[PATCH] ipmi: Fix user refcount underflow in event delivery

[Matt Fleming <matt@readmodwrite.com>]

From: Matt Fleming <mfleming@cloudflare.com>

ipmi_alloc_recv_msg(user) takes the temporary user reference owned by the
receive message, and ipmi_free_recv_msg() drops it again. If event delivery
fails after allocating receive messages for earlier users,
handle_read_event_rsp() rolls those messages back with
ipmi_free_recv_msg().

That rollback path still drops user->refcount explicitly after freeing each
message. The extra put can free a user that remains linked on intf->users,
so later event delivery may dereference a freed user or trip refcount_t's
addition-on-zero warning when ipmi_alloc_recv_msg() tries to acquire
another reference.

Remove the stale explicit put and the now-dead user assignment. Keep the
list_del() and ipmi_free_recv_msg() calls; they are the required rollback
operations.

Fixes: b52da4054ee0 ("ipmi: Rework user message limit handling")
Cc: stable@vger.kernel.org
Signed-off-by: Matt Fleming <mfleming@cloudflare.com>
---
 drivers/char/ipmi/ipmi_msghandler.c | 2 --
 1 file changed, 2 deletions(-)

diff --git a/drivers/char/ipmi/ipmi_msghandler.c b/drivers/char/ipmi/ipmi_msghandler.c
index 869ac87a4b6a..52561a880e54 100644
--- a/drivers/char/ipmi/ipmi_msghandler.c
+++ b/drivers/char/ipmi/ipmi_msghandler.c
@@ -4477,10 +4477,8 @@ static int handle_read_event_rsp(struct ipmi_smi *intf,
 			mutex_unlock(&intf->users_mutex);
 			list_for_each_entry_safe(recv_msg, recv_msg2, &msgs,
 						 link) {
-				user = recv_msg->user;
 				list_del(&recv_msg->link);
 				ipmi_free_recv_msg(recv_msg);
-				kref_put(&user->refcount, free_ipmi_user);
 			}
 			/*
 			 * We couldn't allocate memory for the
-- 
2.43.0