mptcp: pm: userspace: flags: clearer msg if no remote addr

Since its introduction in commit 892f396 ("mptcp: netlink: issue
MP_PRIO signals from userspace PMs"), it was mandatory to specify the
remote address, because of the 'if (rem->addr.family == AF_UNSPEC)'
check done later one.

In theory, this attribute can be optional, but it sounds better to be
precise to avoid sending the MP_PRIO on the wrong subflow, e.g. if there
are multiple subflows attached to the same local ID. This can be relaxed
later on if there is a need to act on multiple subflows with one
command.

For the moment, the check to see if attr_rem is NULL can be removed,
because mptcp_pm_parse_entry() will do this check as well, no need to do
that differently here.

While at it, move the parsing after the check linked to the local
attribute.

Signed-off-by: Matthieu Baerts (NGI0) <[email protected]>

Author: matttbe

net/mptcp/pm_userspace.c

@@ -601,19 +601,17 @@ int mptcp_userspace_pm_set_flags(struct sk_buff *skb, struct genl_info *info)
 	if (ret < 0)
 		goto set_flags_err;
 
-	if (attr_rem) {
-		ret = mptcp_pm_parse_entry(attr_rem, info, false, &rem);
-		if (ret < 0)
-			goto set_flags_err;
-	}
-
 	if (loc.addr.family == AF_UNSPEC) {
 		NL_SET_ERR_MSG_ATTR(info->extack, attr,
 				    "invalid local address family");
 		ret = -EINVAL;
 		goto set_flags_err;
 	}
 
+	ret = mptcp_pm_parse_entry(attr_rem, info, false, &rem);
+	if (ret < 0)
+		goto set_flags_err;
+
 	if (rem.addr.family == AF_UNSPEC) {
 		NL_SET_ERR_MSG_ATTR(info->extack, attr_rem,
 				    "invalid remote address family");