IPv6 and rt6_lookup()

Hello,

Suppose that a host has autoconfiguration enabled. It will take RA to autoconfigure an IPv6 address. For example, 2001:0db8:3008:c1ca:2d0:b7ff:febb:4aee/64.
This host will create a route entry for this onlink prefix (dst:
2001:0db8:3008:c1ca::/64)
in the MAIN table with the lifetime present in prefix option in RA. Each time this host will receive a RA, it will update this lifetime. To do this,
it will call rt6_lookup() (in addrconf_prefix_rcv()) to find the entry.

Now, suppose that our host joins this anycast group:
"2001:0db8:3008:c1ca::0". A route

entry will be added in the LOCAL table (see addrconf_join_anycast()). Problem is that, next time our host will receive a RA and will perform a rt6_lookup(),
this function will return the local entry (LOCAL table), and not the "dynamic" entry
(MAIN table). Consequence is that the lifetime of the dynamic entry will never been updated,
and so will expire, whereas the host will keep the corresponding address.

Maybe, when strict is set to 1 in rt6_lookup(), kernel must not return an anycast route.
What about this patch ?

Regards,
Nicolas

[IPv6] Don't return anycast route when strict is enable

Signed-off-by Nicolas DICHTEL <[email protected]>

------------------------------------------------------------------------

net/ipv6/route.c +2 -0

index c953466..51a8c1d 100644
@@ -248,6 +248,8 @@ static __inline__ struct rt6_info *rt6_d
 			if (dev->ifindex == oif)
 				return sprt;
 			if (dev->flags & IFF_LOOPBACK) {
+				if (strict && sprt->rt6i_flags & RTF_ANYCAST)
+					continue;
 				if (sprt->rt6i_idev == NULL ||
 				    sprt->rt6i_idev->dev->ifindex != oif) {
 					if (strict && oif)

Quoted 12 lines · Nicolas DICHTEL

Hello,

Suppose that a host has autoconfiguration enabled. It will take RA to autoconfigure an IPv6 address. For example, 2001:0db8:3008:c1ca:2d0:b7ff:febb:4aee/64.
This host will create a route entry for this onlink prefix (dst:
2001:0db8:3008:c1ca::/64)
in the MAIN table with the lifetime present in prefix option in RA. Each time this host will receive a RA, it will update this lifetime. To do this,
it will call rt6_lookup() (in addrconf_prefix_rcv()) to find the entry.

Quoted 2 lines

Now, suppose that our host joins this anycast group:
"2001:0db8:3008:c1ca::0". A route

Hmm... you are configuring a subnet router anycast address on host and the implementation lets you do it? That's not good. I don't think you sould be permitted to configure a subnet router anycast address
on a host that autoconfigures it's interface.