[PATCH 5.10 080/145] USB: cdc-wdm: Fix use after free in service_outstanding_interrupt().

Greg Kroah-Hartman
2021-01-11T13:27:07Z

From: Tetsuo Handa <penguin-kernel@i-love.sakura.ne.jp>

commit 5e5ff0b4b6bcb4d17b7a26ec8bcfc7dd4651684f upstream.

syzbot is reporting UAF at usb_submit_urb() [1], for
service_outstanding_interrupt() is not checking WDM_DISCONNECTING
before calling usb_submit_urb(). Close the race by doing same checks
wdm_read() does upon retry.

Also, while wdm_read() checks WDM_DISCONNECTING with desc->rlock held,
service_interrupt_work() does not hold desc->rlock. Thus, it is possible
that usb_submit_urb() is called from service_outstanding_interrupt() from
service_interrupt_work() after WDM_DISCONNECTING was set and kill_urbs()
from wdm_disconnect() completed. Thus, move kill_urbs() in
wdm_disconnect() to after cancel_work_sync() (which makes sure that
service_interrupt_work() is no longer running) completed.

Although it seems to be safe to dereference desc->intf->dev in
service_outstanding_interrupt() even if WDM_DISCONNECTING was already set
because desc->rlock or cancel_work_sync() prevents wdm_disconnect() from
reaching list_del() before service_outstanding_interrupt() completes,
let's not emit error message if WDM_DISCONNECTING is set by
wdm_disconnect() while usb_submit_urb() is in progress.

[1] https://syzkaller.appspot.com/bug?extid=9e04e2df4a32fb661daf

Reported-by: syzbot <syzbot+9e04e2df4a32fb661daf@syzkaller.appspotmail.com>
Signed-off-by: Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp>
Cc: stable <stable@vger.kernel.org>
Link: https://lore.kernel.org/r/620e2ee0-b9a3-dbda-a25b-a93e0ed03ec5@i-love.sakura.ne.jp
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

---
drivers/usb/class/cdc-wdm.c | 16 +++++++++++++---
1 file changed, 13 insertions(+), 3 deletions(-)

--- a/drivers/usb/class/cdc-wdm.c
+++ b/drivers/usb/class/cdc-wdm.c
@@ -465,13 +465,23 @@ static int service_outstanding_interrupt
if (!desc->resp_count || !--desc->resp_count)
goto out;

+ if (test_bit(WDM_DISCONNECTING, &desc->flags)) {
+ rv = -ENODEV;
+ goto out;
+ }
+ if (test_bit(WDM_RESETTING, &desc->flags)) {
+ rv = -EIO;
+ goto out;
+ }
+
set_bit(WDM_RESPONDING, &desc->flags);
spin_unlock_irq(&desc->iuspin);
rv = usb_submit_urb(desc->response, GFP_KERNEL);
spin_lock_irq(&desc->iuspin);
if (rv) {
- dev_err(&desc->intf->dev,
- "usb_submit_urb failed with result %d\n", rv);
+ if (!test_bit(WDM_DISCONNECTING, &desc->flags))
+ dev_err(&desc->intf->dev,
+ "usb_submit_urb failed with result %d\n", rv);

/* make sure the next notification trigger a submit */
clear_bit(WDM_RESPONDING, &desc->flags);
@@ -1027,9 +1037,9 @@ static void wdm_disconnect(struct usb_in
wake_up_all(&desc->wait);
mutex_lock(&desc->rlock);
mutex_lock(&desc->wlock);
- kill_urbs(desc);
cancel_work_sync(&desc->rxwork);
cancel_work_sync(&desc->service_outs_intr);
+ kill_urbs(desc);
mutex_unlock(&desc->wlock);
mutex_unlock(&desc->rlock);