linux-kernel - Re: [PATCH] HID: magicmouse: prevent division by 0 on scroll

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Message-ID: <nycvar.YFH.7.76.2111191554340.16505@cbobk.fhfr.pm>
Date:   Fri, 19 Nov 2021 15:54:42 +0100 (CET)
From:   Jiri Kosina <jikos@...nel.org>
To:     Claudia Pellegrino <linux@...llegrino.de>
cc:     Benjamin Tissoires <benjamin.tissoires@...hat.com>,
        José Expósito <jose.exposito89@...il.com>,
        linux-input@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] HID: magicmouse: prevent division by 0 on scroll

On Sun, 14 Nov 2021, Claudia Pellegrino wrote:

> In hid_magicmouse, if the user has set scroll_speed to a value between
> 55 and 63 and scrolls seven times in quick succession, the
> step_hr variable in the magicmouse_emit_touch function becomes 0.
> 
> That causes a division by zero further down in the function when
> it does `step_x_hr /= step_hr`.
> 
> To reproduce, create `/etc/modprobe.d/hid_magicmouse.conf` with the
> following content:
> 
> ```
> options hid_magicmouse scroll_acceleration=1 scroll_speed=55
> ```
> 
> Then reboot, connect a Magic Mouse and scroll seven times quickly.
> The system will freeze for a minute, and after that `dmesg` will
> confirm that a division by zero occurred.
> 
> Enforce a minimum of 1 for the variable so the high resolution
> step count can never reach 0 even at maximum scroll acceleration.
> 
> Fixes: d4b9f10a0eb6 ("HID: magicmouse: enable high-resolution scroll")
> 
> Signed-off-by: Claudia Pellegrino <linux@...llegrino.de>

Applied, thank you.

-- 
Jiri Kosina
SUSE Labs