[PATCH 5/5] dhcp6: Don't require Client ID in Information-request reply

Since we don't include our Client ID option when sending an
Information-request, the server can't send it back in its Reply.  Don't
require it when validating.
RFC 8415 Section 18.2.6 has this to say about the Client ID:

"The client SHOULD include a Client Identifier option (see Section 21.2)
to identify itself to the server (however, see Section 4.3.1 of [RFC7844]
for reasons why a client may not want to include this option).  If the
client does not include a Client Identifier option, the server will not
be able to return any client-specific options to the client, or the
server may choose not to respond to the message at all."

RFC 7833 Section 4.3.1 says this:
"When using stateless DHCPv6, clients wanting to protect their privacy
SHOULD NOT include client identifiers in their Information-request
messages.  This will prevent the server from specifying client-specific
options if it is configured to do so, but the need for anonymity
precludes such options anyway."
---
 ell/dhcp6.c | 13 ++++++++++---
 1 file changed, 10 insertions(+), 3 deletions(-)

diff --git a/ell/dhcp6.c b/ell/dhcp6.c
index 3dbd0cd..a17dc49 100644
--- a/ell/dhcp6.c
+++ b/ell/dhcp6.c
@@ -1098,6 +1098,7 @@ bool _dhcp6_option_iter_next(struct dhcp6_option_iter *iter, uint16_t *type,
 }
 
 static int dhcp6_client_validate_message(struct l_dhcp6_client *client,
+					bool expect_client_id,
 					const struct dhcp6_message *message,
 					size_t len)
 {
@@ -1205,7 +1206,7 @@ static int dhcp6_client_validate_message(struct l_dhcp6_client *client,
 		}
 	}
 
-	if (!duid_verified) {
+	if (expect_client_id && !duid_verified) {
 		CLIENT_DEBUG("Message %s - no client id option found", mstr);
 		return -EBADMSG;
 	}
@@ -1229,7 +1230,7 @@ static int dhcp6_client_receive_advertise(struct l_dhcp6_client *client,
 	if (advertise->msg_type != DHCP6_MESSAGE_TYPE_ADVERTISE)
 		return -EINVAL;
 
-	r = dhcp6_client_validate_message(client, advertise, len);
+	r = dhcp6_client_validate_message(client, true, advertise, len);
 	if (r < 0)
 		return r;
 
@@ -1311,11 +1312,17 @@ static int dhcp6_client_receive_reply(struct l_dhcp6_client *client,
 	struct l_dhcp6_lease *lease;
 	struct dhcp6_option_iter iter;
 	int r;
+	/*
+	 * Per RFC 7844 Section 4.3.1 we never send Client ID options in
+	 * Information-requests so don't expect the replies to contain them.
+	 */
+	bool expect_client_id =
+		(client->state != DHCP6_STATE_REQUESTING_INFORMATION);
 
 	if (reply->msg_type != DHCP6_MESSAGE_TYPE_REPLY)
 		return -EINVAL;
 
-	r = dhcp6_client_validate_message(client, reply, len);
+	r = dhcp6_client_validate_message(client, expect_client_id, reply, len);
 	if (r < 0)
 		return r;
 
-- 
2.34.1