[PATCH v2] media: ttusb-dec: fix heap-buffer-overflow in ttusb_dec_process_urb_frame()

[pip-izony <eeodqql09@gmail.com>]

From: Seungjin Bae <eeodqql09@gmail.com>

The `ttusb_dec_process_urb_frame()` parses the PVA packet from the
USB device. However, it doesn't check whether the calculated
`packet_payload_length` exceeds the size of the `packet` buffer.

The `packet` buffer has a fixed size of `MAX_PVA_LENGTH + 4`. However,
`packet_payload_length` is derived from 2 bytes of the input data,
allowing a maximum value of 65543 bytes (8 + 0xFFFF).

If a malicious USB device sends a packet with crafted data, it
triggers a heap buffer overflow. This allows an attacker to overwrite
adjacent fields in the `struct ttusb_dec`. Specifically, the `a_pes2ts`
field, which contains a callback function pointer, is located after the
`packet` buffer. Overwriting this pointer can lead to control flow
hijacking.

Fix this by adding a bounds check for the parsed length against the
buffer size.

Fixes: 1da177e4c3f4 ("Linux-2.6.12-rc2")
Co-developed-by: Sanghoon Choi <csh0052@gmail.com>
Signed-off-by: Sanghoon Choi <csh0052@gmail.com>
Signed-off-by: Seungjin Bae <eeodqql09@gmail.com>
---
 v1 -> v2: Change warning function
 
 drivers/media/usb/ttusb-dec/ttusb_dec.c | 13 +++++++++++--
 1 file changed, 11 insertions(+), 2 deletions(-)

diff --git a/drivers/media/usb/ttusb-dec/ttusb_dec.c b/drivers/media/usb/ttusb-dec/ttusb_dec.c
index b4575fe89c95..0e983783e787 100644
--- a/drivers/media/usb/ttusb-dec/ttusb_dec.c
+++ b/drivers/media/usb/ttusb-dec/ttusb_dec.c
@@ -703,10 +703,19 @@ static void ttusb_dec_process_urb_frame(struct ttusb_dec *dec, u8 *b,
 
 			if (dec->packet_type == TTUSB_DEC_PACKET_PVA &&
 			    dec->packet_length == 8) {
-				dec->packet_state++;
-				dec->packet_payload_length = 8 +
+				int len = 8 +
 					(dec->packet[6] << 8) +
 					dec->packet[7];
+
+				if (len > MAX_PVA_LENGTH + 4) {
+					dev_warn(&dec->udev->dev,
+						"%s: packet too long - discarding\n"
+						__func__);
+					dec->packet_state = 0;
+				} else {
+					dec->packet_state++;
+					dec->packet_payload_length = len;
+				}
 			} else if (dec->packet_type ==
 					TTUSB_DEC_PACKET_SECTION &&
 				   dec->packet_length == 5) {
-- 
2.43.0