mISDN: fix use-after-free bugs in l1oip timer handlers

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 add a bool flag to show
if card is released. Then, check this flag in hc->workq
and hc->socket_thread.

Fixes: 3712b42d4b1b ("Add layer1 over IP support")
Signed-off-by: Duoming Zhou <duoming@zju.edu.cn>
Reviewed-by: Leon Romanovsky <leonro@nvidia.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

1 files changed, 1 insertions, 0 deletions

diff --git a/drivers/isdn/mISDN/l1oip.h b/drivers/isdn/mISDN/l1oip.h
index 7ea10db20e3a..48133d022812 100644
--- a/drivers/isdn/mISDN/l1oip.h
+++ b/drivers/isdn/mISDN/l1oip.h
@@ -59,6 +59,7 @@ struct l1oip {
 	int			bundle;		/* bundle channels in one frm */
 	int			codec;		/* codec to use for transmis. */
 	int			limit;		/* limit number of bchannels */
+	bool			shutdown;	/* if card is released */
 
 	/* timer */
 	struct timer_list	keep_tl;