[PATCH 1/4] dix: fix crash when removing devices on a buttonless MD pointer (#29669)

[Peter Hutterer]

If the master does not have a button class, recalculating the number of
buttons required for this master dereferences a NULL pointer. Guard against
this, if the master pointer doesn't have a button class, it doesn't need to
update it's number of buttons.

Reproducible:
Two devices on the same master, device NB with axes but no buttons, device
A+B with axes and button .
If NB was the last one to send an event through the master when A+B is
removed from the server, master->button is NULL and leads to the above
NULL-pointer dereference.

X.Org Bug 29669 <http://bugs.freedesktop.org/show_bug.cgi?id=29669>

Signed-off-by: Peter Hutterer <peter.hutterer at who-t.net>
---
 dix/devices.c |    2 +-
 1 files changed, 1 insertions(+), 1 deletions(-)

diff --git a/dix/devices.c b/dix/devices.c
index 2e65a04..0bd9b75 100644
--- a/dix/devices.c
+++ b/dix/devices.c
@@ -2336,7 +2336,7 @@ RecalculateMasterButtons(DeviceIntPtr slave)
         maxbuttons = max(maxbuttons, dev->button->numButtons);
     }
 
-    if (master->button->numButtons != maxbuttons)
+    if (master->button && master->button->numButtons != maxbuttons)
     {
         int i;
         DeviceChangedEvent event;
-- 
1.7.2.2