Re: [PATCH] Fix an OOB access bug in technisat_usb2_get_ir

[Hui Peng]

The following is the kasan report. This bug was found in v4.20-rc2, but
it is present in the latest version.

BUG: KASAN: slab-out-of-bounds in technisat_usb2_get_ir
drivers/media/usb/dvb-usb/technisat-usb2.c:664 [inline]
BUG: KASAN: slab-out-of-bounds in technisat_usb2_rc_query+0x598/0x5f0
drivers/media/usb/dvb-usb/technisat-usb2.c:679
Read of size 1 at addr ffff88805ee3d3a8 by task kworker/2:3/8681

CPU: 2 PID: 8681 Comm: kworker/2:3 Not tainted 4.20.0-rc2 #1
Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS
Ubuntu-1.8.2-1ubuntu1 04/01/2014
Workqueue: events dvb_usb_read_remote_control
Call Trace:
Â__dump_stack lib/dump_stack.c:77 [inline]
Âdump_stack+0xd2/0x148 lib/dump_stack.c:113
Âprint_address_description+0x71/0x239 mm/kasan/report.c:256
Âkasan_report_error mm/kasan/report.c:354 [inline]
Âkasan_report.cold.5+0x242/0x30b mm/kasan/report.c:412
Â__asan_report_load1_noabort+0x19/0x20 mm/kasan/report.c:430
Âtechnisat_usb2_get_ir drivers/media/usb/dvb-usb/technisat-usb2.c:664
[inline]
Âtechnisat_usb2_rc_query+0x598/0x5f0
drivers/media/usb/dvb-usb/technisat-usb2.c:679
Âdvb_usb_read_remote_control+0xbd/0x150
drivers/media/usb/dvb-usb/dvb-usb-remote.c:261
Âprocess_one_work+0x816/0x14d0 kernel/workqueue.c:2153
Âworker_thread+0x9b/0xce0 kernel/workqueue.c:2296
Âkthread+0x33d/0x400 kernel/kthread.c:246
Âret_from_fork+0x3a/0x50 arch/x86/entry/entry_64.S:352

On 8/20/19 2:19 PM, 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.
>
> Reported-by: Hui Peng <benquike@xxxxxxxxx>
> Reported-by: Mathias Payer <mathias.payer@xxxxxxxxxxxxx>
> Signed-off-by: Hui Peng <benquike@xxxxxxxxx>
> ---
>  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;