[PATCH 5.19 279/717] mISDN: fix use-after-free bugs in l1oip timer handlers

Greg Kroah-Hartman
2022-10-22T08:00:39Z

From: Duoming Zhou <duoming@zju.edu.cn>

[ Upstream commit 2568a7e0832ee30b0a351016d03062ab4e0e0a3f ]

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>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
drivers/isdn/mISDN/l1oip.h | 1 +
drivers/isdn/mISDN/l1oip_core.c | 13 +++++++------
2 files changed, 8 insertions(+), 6 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;
diff --git a/drivers/isdn/mISDN/l1oip_core.c b/drivers/isdn/mISDN/l1oip_core.c
index 2c40412466e6..a77195e378b7 100644
--- a/drivers/isdn/mISDN/l1oip_core.c
+++ b/drivers/isdn/mISDN/l1oip_core.c
@@ -275,7 +275,7 @@ l1oip_socket_send(struct l1oip *hc, u8 localcodec, u8 channel, u32 chanmask,
p = frame;

/* restart timer */
- if (time_before(hc->keep_tl.expires, jiffies + 5 * HZ))
+ if (time_before(hc->keep_tl.expires, jiffies + 5 * HZ) && !hc->shutdown)
mod_timer(&hc->keep_tl, jiffies + L1OIP_KEEPALIVE * HZ);
else
hc->keep_tl.expires = jiffies + L1OIP_KEEPALIVE * HZ;
@@ -601,7 +601,9 @@ l1oip_socket_parse(struct l1oip *hc, struct sockaddr_in *sin, u8 *buf, int len)
goto multiframe;

/* restart timer */
- if (time_before(hc->timeout_tl.expires, jiffies + 5 * HZ) || !hc->timeout_on) {
+ if ((time_before(hc->timeout_tl.expires, jiffies + 5 * HZ) ||
+ !hc->timeout_on) &&
+ !hc->shutdown) {
hc->timeout_on = 1;
mod_timer(&hc->timeout_tl, jiffies + L1OIP_TIMEOUT * HZ);
} else /* only adjust timer */
@@ -1232,11 +1234,10 @@ release_card(struct l1oip *hc)
{
int ch;

- if (timer_pending(&hc->keep_tl))
- del_timer(&hc->keep_tl);
+ hc->shutdown = true;

- 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);

--
2.35.1