IPC: bugfix for msgrcv with msgtyp < 0

According to 'man msgrcv': "If msgtyp is less than 0, the first message of
the lowest type that is less than or equal to the absolute value of msgtyp
shall be received."

Bug: The kernel only returns a message if its type is 1; other messages
with type < abs(msgtype) will never get returned.

Fix: After having traversed the list to find the first message with the
lowest type, we need to actually return that message.

This regression was introduced by commit daaf74c ("ipc: refactor
msg list search into separate function")

Signed-off-by: Svenning Soerensen <[email protected]>
Reviewed-by: Peter Hurley <[email protected]>
Cc: <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>
Signed-off-by: Linus Torvalds <[email protected]>

Author: Svenning Sørensen

ipc/msg.c

@@ -839,7 +839,7 @@ static inline void free_copy(struct msg_msg *copy)
 
 static struct msg_msg *find_msg(struct msg_queue *msq, long *msgtyp, int mode)
 {
-	struct msg_msg *msg;
+	struct msg_msg *msg, *found = NULL;
 	long count = 0;
 
 	list_for_each_entry(msg, &msq->q_messages, m_list) {
@@ -848,6 +848,7 @@ static struct msg_msg *find_msg(struct msg_queue *msq, long *msgtyp, int mode)
 					       *msgtyp, mode)) {
 			if (mode == SEARCH_LESSEQUAL && msg->m_type != 1) {
 				*msgtyp = msg->m_type - 1;
+				found = msg;
 			} else if (mode == SEARCH_NUMBER) {
 				if (*msgtyp == count)
 					return msg;
@@ -857,7 +858,7 @@ static struct msg_msg *find_msg(struct msg_queue *msq, long *msgtyp, int mode)
 		}
 	}
 
-	return ERR_PTR(-EAGAIN);
+	return found ?: ERR_PTR(-EAGAIN);
 }
 
 long do_msgrcv(int msqid, void __user *buf, size_t bufsz, long msgtyp, int msgflg,