[PATCH] usb: storage: realtek_cr: fix use-after-free on disconnect

[Myeonghun Pak <mhun512@gmail.com>]

realtek_cr_destructor() calls timer_delete() before the chip containing
the timer is freed. The timer callback may still be running and can
rearm itself, resulting in a use-after-free.

Use timer_shutdown_sync() to wait for the callback and prevent further
rearming. Do this unconditionally because ss_en may be changed after
the timer is armed.

Move timer_setup() into init_realtek_cr() so the timer is initialized
before any failure path can invoke the destructor.

Found by static analysis.

Fixes: e931830bb877 ("Realtek cr: Add autosuspend function.")
Cc: stable@vger.kernel.org
Co-developed-by: Ijae Kim <ae878000@gmail.com>
Signed-off-by: Ijae Kim <ae878000@gmail.com>
Signed-off-by: Myeonghun Pak <mhun512@gmail.com>
---
 drivers/usb/storage/realtek_cr.c | 9 ++++-----
 1 file changed, 4 insertions(+), 5 deletions(-)

diff --git a/drivers/usb/storage/realtek_cr.c b/drivers/usb/storage/realtek_cr.c
index af038b897c6b..c4b28744693b 100644
--- a/drivers/usb/storage/realtek_cr.c
+++ b/drivers/usb/storage/realtek_cr.c
@@ -916,7 +916,6 @@ static int realtek_cr_autosuspend_setup(struct us_data *us)
 	us->proto_handler = rts51x_invoke_transport;
 
 	chip->timer_expires = 0;
-	timer_setup(&chip->rts51x_suspend_timer, rts51x_suspend_timer_fn, 0);
 	fw5895_init(us);
 
 	/* enable autosuspend function of the usb device */
@@ -934,10 +933,7 @@ static void realtek_cr_destructor(void *extra)
 		return;
 
 #ifdef CONFIG_REALTEK_AUTOPM
-	if (ss_en) {
-		timer_delete(&chip->rts51x_suspend_timer);
-		chip->timer_expires = 0;
-	}
+	timer_shutdown_sync(&chip->rts51x_suspend_timer);
 #endif
 	kfree(chip->status);
 }
@@ -982,6 +978,9 @@ static int init_realtek_cr(struct us_data *us)
 
 	us->extra = chip;
 	us->extra_destructor = realtek_cr_destructor;
+#ifdef CONFIG_REALTEK_AUTOPM
+	timer_setup(&chip->rts51x_suspend_timer, rts51x_suspend_timer_fn, 0);
+#endif
 	us->max_lun = chip->max_lun = rts51x_get_max_lun(us);
 	chip->us = us;
 
-- 
2.47.1