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

[Jiri Kosina]

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@xxxxxxxxxxxxxx>

Applied, thank you.

-- 
Jiri Kosina
SUSE Labs