[PATCH mptcp-net v3 4/8] mptcp: pm: userspace: allow announcing ID0 addr

It is valid to announce an address with the ID0, the in-kernel PM allows
to do that when re-announcing the initial IP address after having been
deleted.

So no need to have such exception. If the ID is set to 0, but the
address doesn't match with the existing one, an error will be returned
by mptcp_userspace_pm_append_new_local_addr().

Note that once removed, the ID0 entry could be replaced by another IP
address. The RFC8684 doesn't specify this specific case with ID0, but it
says [1]: "A host wishing to replace an existing Address ID MUST first
remove the existing one". In these unclear conditions, better to let the
responsibility to the userspace daemon to pick the same IP or another
one, similar to what was in place before.

Fixes: 9ab4807c84a4 ("mptcp: netlink: Add MPTCP_PM_CMD_ANNOUNCE")
Link: https://datatracker.ietf.org/doc/html/rfc8684#section-3.4.1-13 [1]
Signed-off-by: Matthieu Baerts (NGI0) <[email protected]>
---
v2: Add note about re-using the ID0 with another address (Sashiko)
---
 net/mptcp/pm_userspace.c | 6 ------
 1 file changed, 6 deletions(-)

diff --git a/net/mptcp/pm_userspace.c b/net/mptcp/pm_userspace.c
index 27fed3519d39..2c13c6273ad3 100644
--- a/net/mptcp/pm_userspace.c
+++ b/net/mptcp/pm_userspace.c
@@ -236,12 +236,6 @@ int mptcp_pm_nl_announce_doit(struct sk_buff *skb, struct genl_info *info)
 	if (err < 0)
 		goto announce_err;
 
-	if (addr_val.addr.id == 0) {
-		NL_SET_ERR_MSG_ATTR(info->extack, addr, "invalid addr id");
-		err = -EINVAL;
-		goto announce_err;
-	}
-
 	if (!(addr_val.flags & MPTCP_PM_ADDR_FLAG_SIGNAL)) {
 		NL_SET_ERR_MSG_ATTR(info->extack, addr, "invalid addr flags");
 		err = -EINVAL;

-- 
2.53.0