From a1091118e0d6d84c2fdb94e6c397ac790bfb9dd6 Mon Sep 17 00:00:00 2001 From: Claudia Pellegrino Date: Sun, 14 Nov 2021 03:53:27 +0100 Subject: [PATCH] HID: magicmouse: prevent division by 0 on scroll MIME-Version: 1.0 Content-Type: text/plain; charset=utf8 Content-Transfer-Encoding: 8bit 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 Tested-by: José Expósito Signed-off-by: Jiri Kosina --- drivers/hid/hid-magicmouse.c | 7 +++++-- 1 file changed, 5 insertions(+), 2 deletions(-) diff --git a/drivers/hid/hid-magicmouse.c b/drivers/hid/hid-magicmouse.c index 686788ebf3e1..d7687ce70614 100644 --- a/drivers/hid/hid-magicmouse.c +++ b/drivers/hid/hid-magicmouse.c @@ -256,8 +256,11 @@ static void magicmouse_emit_touch(struct magicmouse_sc *msc, int raw_id, u8 *tda unsigned long now = jiffies; int step_x = msc->touches[id].scroll_x - x; int step_y = msc->touches[id].scroll_y - y; - int step_hr = ((64 - (int)scroll_speed) * msc->scroll_accel) / - SCROLL_HR_STEPS; + int step_hr = + max_t(int, + ((64 - (int)scroll_speed) * msc->scroll_accel) / + SCROLL_HR_STEPS, + 1); int step_x_hr = msc->touches[id].scroll_x_hr - x; int step_y_hr = msc->touches[id].scroll_y_hr - y; -- 2.39.5