[PATCH 5.10] can: ems_usb: validate CPC message lengths

[PATCH 5.10] can: ems_usb: validate CPC message lengths

[Denis Arefev]

From: Pengpeng Hou <pengpeng@iscas.ac.cn>

commit 02925f51377f2a42a6724f00549167499c9302e5 upstream.

ems_usb_read_bulk_callback() walks CPC messages packed in one USB
receive buffer.

Check that each declared message fits in the URB payload. Also require the
type-specific payload to cover the fields used by the CAN, state, error and
overrun handlers.

Signed-off-by: Pengpeng Hou <pengpeng@iscas.ac.cn>
Link: https://patch.msgid.link/20260706092752.79600-1-pengpeng@iscas.ac.cn
Fixes: 702171adeed3 ("ems_usb: Added support for EMS CPC-USB/ARM7 CAN/USB interface")
Cc: stable@vger.kernel.org
Signed-off-by: Marc Kleine-Budde <mkl@pengutronix.de>
[Denis Arefev: adapted for 5.10: use get_can_dlc() instead of
 can_cc_dlc2len(), the latter was introduced in 6.x along with
 include/linux/can/length.h; get_can_dlc() has identical semantics
 for classic CAN frames (min(dlc, CAN_MAX_DLEN))]
Signed-off-by: Denis Arefev <arefev@swemel.ru>
---
Backport fix for CVE-2026-74460 
Link: https://nvd.nist.gov/vuln/detail/CVE-2026-74460
---
 drivers/net/can/usb/ems_usb.c | 43 +++++++++++++++++++++++++++++++++++
 1 file changed, 43 insertions(+)

diff --git a/drivers/net/can/usb/ems_usb.c b/drivers/net/can/usb/ems_usb.c
index 65aa1100e894..a645962da37a 100644
--- a/drivers/net/can/usb/ems_usb.c
+++ b/drivers/net/can/usb/ems_usb.c
@@ -402,6 +402,40 @@ static void ems_usb_rx_err(struct ems_usb *dev, struct ems_cpc_msg *msg)
 	netif_rx(skb);
 }
 
+static bool ems_usb_rx_msg_len_valid(struct ems_cpc_msg *msg)
+{
+	size_t len = msg->length;
+	size_t can_len;
+
+	switch (msg->type) {
+	case CPC_MSG_TYPE_CAN_STATE:
+		return len >= sizeof(msg->msg.can_state);
+
+	case CPC_MSG_TYPE_CAN_FRAME:
+	case CPC_MSG_TYPE_EXT_CAN_FRAME:
+	case CPC_MSG_TYPE_RTR_FRAME:
+	case CPC_MSG_TYPE_EXT_RTR_FRAME:
+		if (len < CPC_CAN_MSG_MIN_SIZE)
+			return false;
+
+		if (msg->type == CPC_MSG_TYPE_RTR_FRAME ||
+		    msg->type == CPC_MSG_TYPE_EXT_RTR_FRAME)
+			return true;
+
+		can_len = get_can_dlc(msg->msg.can_msg.length & 0xf);
+		return len >= CPC_CAN_MSG_MIN_SIZE + can_len;
+
+	case CPC_MSG_TYPE_CAN_FRAME_ERROR:
+		return len >= sizeof(msg->msg.error);
+
+	case CPC_MSG_TYPE_OVERRUN:
+		return len >= sizeof(msg->msg.overrun);
+
+	default:
+		return true;
+	}
+}
+
 /*
  * callback for bulk IN urb
  */
@@ -444,6 +478,15 @@ static void ems_usb_read_bulk_callback(struct urb *urb)
 			}
 
 			msg = (struct ems_cpc_msg *)&ibuf[start];
+			if (msg->length >
+			    urb->actual_length - start - CPC_MSG_HEADER_LEN) {
+				netdev_err(netdev, "format error\n");
+				break;
+			}
+			if (!ems_usb_rx_msg_len_valid(msg)) {
+				netdev_err(netdev, "format error\n");
+				break;
+			}
 
 			switch (msg->type) {
 			case CPC_MSG_TYPE_CAN_STATE:
-- 
2.43.0