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 daaf74cf0867 ("ipc: refactor
msg list search into separate function")

Signed-off-by: Svenning Soerensen <sss@secomea.dk>
Reviewed-by: Peter Hurley <peter@hurleysoftware.com>
Cc: <stable@vger.kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 3 insertions, 2 deletions

diff --git a/ipc/msg.c b/ipc/msg.c
index bd60d7e159e8..9f29d9e89bac 100644
--- a/ipc/msg.c
+++ b/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,