Patch "ipmi: Remove smi_msg from waiting_rcv_msgs list before handle_one_recv_msg()" has been added to the 4.6-stable tree

[<gregkh@linuxfoundation.org>]

This is a note to let you know that I've just added the patch titled

    ipmi: Remove smi_msg from waiting_rcv_msgs list before handle_one_recv_msg()

to the 4.6-stable tree which can be found at:
    http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
     ipmi-remove-smi_msg-from-waiting_rcv_msgs-list-before-handle_one_recv_msg.patch
and it can be found in the queue-4.6 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@vger.kernel.org> know about it.


>From ae4ea9a2460c7fee2ae8feeb4dfe96f5f6c3e562 Mon Sep 17 00:00:00 2001
From: Junichi Nomura <j-nomura@ce.jp.nec.com>
Date: Fri, 10 Jun 2016 04:31:52 +0000
Subject: ipmi: Remove smi_msg from waiting_rcv_msgs list before handle_one_recv_msg()

From: Junichi Nomura <j-nomura@ce.jp.nec.com>

commit ae4ea9a2460c7fee2ae8feeb4dfe96f5f6c3e562 upstream.

Commit 7ea0ed2b5be8 ("ipmi: Make the message handler easier to use for
SMI interfaces") changed handle_new_recv_msgs() to call handle_one_recv_msg()
for a smi_msg while the smi_msg is still connected to waiting_rcv_msgs list.
That could lead to following list corruption problems:

1) low-level function treats smi_msg as not connected to list

  handle_one_recv_msg() could end up calling smi_send(), which
  assumes the msg is not connected to list.

  For example, the following sequence could corrupt list by
  doing list_add_tail() for the entry still connected to other list.

    handle_new_recv_msgs()
      msg = list_entry(waiting_rcv_msgs)
      handle_one_recv_msg(msg)
        handle_ipmb_get_msg_cmd(msg)
          smi_send(msg)
            spin_lock(xmit_msgs_lock)
            list_add_tail(msg)
            spin_unlock(xmit_msgs_lock)

2) race between multiple handle_new_recv_msgs() instances

  handle_new_recv_msgs() once releases waiting_rcv_msgs_lock before calling
  handle_one_recv_msg() then retakes the lock and list_del() it.

  If others call handle_new_recv_msgs() during the window shown below
  list_del() will be done twice for the same smi_msg.

  handle_new_recv_msgs()
    spin_lock(waiting_rcv_msgs_lock)
    msg = list_entry(waiting_rcv_msgs)
    spin_unlock(waiting_rcv_msgs_lock)
  |
  | handle_one_recv_msg(msg)
  |
    spin_lock(waiting_rcv_msgs_lock)
    list_del(msg)
    spin_unlock(waiting_rcv_msgs_lock)

Fixes: 7ea0ed2b5be8 ("ipmi: Make the message handler easier to use for SMI interfaces")
Signed-off-by: Jun'ichi Nomura <j-nomura@ce.jp.nec.com>
[Added a comment to describe why this works.]
Signed-off-by: Corey Minyard <cminyard@mvista.com>
Tested-by: Ye Feng <yefeng.yl@alibaba-inc.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

---
 drivers/char/ipmi/ipmi_msghandler.c |    8 ++++++--
 1 file changed, 6 insertions(+), 2 deletions(-)

--- a/drivers/char/ipmi/ipmi_msghandler.c
+++ b/drivers/char/ipmi/ipmi_msghandler.c
@@ -3820,6 +3820,7 @@ static void handle_new_recv_msgs(ipmi_sm
 	while (!list_empty(&intf->waiting_rcv_msgs)) {
 		smi_msg = list_entry(intf->waiting_rcv_msgs.next,
 				     struct ipmi_smi_msg, link);
+		list_del(&smi_msg->link);
 		if (!run_to_completion)
 			spin_unlock_irqrestore(&intf->waiting_rcv_msgs_lock,
 					       flags);
@@ -3829,11 +3830,14 @@ static void handle_new_recv_msgs(ipmi_sm
 		if (rv > 0) {
 			/*
 			 * To preserve message order, quit if we
-			 * can't handle a message.
+			 * can't handle a message.  Add the message
+			 * back at the head, this is safe because this
+			 * tasklet is the only thing that pulls the
+			 * messages.
 			 */
+			list_add(&smi_msg->link, &intf->waiting_rcv_msgs);
 			break;
 		} else {
-			list_del(&smi_msg->link);
 			if (rv == 0)
 				/* Message handled */
 				ipmi_free_smi_msg(smi_msg);


Patches currently in stable-queue which might be from j-nomura@ce.jp.nec.com are

queue-4.6/ipmi-remove-smi_msg-from-waiting_rcv_msgs-list-before-handle_one_recv_msg.patch