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* [PATCH] Fix an OOB access bug in technisat_usb2_get_ir
@ 2019-08-20 18:19 Hui Peng
  2019-08-20 18:24 ` Hui Peng
  2019-08-21 10:44 ` Sean Young
  0 siblings, 2 replies; 3+ messages in thread
From: Hui Peng @ 2019-08-20 18:19 UTC (permalink / raw)
  To: security
  Cc: Hui Peng, Mathias Payer, Mauro Carvalho Chehab, Hans Verkuil,
	Kees Cook, linux-media, linux-kernel

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@gmail.com>
Reported-by: Mathias Payer <mathias.payer@nebelwelt.net>
Signed-off-by: Hui Peng <benquike@gmail.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


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2019-08-20 18:19 [PATCH] Fix an OOB access bug in technisat_usb2_get_ir Hui Peng
2019-08-20 18:24 ` Hui Peng
2019-08-21 10:44 ` Sean Young

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