[PATCH] ipmi: Fix handling of messages with provided receive message pointer

[Guenter Roeck <linux@roeck-us.net>]

Prior to commit b52da4054ee0 ("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: b52da4054ee0 ("ipmi: Rework user message limit handling")
Reported-by: Eric Dumazet <edumazet@google.com>
Cc: Eric Dumazet <edumazet@google.com>
Cc: Greg Thelen <gthelen@google.com>
Signed-off-by: Guenter Roeck <linux@roeck-us.net>
---
 drivers/char/ipmi/ipmi_msghandler.c | 5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)

diff --git a/drivers/char/ipmi/ipmi_msghandler.c b/drivers/char/ipmi/ipmi_msghandler.c
index a0b67a35a5f0..3700ab4eba3e 100644
--- a/drivers/char/ipmi/ipmi_msghandler.c
+++ b/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))
-- 
2.45.2