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ipv4: Honor "ignore_routes_with_linkdown" sysctl in nexthop selection

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Commit 32607a332c ("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 <idosch@nvidia.com>
Reviewed-by: Willem de Bruijn <willemb@google.com>
Reviewed-by: David Ahern <dsahern@kernel.org>
Signed-off-by: David S. Miller <davem@davemloft.net>
This commit is contained in:
Ido Schimmel
2025-04-30 13:02:40 +03:00
committed by David S. Miller
parent 586ceac9ac
commit 836b313a14
1 changed files with 9 additions and 2 deletions
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11
net/ipv4/fib_semantics.c
View File

@@ -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) {