linux-kernel - Re: [PATCH v4] Bluetooth: bfusb: Fix buffer over-read in rx processing loop

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Message-ID: <CABBYNZLgOpam+34S-VA3pVYVfwYRxBSCLa8FU66rrB57ogUv=w@mail.gmail.com>
Date: Thu, 9 Oct 2025 13:14:23 -0400
From: Luiz Augusto von Dentz <luiz.dentz@...il.com>
To: pip-izony <eeodqql09@...il.com>
Cc: Marcel Holtmann <marcel@...tmann.org>, Kyungtae Kim <Kyungtae.Kim@...tmouth.edu>, 
	linux-kernel@...r.kernel.org, linux-bluetooth@...r.kernel.org
Subject: Re: [PATCH v4] Bluetooth: bfusb: Fix buffer over-read in rx
 processing loop

Hi Pip-Izony,

On Thu, Oct 9, 2025 at 12:51 PM pip-izony <eeodqql09@...il.com> wrote:
>
> From: Seungjin Bae <eeodqql09@...il.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@...il.com>

This is sort of useless if you ask me, this driver is never used in
practice, and even in case someone still have the only model it
handles  USB_DEVICE(0x057c, 0x2200) I bet it would have been easier to
just add it to btusb since it appears to be using the standard class
as well.

> ---
>   v1 -> v2: Fixing the error function name
>   v2 -> v3: Addressing feedback from Paul Menzel
>   v3 -> v4: Improving the error message for the block header count
>
>  drivers/bluetooth/bfusb.c | 5 +++++
>  1 file changed, 5 insertions(+)
>
> diff --git a/drivers/bluetooth/bfusb.c b/drivers/bluetooth/bfusb.c
> index 8df310983bf6..02ba16775004 100644
> --- a/drivers/bluetooth/bfusb.c
> +++ b/drivers/bluetooth/bfusb.c
> @@ -360,6 +360,11 @@ static void bfusb_rx_complete(struct urb *urb)
>                         count -= 2;
>                         buf   += 2;
>                 } else {
> +                       if (count < 3) {
> +                               bt_dev_err(data->hdev, "block header count %d < 3 (too short)",
> +                                          count);
> +                               break;
> +                       }
>                         len = (buf[2] == 0) ? 256 : buf[2];
>                         count -= 3;
>                         buf   += 3;
> --
> 2.43.0
>


-- 
Luiz Augusto von Dentz