[PATCH v3] Bluetooth: bfusb: Fix buffer over-read in rx processing loop

[pip-izony <eeodqql09@gmail.com>]

From: Seungjin Bae <eeodqql09@gmail.com>

The bfusb_rx_complete() function parses incoming URB data in a while loop.
The logic does not sufficiently validate the remaining buffer size(count)
across loop iterations, which can lead to a buffer over-read.

For example, with 4-bytes remaining buffer, if the first iteration takes
the `hdr & 0x4000` branch, 2-bytes are consumed. On the next iteration,
only 2-bytes remain, but the else branch is trying to access the third
byte(buf[2]). This causes an out-of-bounds read and a potential kernel
panic.

This patch fixes the vulnerability by adding checks to ensure enough
data remains in the buffer before it is accessed.

Fixes: 1da177e4c3f4 ("Linux-2.6.12-rc2")
Signed-off-by: Seungjin Bae <eeodqql09@gmail.com>
---
 v1 -> v2: Fixing the error function name
 v2 -> v3: Addressing feedback from Paul Menzel

 drivers/bluetooth/bfusb.c | 6 ++++++
 1 file changed, 6 insertions(+)

diff --git a/drivers/bluetooth/bfusb.c b/drivers/bluetooth/bfusb.c
index 8df310983bf6..90ca5ab2acc3 100644
--- a/drivers/bluetooth/bfusb.c
+++ b/drivers/bluetooth/bfusb.c
@@ -360,6 +360,12 @@ static void bfusb_rx_complete(struct urb *urb)
 			count -= 2;
 			buf   += 2;
 		} else {
+			if (count < 3) {
+				bt_dev_err(data->hdev,
+				       "block header is too short (count=%d, expected=3)",
+				       count);
+				break;
+			}
 			len = (buf[2] == 0) ? 256 : buf[2];
 			count -= 3;
 			buf   += 3;
-- 
2.43.0