The l1oip_cleanup() traverses the l1oip_ilist and calls
release_card() to cleanup module and stack. However,
release_card() calls del_timer() to delete the timers
such as keep_tl and timeout_tl. If the timer handler is
running, the del_timer() will not stop it and result in
UAF bugs. One of the processes is shown below:
(cleanup routine) | (timer handler)
release_card() | l1oip_timeout()
... |
del_timer() | ...
... |
kfree(hc) //FREE |
| hc->timeout_on = 0 //USE
Fix by calling del_timer_sync() in release_card(), which
makes sure the timer handlers have finished before the
resources, such as l1oip and so on, have been deallocated.
What's more, the hc->workq and hc->socket_thread can kick
those timers right back in. We use del_timer_sync(&hc->keep_tl)
and cancel_work_sync(&hc->workq) twice to stop keep_tl timer
and hc->workq. Then, we add del_timer_sync(&hc->timeout_tl)
inside l1oip_socket_close() to stop timeout_tl timer. Because
the hc->socket_thread has been killed and the timeout_tl timer
will not be rescheduled.
Fixes: 3712b42d4b1b ("Add layer1 over IP support")
Signed-off-by: Duoming Zhou <[email protected]>
---
Changes in v3:
- Make commit messages more clearer.
- Add del_timer_sync(&hc->timeout_tl) inside l1oip_socket_close().
drivers/isdn/mISDN/l1oip_core.c | 12 ++++++------
1 file changed, 6 insertions(+), 6 deletions(-)
diff --git a/drivers/isdn/mISDN/l1oip_core.c b/drivers/isdn/mISDN/l1oip_core.c
index 2c40412466e..5939f1d8f08 100644
--- a/drivers/isdn/mISDN/l1oip_core.c
+++ b/drivers/isdn/mISDN/l1oip_core.c
@@ -762,6 +762,8 @@ l1oip_socket_close(struct l1oip *hc)
wait_for_completion(&hc->socket_complete);
}
+ del_timer_sync(&hc->timeout_tl);
+
/* if active, we send up a PH_DEACTIVATE and deactivate */
if (test_bit(FLG_ACTIVE, &dch->Flags)) {
if (debug & (DEBUG_L1OIP_MSG | DEBUG_L1OIP_SOCKET))
@@ -1232,12 +1234,10 @@ release_card(struct l1oip *hc)
{
int ch;
- if (timer_pending(&hc->keep_tl))
- del_timer(&hc->keep_tl);
-
- if (timer_pending(&hc->timeout_tl))
- del_timer(&hc->timeout_tl);
-
+ del_timer_sync(&hc->keep_tl);
+ del_timer_sync(&hc->timeout_tl);
+ cancel_work_sync(&hc->workq);
+ del_timer_sync(&hc->keep_tl);
cancel_work_sync(&hc->workq);
if (hc->socket_thread)
--
2.17.1
On Sat, 24 Sep 2022 10:18:42 +0800 Duoming Zhou wrote:
> + del_timer_sync(&hc->keep_tl);
> + del_timer_sync(&hc->timeout_tl);
> + cancel_work_sync(&hc->workq);
> + del_timer_sync(&hc->keep_tl);
> cancel_work_sync(&hc->workq);
Why not add a bit which will indicate that the device is shutting
down and check it in places which schedule the timer?
I think that's much easier to reason about and we won't need to do
this rep cancel procedure.
Hello,
On Tue, 27 Sep 2022 17:26:18 -0700 Jakub Kicinski wrote:
> On Sat, 24 Sep 2022 10:18:42 +0800 Duoming Zhou wrote:
> > + del_timer_sync(&hc->keep_tl);
> > + del_timer_sync(&hc->timeout_tl);
> > + cancel_work_sync(&hc->workq);
> > + del_timer_sync(&hc->keep_tl);
> > cancel_work_sync(&hc->workq);
>
> Why not add a bit which will indicate that the device is shutting
> down and check it in places which schedule the timer?
> I think that's much easier to reason about and we won't need to do
> this rep cancel procedure.
Thank you for your time and suggestions!
Best regards,
Duoming Zhou