After deleting an IPv6 address on an interface and cleaning up the
related preferred source entries, it is important to ensure that all
routes associated with the deleted address are properly cleared. The
current implementation of rt6_remove_prefsrc() only checks the preferred
source addresses bound to the current device. However, there may be
routes that are bound to other devices but still utilize the same
preferred source address.

To address this issue, it is necessary to also delete entries that are
bound to other interfaces but share the same source address with the
current device. Failure to delete these entries would leave routes that
are bound to the deleted address unclear. Here is an example reproducer
(I have omitted unrelated routes):

+ ip link add dummy1 type dummy
+ ip link add dummy2 type dummy
+ ip link set dummy1 up
+ ip link set dummy2 up
+ ip addr add 1:2:3:4::5/64 dev dummy1
+ ip route add 7:7:7:0::1 dev dummy1 src 1:2:3:4::5
+ ip route add 7:7:7:0::2 dev dummy2 src 1:2:3:4::5
+ ip -6 route show
1:2:3:4::/64 dev dummy1 proto kernel metric 256 pref medium
7:7:7::1 dev dummy1 src 1:2:3:4::5 metric 1024 pref medium
7:7:7::2 dev dummy2 src 1:2:3:4::5 metric 1024 pref medium
+ ip addr del 1:2:3:4::5/64 dev dummy1
+ ip -6 route show
7:7:7::1 dev dummy1 metric 1024 pref medium
7:7:7::2 dev dummy2 src 1:2:3:4::5 metric 1024 pref medium

As Ido reminds, in IPv6, the preferred source address is looked up in
the same VRF as the first nexthop device, which is different with IPv4.
So, while removing the device checking, we also need to add an
ipv6_chk_addr() check to make sure the address does not exist on the other
devices of the rt nexthop device's VRF.

After fix:
+ ip addr del 1:2:3:4::5/64 dev dummy1
+ ip -6 route show
7:7:7::1 dev dummy1 metric 1024 pref medium
7:7:7::2 dev dummy2 metric 1024 pref medium
Reported-by: Thomas Haller <thaller@redhat.com>
Closes: https://bugzilla.redhat.com/show_bug.cgi?id=2170513Reviewed-by: Ido Schimmel <idosch@nvidia.com>
Signed-off-by: Hangbin Liu <liuhangbin@gmail.com>
Reviewed-by: David Ahern <dsahern@kernel.org>
Signed-off-by: David S. Miller <davem@davemloft.net>