From f399919e13c994452f7219163b2a4b1fa015242e Mon Sep 17 00:00:00 2001 From: Peter Hutterer Date: Fri, 12 Aug 2016 13:59:56 +1000 Subject: [PATCH] xfree86: lock input during PreInit This is a problem for the libinput driver that uses the same context across multiple devices. The driver may be halfway through setting up an input device (and the only way to do so is to add it to libinput) when the input thread comes in an reads events. This then causes mayhem when data is dereferenced that hasn't been set up yet. In my case the cause was the call to libinput_path_remove_device() inside preinit racing with evdev_dispatch_device() handling of ENODEV. The sequence was: - thread 2 gets an event and calls evdev_dispatch_device() - thread 1 calls libinput_path_remove_device() which sets the device->source to NULL - thread 2 reads from the fd, gets ENODEV and now removes the device->source, dereferencing the null-pointer This is the one I could reproduce the most, but there are other potential pitfalls that affect any driver that uses the same fd for multiple devices. Avoid all this and wrap PreInit into the lock. Signed-off-by: Peter Hutterer Reviewed-by: Keith Packard --- hw/xfree86/common/xf86Xinput.c | 2 ++ 1 file changed, 2 insertions(+) diff --git a/hw/xfree86/common/xf86Xinput.c b/hw/xfree86/common/xf86Xinput.c index 3e6a264d0..538b11027 100644 --- a/hw/xfree86/common/xf86Xinput.c +++ b/hw/xfree86/common/xf86Xinput.c @@ -926,7 +926,9 @@ xf86NewInputDevice(InputInfoPtr pInfo, DeviceIntPtr *pdev, BOOL enable) xf86AddInput(drv, pInfo); + input_lock(); rval = drv->PreInit(drv, pInfo, 0); + input_unlock(); if (rval != Success) { xf86Msg(X_ERROR, "PreInit returned %d for \"%s\"\n", rval, pInfo->name);