ACK: [PATCH 1/1] mISDN: fix use-after-free bugs in l1oip timer handlers

[Tim Gardner]

On 1/24/23 8:23 AM, Yuxuan Luo wrote:
> From: Duoming Zhou <duoming at zju.edu.cn>
> 
> 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 at zju.edu.cn>
> Reviewed-by: Leon Romanovsky <leonro at nvidia.com>
> Signed-off-by: David S. Miller <davem at davemloft.net>
> (cherry picked from commit 2568a7e0832ee30b0a351016d03062ab4e0e0a3f)
> CVE-2022-3565
> Signed-off-by: Yuxuan Luo <yuxuan.luo at canonical.com>
> ---
>   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 7ea10db20e3a6..48133d0228120 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 2c40412466e6f..a77195e378b7b 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);
>   
Acked-by: Tim Gardner <tim.gardner at canonical.com>
-- 
-----------
Tim Gardner
Canonical, Inc