From: Ido Schimmel Date: Wed, 30 Apr 2025 10:02:40 +0000 (+0300) Subject: ipv4: Honor "ignore_routes_with_linkdown" sysctl in nexthop selection X-Git-Url: https://www.infradead.org/git/?a=commitdiff_plain;h=6.15.0-rc4-syzkaller-00746-g836b313a14a3;p=users%2Fjedix%2Flinux-maple.git ipv4: Honor "ignore_routes_with_linkdown" sysctl in nexthop selection Commit 32607a332cfe ("ipv4: prefer multipath nexthop that matches source address") changed IPv4 nexthop selection to prefer a nexthop whose nexthop device is assigned the specified source address for locally generated traffic. While the selection honors the "fib_multipath_use_neigh" sysctl and will not choose a nexthop with an invalid neighbour, it does not honor the "ignore_routes_with_linkdown" sysctl and can choose a nexthop without a carrier: $ sysctl net.ipv4.conf.all.ignore_routes_with_linkdown net.ipv4.conf.all.ignore_routes_with_linkdown = 1 $ ip route show 198.51.100.0/24 198.51.100.0/24 nexthop via 192.0.2.2 dev dummy1 weight 1 nexthop via 192.0.2.18 dev dummy2 weight 1 dead linkdown $ ip route get 198.51.100.1 from 192.0.2.17 198.51.100.1 from 192.0.2.17 via 192.0.2.18 dev dummy2 uid 0 Solve this by skipping over nexthops whose assigned hash upper bound is minus one, which is the value assigned to nexthops that do not have a carrier when the "ignore_routes_with_linkdown" sysctl is set. In practice, this probably does not matter a lot as the initial route lookup for the source address would not choose a nexthop that does not have a carrier in the first place, but the change does make the code clearer. Signed-off-by: Ido Schimmel Reviewed-by: Willem de Bruijn Reviewed-by: David Ahern Signed-off-by: David S. Miller --- diff --git a/net/ipv4/fib_semantics.c b/net/ipv4/fib_semantics.c index 03959c60d128..dabe2b7044ab 100644 --- a/net/ipv4/fib_semantics.c +++ b/net/ipv4/fib_semantics.c @@ -2188,7 +2188,14 @@ void fib_select_multipath(struct fib_result *res, int hash, saddr = fl4 ? fl4->saddr : 0; change_nexthops(fi) { - if (use_neigh && !fib_good_nh(nexthop_nh)) + int nh_upper_bound; + + /* Nexthops without a carrier are assigned an upper bound of + * minus one when "ignore_routes_with_linkdown" is set. + */ + nh_upper_bound = atomic_read(&nexthop_nh->fib_nh_upper_bound); + if (nh_upper_bound == -1 || + (use_neigh && !fib_good_nh(nexthop_nh))) continue; if (!found) { @@ -2197,7 +2204,7 @@ void fib_select_multipath(struct fib_result *res, int hash, found = !saddr || nexthop_nh->nh_saddr == saddr; } - if (hash > atomic_read(&nexthop_nh->fib_nh_upper_bound)) + if (hash > nh_upper_bound) continue; if (!saddr || nexthop_nh->nh_saddr == saddr) {