The fullmesh flag mustn't be used with the signal flag when adding an
address. Commands like this should be treated as invalid commands:

 ip mptcp endpoint add 10.0.2.1 signal fullmesh

This patch added the necessary flags check for this case.

Acked-by: Mat Martineau <mathew.j.martineau@linux.intel.com>
Signed-off-by: Geliang Tang <geliang.tang@suse.com>
---
 ip/ipmptcp.c | 5 +++++
 1 file changed, 5 insertions(+)

diff --git a/ip/ipmptcp.c b/ip/ipmptcp.c
index eef7c6f4..0b744720 100644
--- a/ip/ipmptcp.c
+++ b/ip/ipmptcp.c
@@ -116,6 +116,11 @@ static int mptcp_parse_opt(int argc, char **argv, struct nlmsghdr *n, int cmd)
 	ll_init_map(&rth);
 	while (argc > 0) {
 		if (get_flags(*argv, &flags) == 0) {
+			if (adding &&
+			    (flags & MPTCP_PM_ADDR_FLAG_SIGNAL) &&
+			    (flags & MPTCP_PM_ADDR_FLAG_FULLMESH))
+				invarg("invalid flags\n", *argv);
+
 			/* allow changing the 'backup' flag only */
 			if (cmd == MPTCP_PM_CMD_SET_FLAGS &&
 			    (flags & ~MPTCP_PM_ADDR_FLAG_BACKUP))
-- 
2.34.1

On Wed, 23 Feb 2022 10:59:47 +0800
Geliang Tang <geliang.tang@suse.com> wrote:

> +			if (adding &&
> +			    (flags & MPTCP_PM_ADDR_FLAG_SIGNAL) &&
> +			    (flags & MPTCP_PM_ADDR_FLAG_FULLMESH))
> +				invarg("invalid flags\n", *argv)

There is a duplicate newline here, the message already gets newline from invarg().
If possible could you give explanation to the user.

Looks like mptcp has this in lots of places, and would be helpful
to give better response.