In the Linux kernel, the following vulnerability has been resolved:ipv6: release nexthop on device removalThe CI is hitting some aperiodic hangup at device removal time in thepmtu.sh self-test:unregister_netdevice: waiting for veth_A-R1 to become free. Usage count = 6ref_tracker: veth_A-R1@ffff888013df15d8 has 1/5 users at dst_init+0x84/0x4a0 dst_alloc+0x97/0x150 ip6_dst_alloc+0x23/0x90 ip6_rt_pcpu_alloc+0x1e6/0x520 ip6_pol_route+0x56f/0x840 fib6_rule_lookup+0x334/0x630 ip6_route_output_flags+0x259/0x480 ip6_dst_lookup_tail.constprop.0+0x5c2/0x940 ip6_dst_lookup_flow+0x88/0x190 udp_tunnel6_dst_lookup+0x2a7/0x4c0 vxlan_xmit_one+0xbde/0x4a50 [vxlan] vxlan_xmit+0x9ad/0xf20 [vxlan] dev_hard_start_xmit+0x10e/0x360 __dev_queue_xmit+0xf95/0x18c0 arp_solicit+0x4a2/0xe00 neigh_probe+0xaa/0xf0While the first suspect is the dst_cache, explicitly tracking the dstowing the last device reference via probes proved such dst is held bythe nexthop in the originating fib6_info.Similar to commit f5b51fe804ec ("ipv6: route: purge exception onremoval"), we need to explicitly release the originating fib info whendisconnecting a to-be-removed device from a live ipv6 dst: move thefib6_info cleanup into ip6_dst_ifdown().Tested running:./pmtu.sh cleanup_ipv6_exceptionin a tight loop for more than 400 iterations with no spat, running anunpatched kernel I observed a splat every ~10 iterations.
