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IPC: bugfix for msgrcv with msgtyp < 0

PATCH In review Svenning Sørensen 3 participants 5 messages Aug 24, 2013 – Aug 26, 2013

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Svenning Sørensen

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#0 lore raw

PATCH 1/1 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.

Signed-off-by Svenning Soerensen <[email protected]>
ipc/msg.c +3 -2
index bd60d7e..9f29d9e 100644
@@ -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,
Reviewed-by on v1 1/1
#1 lore raw
Quoted 9 lines · Svenning Sørensen

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.

Sorry for the breakage. Needs to go to -stable as well.

Reviewed-by Peter Hurley <[email protected]>
#2 lore raw
Quoted 5 lines · On Sat, 24 Aug 2013 08:49:25 -0400 Peter Hurley <[email protected]>…
Quoted 4 lines · Svenning S__rensen

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."

Quoted 7 lines
Quoted 5 lines

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.

Sorry for the breakage. Needs to go to -stable as well.

Do you know which commit caused the regression? That would help those who wish to fix up their kernels.

Quoted 2 lines
Reviewed-by Peter Hurley <[email protected]>
#3 lore raw
Quoted 10 lines · Andrew Morton
Quoted 8 lines · On Sat, 24 Aug 2013 08:49:25 -0400 Peter Hurley <[email protected]>…
Quoted 7 lines · Svenning S__rensen

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.

Quoted 7 lines
Quoted 4 lines
Quoted 2 lines

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

Sorry for the breakage. Needs to go to -stable as well.

Do you know which commit caused the regression? That would help those who wish to fix up their kernels.

Commit daaf74cf0867e3042090d56d10b194d6265b4684,
ipc: refactor msg list search into separate function introduced this regression.

Regards,
Peter Hurley

Quoted 2 lines
Quoted 2 lines
Reviewed-by Peter Hurley <[email protected]>
#4 lore raw
In reply to Svenning Sørensen
Quoted 26 lines · On Sat, 24 Aug 2013 13:44:49 +0200 Svenning S__rensen <[email protected]> wrote:

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.

Signed-off-by Svenning Soerensen <[email protected]>
ipc/msg.c +1 -1
index bd60d7e..9f29d9e 100644
@@ -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) {

ipc/msg.c static struct msg_msg *find_msg(struct msg_queue *msq, long *msgtyp, int mode) · line 851

Quoted 4 lines
ipc/msg.c +1 -0
@@ -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;

Should we continue the search in this case, or should the code immediately return this message?

Quoted 12 lines
ipc/msg.c +1 -1
  			} 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,