[PATCH v2 5/5] can: peak_usb: harden PCAN-USB message validation

[Stéphane Grosjean]

From: Stéphane Grosjean <s.grosjean@xxxxxxxxxxxxxx>

Add boundary checks when parsing PCAN-USB messages and reject
malformed buffers whose contents would otherwise lead to accesses
outside the received USB data area.

This prevents potential out-of-bounds memory accesses caused by
corrupted or malicious device messages.

Fixes: 46be265d3388 ("can: usb: PEAK-System Technik PCAN-USB specific part")
Signed-off-by: Stéphane Grosjean <s.grosjean@xxxxxxxxxxxxxx>
---
 drivers/net/can/usb/peak_usb/pcan_usb.c | 24 ++++++++++++++++--------
 1 file changed, 16 insertions(+), 8 deletions(-)

diff --git a/drivers/net/can/usb/peak_usb/pcan_usb.c b/drivers/net/can/usb/peak_usb/pcan_usb.c
index 169c00d93463..56ddd134bae0 100644
--- a/drivers/net/can/usb/peak_usb/pcan_usb.c
+++ b/drivers/net/can/usb/peak_usb/pcan_usb.c
@@ -696,8 +696,11 @@ static int pcan_usb_decode_data(struct pcan_usb_msg_context *mc, u8 status_len)
 		mc->ptr += rec_len;
 
 		/* Ignore next byte (client private id) if SRR bit is set */
-		if (can_id_flags & PCAN_USB_TX_SRR)
+		if (can_id_flags & PCAN_USB_TX_SRR) {
+			if ((mc->ptr + 1) > mc->end)
+				goto decode_failed;
 			mc->ptr++;
+		}
 
 		/* update statistics */
 		mc->netdev->stats.rx_bytes += cf->len;
@@ -733,14 +736,19 @@ static int pcan_usb_decode_msg(struct peak_usb_device *dev, u8 *ibuf, u32 lbuf)
 	int err;
 
 	for (err = 0; mc.rec_idx < mc.rec_cnt && !err; mc.rec_idx++) {
-		u8 sl = *mc.ptr++;
-
-		/* handle status and error frames here */
-		if (sl & PCAN_USB_STATUSLEN_INTERNAL) {
-			err = pcan_usb_decode_status(&mc, sl);
-		/* handle normal can frames here */
+		/* check if status_len byte can be read next */
+		if (mc.ptr >= mc.end) {
+			err = -EINVAL;
 		} else {
-			err = pcan_usb_decode_data(&mc, sl);
+			u8 sl = *mc.ptr++;
+
+			/* handle status and error frames here */
+			if (sl & PCAN_USB_STATUSLEN_INTERNAL) {
+				err = pcan_usb_decode_status(&mc, sl);
+			/* handle normal can frames here */
+			} else {
+				err = pcan_usb_decode_data(&mc, sl);
+			}
 		}
 	}
 

-- 
2.43.0