ipmi: Fix handling of messages with provided receive message pointer

Prior to commit b52da40 ("ipmi: Rework user message limit handling"),
i_ipmi_request() used to increase the user reference counter if the receive
message is provided by the caller of IPMI API functions. This is no longer
the case. However, ipmi_free_recv_msg() is still called and decreases the
reference counter. This results in the reference counter reaching zero,
the user data pointer is released, and all kinds of interesting crashes are
seen.

Fix the problem by increasing user reference counter if the receive message
has been provided by the caller.

Fixes: b52da40 ("ipmi: Rework user message limit handling")
Reported-by: Eric Dumazet <[email protected]>
Cc: Eric Dumazet <[email protected]>
Cc: Greg Thelen <[email protected]>
Signed-off-by: Guenter Roeck <[email protected]>
Message-ID: <[email protected]>
Signed-off-by: Corey Minyard <[email protected]>

Author: groeck

drivers/char/ipmi/ipmi_msghandler.c

@@ -2301,8 +2301,11 @@ static int i_ipmi_request(struct ipmi_user     *user,
 	if (supplied_recv) {
 		recv_msg = supplied_recv;
 		recv_msg->user = user;
-		if (user)
+		if (user) {
 			atomic_inc(&user->nr_msgs);
+			/* The put happens when the message is freed. */
+			kref_get(&user->refcount);
+		}
 	} else {
 		recv_msg = ipmi_alloc_recv_msg(user);
 		if (IS_ERR(recv_msg))