tipc: fix message importance range check

Commit 3b4f302d ("tipc: eliminate
redundant locking") introduced a bug by removing the sanity check
for message importance, allowing programs to assign any value to
the msg_user field. This will mess up the packet reception logic
and may cause random link resets.
Signed-off-by: NErik Hugne <erik.hugne@ericsson.com>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>

net/tipc/port.h

@@ -179,8 +179,10 @@ static inline int tipc_port_importance(struct tipc_port *port)
 	return msg_importance(&port->phdr);
 }
 
-static inline void tipc_port_set_importance(struct tipc_port *port, int imp)
+static inline int tipc_port_set_importance(struct tipc_port *port, int imp)
 {
+	if (imp > TIPC_CRITICAL_IMPORTANCE)
+		return -EINVAL
 	msg_set_importance(&port->phdr, (u32)imp);
 }
 

net/tipc/socket.c

@@ -1973,7 +1973,7 @@ static int tipc_setsockopt(struct socket *sock, int lvl, int opt,
 
 	switch (opt) {
 	case TIPC_IMPORTANCE:
-		tipc_port_set_importance(port, value);
+		res = tipc_port_set_importance(port, value);
 		break;
 	case TIPC_SRC_DROPPABLE:
 		if (sock->type != SOCK_STREAM)