Messages in this thread | | | Date | Wed, 28 Sep 2022 21:35:36 +0800 (GMT+08:00) | From | duoming@zju ... | Subject | Re: [PATCH V2] mISDN: fix use-after-free bugs in l1oip timer handlers |
| |
Hello,
On Wed, 28 Sep 2022 12:46:10 +0300 Leon Romanovsky wrote:
> On Fri, Sep 23, 2022 at 10:25:14PM +0800, Duoming Zhou wrote: > > 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->keep_tl) twice to stop keep_tl timer > > and hc->workq. Then, we add del_timer_sync(&hc->timeout_tl) > > behind l1oip_socket_close() to stop timeout_tl timer. > > > > Fixes: 3712b42d4b1b ("Add layer1 over IP support") > > Signed-off-by: Duoming Zhou <duoming@zju.edu.cn> > > --- > > Changes in v2: > > - Solve the problem that timers could be restarted by other threads. > > > > drivers/isdn/mISDN/l1oip_core.c | 11 +++++------ > > 1 file changed, 5 insertions(+), 6 deletions(-) > > > > diff --git a/drivers/isdn/mISDN/l1oip_core.c b/drivers/isdn/mISDN/l1oip_core.c > > index 2c40412466e..7b89d98a781 100644 > > --- a/drivers/isdn/mISDN/l1oip_core.c > > +++ b/drivers/isdn/mISDN/l1oip_core.c > > @@ -1232,17 +1232,16 @@ 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); > > + cancel_work_sync(&hc->workq); > > + del_timer_sync(&hc->keep_tl); > > cancel_work_sync(&hc->workq); > > It is racy, the call twice to del_timer_sync and cancel_work_sync > doesn't solve "the problem that timers could be restarted by other > threads."
Thank you for your reply! I will add a bool flag in struct l1oip to judge whether the card is released and check this flag in other threads.
Best regards, Duoming Zhou
| |