 link/ether ae:75:23:38:a0:d2 brd ff:ff:ff:ff:ff:ff link-netnsid 0 inet 203.0.113.2/24 scope global veth3 valid_lft forever preferred_lft forever inet6 fe80::ac75:23ff:fe38:a0d2/64 scope link proto kernel_ll valid_lft forever preferred_lft forever
~ ip ro list: default nexthop via 192.0.2.1 dev veth1 weight 1 nexthop via 203.0.113.1 dev veth3 weight 1 192.0.2.0/24 dev veth1 proto kernel scope link src 192.0.2.2 203.0.113.0/24 dev veth3 proto kernel scope link src 203.0.113.2
before: for i in {1..255} ; do ip ro get 10.0.0.$i; done | grep veth | awk ' {print $(NF-2)}' | sort | uniq -c: 255 veth3
after: for i in {1..255} ; do ip ro get 10.0.0.$i; done | grep veth | awk ' {print $(NF-2)}' | sort | uniq -c: 122 veth1 133 veth3
Fixes: 32607a332cfe ("ipv4: prefer multipath nexthop that matches source address") Signed-off-by: Vadim Fedorenko vadim.fedorenko@linux.dev Reviewed-by: Ido Schimmel idosch@nvidia.com Reviewed-by: Willem de Bruijn willemb@google.com Link: https://patch.msgid.link/20251221192639.3911901-1-vadim.fedorenko@linux.dev Signed-off-by: Paolo Abeni pabeni@redhat.com Signed-off-by: Sasha Levin sashal@kernel.org --- net/ipv4/fib_semantics.c | 26 ++++++++++---------------- 1 file changed, 10 insertions(+), 16 deletions(-)
diff --git a/net/ipv4/fib_semantics.c b/net/ipv4/fib_semantics.c index a5f3c8459758..0caf38e44c73 100644 --- a/net/ipv4/fib_semantics.c +++ b/net/ipv4/fib_semantics.c @@ -2167,8 +2167,8 @@ void fib_select_multipath(struct fib_result *res, int hash, { struct fib_info *fi = res->fi; struct net *net = fi->fib_net; - bool found = false; bool use_neigh; + int score = -1; __be32 saddr;
if (unlikely(res->fi->nh)) { @@ -2180,7 +2180,7 @@ void fib_select_multipath(struct fib_result *res, int hash, saddr = fl4 ? fl4->saddr : 0;
change_nexthops(fi) { - int nh_upper_bound; + int nh_upper_bound, nh_score = 0;
/* Nexthops without a carrier are assigned an upper bound of * minus one when "ignore_routes_with_linkdown" is set. @@ -2190,24 +2190,18 @@ void fib_select_multipath(struct fib_result *res, int hash, (use_neigh && !fib_good_nh(nexthop_nh))) continue;
- if (!found) { + if (saddr && nexthop_nh->nh_saddr == saddr) + nh_score += 2; + if (hash <= nh_upper_bound) + nh_score++; + if (score < nh_score) { res->nh_sel = nhsel; res->nhc = &nexthop_nh->nh_common; - found = !saddr || nexthop_nh->nh_saddr == saddr; + if (nh_score == 3 || (!saddr && nh_score == 1)) + return; + score = nh_score; }
- if (hash > nh_upper_bound) - continue; - - if (!saddr || nexthop_nh->nh_saddr == saddr) { - res->nh_sel = nhsel; - res->nhc = &nexthop_nh->nh_common; - return; - } - - if (found) - return; - } endfor_nexthops(fi); } #endif