Hi again,
I've done some pretty in depth debugging now to determine exactly what
the behavior of ipv6_stub->ipv6_dst_lookup is. First I'll start with
ip_route_output_flow, which I believe to be well behaved, and then
I'll show ipv6_stub->ipv6_dst_lookup, which seems ill-behaved:
Userspace:
ip addr add 192.168.1.2/24 dev eth0
Kernelspace:
struct flowi4 fl = {
.saddr = 192.168.1.2,
.daddr = 192.168.1.99,
};
rt = ip_route_output_flow(sock_net(sock), &fl, sock);
// rt returns valid rt for routing to 192.168.1.99 from
192.168.1.2 using eth0
Userspace:
ip addr add 192.168.1.3/24 dev eth0
ip addr del 192.168.1.2/24 dev eth0
Kernelspace:
struct flowi4 fl = {
.saddr = 192.168.1.2,
.daddr = 192.168.1.99,
};
rt = ip_route_output_flow(sock_net(sock), &fl, sock);
// PTR_ERR(rt) == -EINVAL
This seems correct behavior to me, since no interface has 192.168.1.2
as a source address.
Now for the incorrect IPv6 behavior:
Userspace:
ip -6 addr add abcd::2/96 dev eth0
Kernelspace:
struct flowi6 fl = {
.saddr = abcd::2,
.daddr = abcd::99,
};
ret = ipv6_stub->ipv6_dst_lookup(sock_net(sock), sock, &dst, &fl);
// ret is 0, and dst is a non-null dst routing to abcd::99 from
abcd::2 using eth0
Userspace:
ip -6 addr add abcd::3/96 dev eth0
ip -6 addr del abcd::2/96 dev eth0
Kernelspace:
struct flowi6 fl = {
.saddr = abcd::2,
.daddr = abcd::99,
};
ret = ipv6_stub->ipv6_dst_lookup(sock_net(sock), sock, &dst, &fl);
// ret is 0, and dst is a non-null dst routing to abcd::99 from
abcd::2 using eth0 **INCORRECT BEHAVIOR!**
This seems *INCORRECT* behavior to me, since no interface has abcd::2
as a source address.
So, to summarize, the problem is that ipv6_dst_lookup will happily
return a dst even though the source IP has been removed from the
interface.
I hope this clarifies things. I await your response.
Regards,
Jason
