linux-kernel - Re: [PATCH] HID: multitouch: fix integer overflow in set

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Message-ID: <914ff45b-2260-42c0-9ccf-a3efd667d4f5@kernel.org>
Date: Thu, 24 Jul 2025 08:58:40 +0200
From: Jiri Slaby <jirislaby@...nel.org>
To: Qasim Ijaz <qasdev00@...il.com>, jikos@...nel.org, bentiss@...nel.org
Cc: linux-input@...r.kernel.org, linux-kernel@...r.kernel.org,
 stable@...r.kernel.org
Subject: Re: [PATCH] HID: multitouch: fix integer overflow in set_abs()

On 23. 07. 25, 19:36, Qasim Ijaz wrote:
> It is possible for a malicious HID device to trigger a signed integer
> overflow (undefined behaviour) in set_abs() in the following expression
> by supplying bogus logical maximum and minimum values:
> 	
> 	int fuzz = snratio ? (fmax - fmin) / snratio : 0;
> 
> For example, if the logical_maximum is INT_MAX and logical_minimum is -1
> then (fmax - fmin) resolves to INT_MAX + 1, which does not fit in a 32-bit
> signed int, so the subtraction overflows.

The question is if it matters with -fwrapv?

> Fix this by computing the
> difference in a 64 bit context.
> 
> Fixes: 5519cab477b6 ("HID: hid-multitouch: support for PixCir-based panels")
> Cc: stable@...r.kernel.org
> Signed-off-by: Qasim Ijaz <qasdev00@...il.com>
> ---
>   drivers/hid/hid-multitouch.c | 3 ++-
>   1 file changed, 2 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/hid/hid-multitouch.c b/drivers/hid/hid-multitouch.c
> index 22c6314a8843..687638ed6d0f 100644
> --- a/drivers/hid/hid-multitouch.c
> +++ b/drivers/hid/hid-multitouch.c
> @@ -540,7 +540,8 @@ static void set_abs(struct input_dev *input, unsigned int code,
>   {
>   	int fmin = field->logical_minimum;
>   	int fmax = field->logical_maximum;
> -	int fuzz = snratio ? (fmax - fmin) / snratio : 0;
> +	s64 diff = (s64)fmax - (s64)fmin;
> +	int fuzz = snratio ? (int)div_s64(diff, snratio) : 0;
>   	input_set_abs_params(input, code, fmin, fmax, fuzz, 0);
>   	input_abs_set_res(input, code, hidinput_calc_abs_res(field, code));
>   }

-- 
js
suse labs