On Wed, Sep 30, 2026 at 11:22:28AM -0400, [email protected] wrote: > From: Hengyu Liang <[email protected]> > > ip6_route_info_create_nh() promotes routes that use the loopback device > as their nexthop device to reject routes, except for local and anycast > routes and routes to the loopback address, as true routes via the > loopback device would result in kernel looping. > > Before commit 21ec92774d15 ("net: ipv6: fix panic when IPv4 route > references loopback IPv6 nexthop"), fib6_nh_init() also treated these > routes as reject routes, so it neither validated their gateway nor > checked the state of the loopback device. That commit restricted the > check in fib6_nh_init() to explicit reject routes to fix IPv6 nexthop > objects that use the loopback device. As a side effect, the nexthop of a > route via the loopback device is now validated like the nexthop of a > regular route before the route is promoted to a reject route, and adding > such a route fails in cases that used to work: > > # ip link set dev lo down > # ip -6 route add 2001:db8::/32 dev lo > Error: Nexthop device is not up.
Consistent with IPv4 and expected: # ip link set dev lo down # ip route add 192.0.2.0/24 dev lo Error: Device for nexthop is not up. > # ip link set dev lo up > # ip -6 route add 2001:db8::/32 via 2001:db8:1::1 dev lo > RTNETLINK answers: No route to host > # ip -6 route add default via ::ffff:192.0.2.1 dev lo > RTNETLINK answers: No route to host Likewise: # ip link set dev lo up # ip route add 192.0.2.0/24 via 198.51.100.1 dev lo Error: Nexthop has invalid gateway. > # sysctl -qw net.ipv6.conf.lo.disable_ipv6=1 > # ip -6 route add 2001:db8::/32 dev lo > Error: IPv6 is disabled on nexthop device. Inapplicable, but expected. I don't understand what motivated this series.
