IPC: bugfix for msgrcv with msgtyp < 0

commit 368ae537 upstream.

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 daaf74cf ("ipc: refactor
msg list search into separate function")
Signed-off-by: Svenning Soerensen <sss@secomea.dk>
Reviewed-by: Peter Hurley <peter@hurleysoftware.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

ipc/msg.c

@@ -795,7 +795,7 @@ 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) {
@@ -804,6 +804,7 @@ 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;
@@ -813,7 +814,7 @@ static struct msg_msg *find_msg(struct msg_queue *msq, long *msgtyp, int mode)
 		}
 	}
 
-	return ERR_PTR(-EAGAIN);
+	return found ?: ERR_PTR(-EAGAIN);
 }