[PATCH] HID: ft260: validate i2c input report length

[Michael Zaidman <michael.zaidman@gmail.com>]

Validate xfer->length against the actual HID report size in
ft260_raw_event() before using it as the memcpy length. A malicious
or malfunctioning device could send a report with xfer->length
exceeding the data actually present in the HID report, causing an
out-of-bounds read.

Each I2C data report ID (0xD0 through 0xDE) defines a different
report size in the HID descriptor, so the available payload varies
per report. Validate against the actual received report size rather
than a fixed maximum to avoid breaking valid short transfers.

Reported-by: Sebastián Josué Alba Vives <sebasjosue84@gmail.com>
Signed-off-by: Michael Zaidman <michael.zaidman@gmail.com>
---
Tested on FT260 with I2C-attached EEPROM (24c02) behind PCA9548
mux switches. Verified short reads (1-4 bytes, report ID 0xD0)
and multi-report reads with debug tracing enabled, confirming
xfer->length is correctly validated against the HID report size
for each report ID.
---
 drivers/hid/hid-ft260.c | 11 +++++++++--
 1 file changed, 9 insertions(+), 2 deletions(-)

diff --git a/drivers/hid/hid-ft260.c b/drivers/hid/hid-ft260.c
index 333341e80b0e..b31c43353249 100644
--- a/drivers/hid/hid-ft260.c
+++ b/drivers/hid/hid-ft260.c
@@ -1070,8 +1070,15 @@ static int ft260_raw_event(struct hid_device *hdev, struct hid_report *report,
 
 	if (xfer->report >= FT260_I2C_REPORT_MIN &&
 	    xfer->report <= FT260_I2C_REPORT_MAX) {
-		ft260_dbg("i2c resp: rep %#02x len %d\n", xfer->report,
-			  xfer->length);
+		ft260_dbg("i2c resp: rep %#02x len %d size %d\n",
+			  xfer->report, xfer->length, size);
+
+		if (xfer->length > size -
+		    offsetof(struct ft260_i2c_input_report, data)) {
+			hid_err(hdev, "report %#02x: length %d exceeds HID report size\n",
+				xfer->report, xfer->length);
+			return -1;
+		}
 
 		if ((dev->read_buf == NULL) ||
 		    (xfer->length > dev->read_len - dev->read_idx)) {
-- 
2.25.1