[PATCH netifd] interface-ip: Normalise prefix address using netmask before using it

[Daniel Gröber]

When a proto registers a prefix with an address which has bits outside the
netmask set this confuses the prefix-assignment code further down the line.

For example if we have an interface with

    option ip6prefix fdff:ffff:ffff:ffff::1/48

and a couple with

    option ip6assign 64

then all these interfaces will be assigned fdff:ffff:ffff:ffff::1/64 which
is obviously wrong, they should at least have unique prefixes.

What is happening here is that we simply OR the calculated assignment part
into the address in interface_set_prefix_address:961, like so:

    addr.addr.in6.s6_addr32[1] |= htonl(assignment->assigned);

but we never masked the host address bits out of the address after parsing
it using inet_pton. To fix this we simply mask away the host bits in the
address before using it.

Signed-off-by: Daniel Gröber <dxld at darkboxed.org>
---
 interface-ip.c | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/interface-ip.c b/interface-ip.c
index 6efc3c5..e8f2dbd 100644
--- a/interface-ip.c
+++ b/interface-ip.c
@@ -1294,6 +1294,8 @@ interface_ip_add_device_prefix(struct interface *iface, struct in6_addr *addr,
 	prefix->iface = iface;
 	INIT_LIST_HEAD(&prefix->assignments);
 
+	clear_if_addr((union if_addr *)&prefix->addr, prefix->length);
+
 	if (excl_addr) {
 		prefix->excl_addr = *excl_addr;
 		prefix->excl_length = excl_length;
-- 
2.20.1