[PATCH v2] HID: ft260: validate i2c input report length

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

Add two checks to ft260_raw_event() to prevent out-of-bounds reads
from malicious or malfunctioning devices:

First, reject reports shorter than the 2-byte header (report ID +
length fields). Without this, even accessing xfer->length on a
1-byte report is an OOB read.

Second, validate xfer->length against the actual data capacity of
the received HID report. Each I2C data report ID (0xD0 through
0xDE) defines a different report size in the HID descriptor, so the
available payload varies per report. A corrupted length field could
cause memcpy to read beyond the report buffer.

Reported-by: Sebastián Josué Alba Vives <sebasjosue84@gmail.com>
Signed-off-by: Michael Zaidman <michael.zaidman@gmail.com>
---
Changes in v2:
- Add minimum report size check before accessing header fields to
  prevent OOB read on truncated reports (size < 2)

Tested on FT260 with I2C-attached EEPROM (24c02) behind PCA9548
mux switches. Verified reads of various sizes (1-4 bytes using
report ID 0xD0, and larger reads using higher report IDs) with
debug tracing enabled, confirming xfer->length is correctly
validated against the HID report size for each report ID.
---
 drivers/hid/hid-ft260.c | 16 ++++++++++++++--
 1 file changed, 14 insertions(+), 2 deletions(-)

diff --git a/drivers/hid/hid-ft260.c b/drivers/hid/hid-ft260.c
index 333341e80b0e..70e2eedb465a 100644
--- a/drivers/hid/hid-ft260.c
+++ b/drivers/hid/hid-ft260.c
@@ -1068,10 +1068,22 @@ static int ft260_raw_event(struct hid_device *hdev, struct hid_report *report,
 	struct ft260_device *dev = hid_get_drvdata(hdev);
 	struct ft260_i2c_input_report *xfer = (void *)data;
 
+	if (size < offsetof(struct ft260_i2c_input_report, data)) {
+		hid_err(hdev, "short report %d\n", size);
+		return -1;
+	}
+
 	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