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 <[email protected]>
---
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);
if (hc->socket_thread)
l1oip_socket_close(hc);
+ del_timer_sync(&hc->timeout_tl);
+
if (hc->registered && hc->chan[hc->d_idx].dch)
mISDN_unregister_device(&hc->chan[hc->d_idx].dch->dev);
for (ch = 0; ch < 128; ch++) {
--
2.17.1
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 <[email protected]>
> ---
> 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."
Thanks
>
> if (hc->socket_thread)
> l1oip_socket_close(hc);
>
> + del_timer_sync(&hc->timeout_tl);
> +
> if (hc->registered && hc->chan[hc->d_idx].dch)
> mISDN_unregister_device(&hc->chan[hc->d_idx].dch->dev);
> for (ch = 0; ch < 128; ch++) {
> --
> 2.17.1
>
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 <[email protected]>
> > ---
> > 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