ipmi: fix use after free in _ipmi_destroy_user()

commit a92ce57 upstream.

The intf_free() function frees the "intf" pointer so we cannot
dereference it again on the next line.

Fixes: cbb7986 ("ipmi: Don't allow device module unload when in use")
Signed-off-by: Dan Carpenter <error27@gmail.com>
Message-Id: <Y3M8xa1drZv4CToE@kili>
Cc: <stable@vger.kernel.org> # 5.5+
Signed-off-by: Corey Minyard <cminyard@mvista.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/char/ipmi/ipmi_msghandler.c

@@ -1273,6 +1273,7 @@ static void _ipmi_destroy_user(struct ipmi_user *user)
 	unsigned long    flags;
 	struct cmd_rcvr  *rcvr;
 	struct cmd_rcvr  *rcvrs = NULL;
+	struct module    *owner;
 
 	if (!acquire_ipmi_user(user, &i)) {
 		/*
@@ -1334,8 +1335,9 @@ static void _ipmi_destroy_user(struct ipmi_user *user)
 		kfree(rcvr);
 	}
 
+	owner = intf->owner;
 	kref_put(&intf->refcount, intf_free);
-	module_put(intf->owner);
+	module_put(owner);
 }
 
 int ipmi_destroy_user(struct ipmi_user *user)