linux-kernel - Re: [PATCH] media: technisat-usb2: break out of loop at end of buffer

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Date:   Wed, 3 Jul 2019 09:54:53 -0700
From:   Kees Cook <keescook@...omium.org>
To:     Sean Young <sean@...s.org>
Cc:     syzbot <syzbot+eaaaf38a95427be88f4b@...kaller.appspotmail.com>,
        andreyknvl@...gle.com, hans.verkuil@...co.com,
        linux-kernel@...r.kernel.org, linux-media@...r.kernel.org,
        linux-usb@...r.kernel.org, mchehab@...nel.org,
        syzkaller-bugs@...glegroups.com,
        Phong Tran <tranmanphong@...il.com>
Subject: Re: [PATCH] media: technisat-usb2: break out of loop at end of buffer

On Wed, Jul 03, 2019 at 03:52:39PM +0100, Sean Young wrote:
> Ensure we do not access the buffer beyond the end if no 0xff byte
> is encountered.
> 
> Reported-by: syzbot+eaaaf38a95427be88f4b@...kaller.appspotmail.com
> Signed-off-by: Sean Young <sean@...s.org>

Both you and Phong Tran appear to be working on fixing this. At a
glance, this patch appears to be more complete in that it makes the code
flow more sane too.

Reviewed-by: Kees Cook <keescook@...omium.org>

-Kees

> ---
>  drivers/media/usb/dvb-usb/technisat-usb2.c | 22 ++++++++++------------
>  1 file changed, 10 insertions(+), 12 deletions(-)
> 
> diff --git a/drivers/media/usb/dvb-usb/technisat-usb2.c b/drivers/media/usb/dvb-usb/technisat-usb2.c
> index c659e18b358b..676d233d46d5 100644
> --- a/drivers/media/usb/dvb-usb/technisat-usb2.c
> +++ b/drivers/media/usb/dvb-usb/technisat-usb2.c
> @@ -608,10 +608,9 @@ static int technisat_usb2_frontend_attach(struct dvb_usb_adapter *a)
>  static int technisat_usb2_get_ir(struct dvb_usb_device *d)
>  {
>  	struct technisat_usb2_state *state = d->priv;
> -	u8 *buf = state->buf;
> -	u8 *b;
> -	int ret;
>  	struct ir_raw_event ev;
> +	u8 *buf = state->buf;
> +	int i, ret;
>  
>  	buf[0] = GET_IR_DATA_VENDOR_REQUEST;
>  	buf[1] = 0x08;
> @@ -647,26 +646,25 @@ static int technisat_usb2_get_ir(struct dvb_usb_device *d)
>  		return 0; /* no key pressed */
>  
>  	/* decoding */
> -	b = buf+1;
>  
>  #if 0
>  	deb_rc("RC: %d ", ret);
> -	debug_dump(b, ret, deb_rc);
> +	debug_dump(buf + 1, ret, deb_rc);
>  #endif
>  
>  	ev.pulse = 0;
> -	while (1) {
> -		ev.pulse = !ev.pulse;
> -		ev.duration = (*b * FIRMWARE_CLOCK_DIVISOR * FIRMWARE_CLOCK_TICK) / 1000;
> -		ir_raw_event_store(d->rc_dev, &ev);
> -
> -		b++;
> -		if (*b == 0xff) {
> +	for (i = 1; i < ARRAY_SIZE(state->buf); i++) {
> +		if (buf[i] == 0xff) {
>  			ev.pulse = 0;
>  			ev.duration = 888888*2;
>  			ir_raw_event_store(d->rc_dev, &ev);
>  			break;
>  		}
> +
> +		ev.pulse = !ev.pulse;
> +		ev.duration = (buf[i] * FIRMWARE_CLOCK_DIVISOR *
> +			       FIRMWARE_CLOCK_TICK) / 1000;
> +		ir_raw_event_store(d->rc_dev, &ev);
>  	}
>  
>  	ir_raw_event_handle(d->rc_dev);
> -- 
> 2.21.0
> 

-- 
Kees Cook