router: always use link-local src address for RAs

This is a follow-up to:
https://github.com/openwrt/odhcpd/pull/242

As noted by @willmo [1], RAs are currently not strictly limited to using a
link-local source address, which they should according to RFC4861, §4.2.

This is usually not an issue, since router solicitations typically
originate from link-local source addresses or the undefined address,
meaning that odhcpd will reply with its own link-local address
(auto-selected by the kernel).

But if a solicitation is sent from e.g. a GUA/ULA address, odhpcd will
currently reply using it's own GUA/ULA address.

While fixing this, correct some misleading comments.

[1] https://github.com/openwrt/odhcpd/pull/242#issuecomment-3475020864

Signed-off-by: David Härdeman <[email protected]>
Link: https://github.com/openwrt/odhcpd/pull/297
Signed-off-by: Álvaro Fernández Rojas <[email protected]>

diff --git a/src/router.c b/src/router.c
index 9b482d2d9dcab45774728644062bc227a642394f..46b6ce4ffecc87b7a9f939941efef671d15604e2 100644 (file)
--- a/src/router.c
+++ b/src/router.c
@@ -1002,7 +1002,7 @@ static int send_router_advert(struct interface *iface, const struct in6_addr *fr
 
        debug("Sending a RA on %s", iface->name);
 
-       if (odhcpd_send(iface->router_event.uloop.fd, &dest, iov, ARRAY_SIZE(iov), iface) > 0) {
+       if (odhcpd_try_send_with_src(iface->router_event.uloop.fd, &dest, iov, ARRAY_SIZE(iov), iface) > 0) {
                iface->ra_sent++;
 
                config_save_ra_pio(iface);
@@ -1056,7 +1056,7 @@ static void handle_icmpv6(void *addr, void *data, size_t len,
 }
 
 
-/* Forward router solicitation */
+/* Forward a router solicitation from slave to master interface */
 static void forward_router_solicitation(const struct interface *iface)
 {
        struct icmp6_hdr rs = {ND_ROUTER_SOLICIT, 0, 0, {{0}}};
@@ -1076,7 +1076,7 @@ static void forward_router_solicitation(const struct interface *iface)
 }
 
 
-/* Handler for incoming router solicitations on slave interfaces */
+/* Forward a router advertisment from master to slave interfaces */
 static void forward_router_advertisement(const struct interface *iface, uint8_t *data, size_t len)
 {
        struct nd_router_advert *adv = (struct nd_router_advert *)data;