[PATCH net] nfc: port100: reject frames whose declared length exceeds the received data

port100_recv_response() passes the URB transfer buffer to
port100_rx_frame_is_valid(), which checksums le16_to_cpu(frame->datalen)
bytes of frame->data. datalen is a 16-bit field supplied by the device
and is never checked against the number of bytes actually received
(urb->actual_length), so a device reporting a datalen larger than the
received frame makes port100_data_checksum() read out of bounds past the
transfer buffer.

Reject a response whose declared frame size does not fit the received
length before validating it.

Found by 0sec (https://0sec.ai) using automated source analysis; the
missing bound is evident from source. Compile-tested.

Fixes: 562d4d59b8a1 ("NFC: Sony Port-100 Series driver")
Cc: [email protected]
Assisted-by: 0sec:claude-opus-4-8
Signed-off-by: Doruk Tan Ozturk <[email protected]>
---
 drivers/nfc/port100.c | 7 +++++++
 1 file changed, 7 insertions(+)

diff --git a/drivers/nfc/port100.c b/drivers/nfc/port100.c
index 5ae61d7ebcfe..30a4e09875d3 100644
--- a/drivers/nfc/port100.c
+++ b/drivers/nfc/port100.c
@@ -636,6 +636,13 @@ static void port100_recv_response(struct urb *urb)
 
 	in_frame = dev->in_urb->transfer_buffer;
 
+	if (urb->actual_length < PORT100_FRAME_HEADER_LEN ||
+	    urb->actual_length < port100_rx_frame_size(in_frame)) {
+		nfc_err(&dev->interface->dev, "Received a truncated frame\n");
+		cmd->status = -EIO;
+		goto sched_wq;
+	}
+
 	if (!port100_rx_frame_is_valid(in_frame)) {
 		nfc_err(&dev->interface->dev, "Received an invalid frame\n");
 		cmd->status = -EIO;
-- 
2.43.0