[PATCH 1/2] ipmi: Fix use-after-free and list corruption on sender error

[Corey Minyard <corey@minyard.net>]

The analysis from Breno:

When the SMI sender returns an error, smi_work() delivers an error
response but then jumps back to restart without cleaning up properly:

1. intf->curr_msg is not cleared, so no new message is pulled
2. newmsg still points to the message, causing sender() to be called
   again with the same message
3. If sender() fails again, deliver_err_response() is called with
   the same recv_msg that was already queued for delivery

This causes list_add corruption ("list_add double add") because the
recv_msg is added to the user_msgs list twice. Subsequently, the
corrupted list leads to use-after-free when the memory is freed and
reused, and eventually a NULL pointer dereference when accessing
recv_msg->done.

The buggy sequence:

  sender() fails
    -> deliver_err_response(recv_msg)  // recv_msg queued for delivery
    -> goto restart                    // curr_msg not cleared!
  sender() fails again (same message!)
    -> deliver_err_response(recv_msg)  // tries to queue same recv_msg
    -> LIST CORRUPTION

Fix this by freeing the message and setting it to NULL on a send error.
Also, always free the newmsg on a send error, otherwise it will leak.

Reported-by: Breno Leitao <leitao@debian.org>
Fixes: 9cf93a8fa9513 ("ipmi: Allow an SMI sender to return an error")
Signed-off-by: Corey Minyard <corey@minyard.net>
---
 drivers/char/ipmi/ipmi_msghandler.c | 11 +++++++++--
 1 file changed, 9 insertions(+), 2 deletions(-)

diff --git a/drivers/char/ipmi/ipmi_msghandler.c b/drivers/char/ipmi/ipmi_msghandler.c
index 3f48fc6ab596..a590a67294e2 100644
--- a/drivers/char/ipmi/ipmi_msghandler.c
+++ b/drivers/char/ipmi/ipmi_msghandler.c
@@ -4852,8 +4852,15 @@ static void smi_work(struct work_struct *t)
 			if (newmsg->recv_msg)
 				deliver_err_response(intf,
 						     newmsg->recv_msg, cc);
-			else
-				ipmi_free_smi_msg(newmsg);
+			if (!run_to_completion)
+				spin_lock_irqsave(&intf->xmit_msgs_lock,
+						  flags);
+			intf->curr_msg = NULL;
+			if (!run_to_completion)
+				spin_unlock_irqrestore(&intf->xmit_msgs_lock,
+						       flags);
+			ipmi_free_smi_msg(newmsg);
+			newmsg = NULL;
 			goto restart;
 		}
 	}
-- 
2.43.0