linux-kernel - Re: [PATCH] Fix an OOB access bug in technisat_usb2_get

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Date:   Wed, 21 Aug 2019 11:44:08 +0100
From:   Sean Young <sean@...s.org>
To:     Hui Peng <benquike@...il.com>
Cc:     security@...nel.org, Mathias Payer <mathias.payer@...elwelt.net>,
        Mauro Carvalho Chehab <mchehab@...nel.org>,
        Hans Verkuil <hans.verkuil@...co.com>,
        Kees Cook <keescook@...omium.org>, linux-media@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] Fix an OOB access bug in technisat_usb2_get_ir

On Tue, Aug 20, 2019 at 02:19:16PM -0400, Hui Peng wrote:
> In the while loop of technisat_usb2_get_ir, it scans through
> a fix-sized buffer read from the device side, the termination
> condition of the loop is `*b == 0xff`. If no `0xff` byte is read
> from the device side, OOB access happens.
> 
> This patch fixes the bug by adding an upper bound in the while loop.

This issue was fixed in:

 https://git.linuxtv.org/media_tree.git/commit/drivers/media/usb/dvb-usb/technisat-usb2.c?id=0c4df39e504bf925ab666132ac3c98d6cbbe380b

Note this limits the loop to the size of the buffer; using the ret
return value might be better.


Sean


> 
> Reported-by: Hui Peng <benquike@...il.com>
> Reported-by: Mathias Payer <mathias.payer@...elwelt.net>
> Signed-off-by: Hui Peng <benquike@...il.com>
> ---
>  drivers/media/usb/dvb-usb/technisat-usb2.c | 5 +++++
>  1 file changed, 5 insertions(+)
> 
> diff --git a/drivers/media/usb/dvb-usb/technisat-usb2.c b/drivers/media/usb/dvb-usb/technisat-usb2.c
> index c659e18b358b..181f5f97af45 100644
> --- a/drivers/media/usb/dvb-usb/technisat-usb2.c
> +++ b/drivers/media/usb/dvb-usb/technisat-usb2.c
> @@ -612,6 +612,7 @@ static int technisat_usb2_get_ir(struct dvb_usb_device *d)
>  	u8 *b;
>  	int ret;
>  	struct ir_raw_event ev;
> +	int i = 0;
>  
>  	buf[0] = GET_IR_DATA_VENDOR_REQUEST;
>  	buf[1] = 0x08;
> @@ -656,11 +657,15 @@ static int technisat_usb2_get_ir(struct dvb_usb_device *d)
>  
>  	ev.pulse = 0;
>  	while (1) {
> +		// only `ret` bytes are read from the device side
> +		if (i >= ret)
> +			break;
>  		ev.pulse = !ev.pulse;
>  		ev.duration = (*b * FIRMWARE_CLOCK_DIVISOR * FIRMWARE_CLOCK_TICK) / 1000;
>  		ir_raw_event_store(d->rc_dev, &ev);
>  
>  		b++;
> +		i++;
>  		if (*b == 0xff) {
>  			ev.pulse = 0;
>  			ev.duration = 888888*2;
> -- 
> 2.23.0