[PATCH] Xi: Fix master button update when slave buttons are mapped. #24887

[Eoghan Sherry]

It is currently assumed that an event button delieved to a master device
corresponds to the slave button states. However, the event button is a
logical (mapped) slave button and slave button states correspond to
physical (unmapped) slave buttons. This leads to incorrect update of the
master button state and incorrect events devlivered to clients. Fix the
situation by taking the slave button map into account when querying a
slave button state.

Fixes: https://bugs.freedesktop.org/show_bug.cgi?id=24887

Signed-off-by: Eoghan Sherry <ejsherry at gmail.com>
---

This bug seems to have been introduced a couple of years ago by commit
cfcb3da7.  It probably affects xserver 1.5.0 onward.  The bug report
describes a method of reproduction.  I came across it by using mouse
chords (acme user here) with the mouse mapped for my left hand.

A couple of notes about the proposed fix.  The reverse map of slave
buttons (logical to physical) could be precomputed, not sure if it's
worthwhile.  Also, maybe the button state of a device could be changed
to correspond to logical buttons, not sure of all the consequences or
if it would even work.

Finally, this is my first contact with X.org; call me out on things I
get wrong with the process.

Eoghan

 Xi/exevents.c |    6 ++++--
 1 files changed, 4 insertions(+), 2 deletions(-)

diff --git a/Xi/exevents.c b/Xi/exevents.c
index d57265e..8615fd4 100644
--- a/Xi/exevents.c
+++ b/Xi/exevents.c
@@ -870,8 +870,10 @@ UpdateDeviceState(DeviceIntPtr device, DeviceEvent* event)
                     continue;
                 if (!sd->button)
                     continue;
-                if (button_is_down(sd, key, BUTTON_PROCESSED))
-                    return DONT_PROCESS;
+                for (i = 1; i <= sd->button->numButtons; i++)
+                    if (sd->button->map[i] == key &&
+                        button_is_down(sd, i, BUTTON_PROCESSED))
+                        return DONT_PROCESS;
             }
         }
         set_button_up(device, key, BUTTON_PROCESSED);
-- 
1.7.0.4