Re: [PATCH] Input: pegasus-notetaker - fix out-of-bounds access vulnerability in pegasus_parse_packet() function of the pegasus driver

[Dmitry Torokhov]

Hi,

On Tue, Oct 07, 2025 at 05:41:32PM -0400, pip-izony wrote:
> From: Seungjin Bae <eeodqql09@xxxxxxxxx>
> 
> In the pegasus_notetaker driver, the pegasus_probe() function allocates
> the URB transfer buffer using the wMaxPacketSize value from
> the endpoint descriptor. An attacker can use a malicious USB descriptor
> to force the allocation of a very small buffer.
> 
> Subsequently, if the device sends an interrupt packet with a specific
> pattern (e.g., where the first byte is 0x80 or 0x42),
> the pegasus_parse_packet() function parses the packet without checking
> the allocated buffer size. This leads to an out-of-bounds memory access,
> which could result in a system panic.
> 
> Fixes: 948bf18 ("Input: remove third argument of usb_maxpacket()")
> Signed-off-by: Seungjin Bae <eeodqql09@xxxxxxxxx>
> ---
>  drivers/input/tablet/pegasus_notetaker.c | 5 +++++
>  1 file changed, 5 insertions(+)
> 
> diff --git a/drivers/input/tablet/pegasus_notetaker.c b/drivers/input/tablet/pegasus_notetaker.c
> index 8d6b71d59793..6c4199712a4e 100644
> --- a/drivers/input/tablet/pegasus_notetaker.c
> +++ b/drivers/input/tablet/pegasus_notetaker.c
> @@ -311,6 +311,11 @@ static int pegasus_probe(struct usb_interface *intf,
>  	}
>  
>  	pegasus->data_len = usb_maxpacket(dev, pipe);
> +    if (pegasus->data_len < 5) {

The packet size is actually 6 (status + color + 2-byte X coordinate +
2-byte Y coordinate) so there's still off-by-one error.

I fixed it up and applied.

Thanks.

-- 
Dmitry