[PATCH] mi: don't process events from disabled devices (#77884)

[Maarten Lankhorst]

op 20-05-14 06:32, Peter Hutterer schreef:
> Once a device is disabled, it doesn't have a sprite pointer anymore. If an
> event is still in the queue and processed after DisableDevice finished, a
> dereference causes a crash. Example backtrace (crash forced by injecting an
> event at the right time):
>
> (EE) 0: /opt/xorg/bin/Xorg (OsSigHandler+0x3c) [0x48d334]
> (EE) 1: /lib64/libpthread.so.0 (__restore_rt+0x0) [0x37fcc0f74f]
> (EE) 2: /opt/xorg/bin/Xorg (mieqMoveToNewScreen+0x38) [0x609240]
> (EE) 3: /opt/xorg/bin/Xorg (mieqProcessDeviceEvent+0xd4) [0x609389]
> (EE) 4: /opt/xorg/bin/Xorg (mieqProcessInputEvents+0x206) [0x609720]
> (EE) 5: /opt/xorg/bin/Xorg (ProcessInputEvents+0xd) [0x4aeb58]
> (EE) 6: /opt/xorg/bin/Xorg (xf86VTSwitch+0x1a6) [0x4af457]
> (EE) 7: /opt/xorg/bin/Xorg (xf86Wakeup+0x2bf) [0x4af0a7]
> (EE) 8: /opt/xorg/bin/Xorg (WakeupHandler+0x83) [0x4445cb]
> (EE) 9: /opt/xorg/bin/Xorg (WaitForSomething+0x3fe) [0x491bf6]
> (EE) 10: /opt/xorg/bin/Xorg (Dispatch+0x97) [0x435748]
> (EE) 11: /opt/xorg/bin/Xorg (dix_main+0x61d) [0x4438a9]
> (EE) 12: /opt/xorg/bin/Xorg (main+0x28) [0x49ba28]
> (EE) 13: /lib64/libc.so.6 (__libc_start_main+0xf5) [0x37fc821d65]
> (EE) 14: /opt/xorg/bin/Xorg (_start+0x29) [0x425e69]
> (EE) 15: ? (?+0x29) [0x29]
>
> xf86VTSwitch() calls ProcessInputEvents() before disabling a device, and
> DisableDevice() calls mieqProcessInputEvents() again when flushing touches and
> button events. Between that and disabling the device (which causes new events
> to be refused) there is a window where events may be triggered and enqueued.
> On the next call to PIE that event is processed on a now defunct device,
> causing the crash.
>
> The simplest fix to this is to discard events from disabled devices. We flush
> the queue often enough before disabling that when we get here, we really don't
> care about the events from this device.
>
> X.Org Bug 77884 <http://bugs.freedesktop.org/show_bug.cgi?id=77884>
> ---
>   mi/mieq.c | 4 ++++
>   1 file changed, 4 insertions(+)
>
> diff --git a/mi/mieq.c b/mi/mieq.c
> index 4c07480..188a0b0 100644
> --- a/mi/mieq.c
> +++ b/mi/mieq.c
> @@ -515,6 +515,10 @@ mieqProcessDeviceEvent(DeviceIntPtr dev, InternalEvent *event, ScreenPtr screen)
>   
>       verify_internal_event(event);
>   
> +    /* refuse events from disabled devices */
> +    if (!dev->enabled)
> +        return 0;
> +
>       /* Custom event handler */
>       handler = miEventQueue.handlers[event->any.type];
>   
A modified version with if (dev && !dev->enabled) return 0; works for me, so

Reported-and-Tested-By: Maarten Lankhorst <maarten.lankhorst at canonical.com>