char: tlclk: fix use-after-free in tlclk_cleanup()

[ Upstream commit bbf003b779 ]

This patch improves the module cleanup process in the tlclk driver to
prevent potential use-after-free and race conditions.

Currently, the file_operations structure does not specify the .owner
field, which could allow the module to be unloaded while user-space
processes are still interacting with the device. Additionally, the
tlclk_cleanup() function frees the alarm_events memory before ensuring
that blocked processes in the waitqueue are fully awakened and that the
switchover_timer has completed.

To address these cases, this patch:
- Sets '.owner = THIS_MODULE' in tlclk_fops to safely defer module
  unloading while the device is in use.
- Updates tlclk_cleanup() to explicitly wake up all blocked readers
  (wake_up_all), properly release hardware I/O regions, and safely
  delete the timer (timer_delete_sync) prior to freeing memory.

Fixes: 1a80ba8827 ("[PATCH] Telecom Clock Driver for MPCBL0010 ATCA computer blade")
Signed-off-by: James Kim <james010kim@gmail.com>
Link: https://patch.msgid.link/20260503101131.64219-1-james010kim@gmail.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Sasha Levin <sashal@kernel.org>

drivers/char/tlclk.c

@@ -263,6 +263,7 @@ static ssize_t tlclk_read(struct file *filp, char __user *buf, size_t count,
 }
 
 static const struct file_operations tlclk_fops = {
+	.owner = THIS_MODULE,
 	.read = tlclk_read,
 	.open = tlclk_open,
 	.release = tlclk_release,
@@ -852,6 +853,9 @@ static void __exit tlclk_cleanup(void)
 	misc_deregister(&tlclk_miscdev);
 	unregister_chrdev(tlclk_major, "telco_clock");
 
+	got_event = 1;
+	wake_up_all(&wq);
+
 	release_region(TLCLK_BASE, 8);
 	del_timer_sync(&switchover_timer);
 	kfree(alarm_events);