[PATCH 2/2] Xi: fix touch event selction conflicts (#57301)

[Peter Hutterer]

There are limits on which client may select for touch events on a given
window, with restrictions being that no two clients can select on the same
device, but narrower selections are allowed, i.e. if one client has
XIAllDevices, a second client may still select for device X.

The current code had a dependency on which client selected first and which
device, resulting in inconsistencies when selecting for events. Fix that,
responding with the right errors regardless of who selected what first.

X.Org Bug 57301 <http://bugs.freedesktop.org/show_bug.cgi?id=57301>

Signed-off-by: Peter Hutterer <peter.hutterer at who-t.net>
---
I'm not 100% myself on what the right thing to do is for XIAllDevices and
XIAllMasterDevices. A client selecting for the former would (with this
patch) essentially get overridden by a client XIAllMasterDevices, with touch
events only going to the second one then.

If we would limit that to either XIAllDevices or XIAllMasterDevices, not
both, we'd definitely need to add this to the protocol.

 Xi/xiselectev.c | 80 ++++++++++++++++++++++++++++++++++++++++-----------------
 1 file changed, 56 insertions(+), 24 deletions(-)

diff --git a/Xi/xiselectev.c b/Xi/xiselectev.c
index ab1b624..45a996e 100644
--- a/Xi/xiselectev.c
+++ b/Xi/xiselectev.c
@@ -37,6 +37,57 @@
 #include "xiselectev.h"
 
 /**
+ * Ruleset:
+ * - if A has XIAllDevices, B may select on device X
+ * - If A has XIAllDevices, B may select on XIAllMasterDevices
+ * - If A has XIAllMasterDevices, B may select on device X
+ * - If A has XIAllMasterDevices, B may select on XIAllDevices
+ * - if A has device X, B may select on XIAllDevices/XIAllMasterDevices
+ */
+static int check_for_touch_selection_conflicts(ClientPtr B, WindowPtr win, int deviceid)
+{
+    OtherInputMasks *inputMasks = wOtherInputMasks(win);
+    InputClients *A = NULL;
+
+    if (inputMasks)
+        A = inputMasks->inputClients;
+    for (; A; A = A->next) {
+        DeviceIntPtr tmp;
+
+        if (CLIENT_ID(A->resource) == B->index)
+            continue;
+
+        if (deviceid == XIAllDevices)
+            tmp = inputInfo.all_devices;
+        else if (deviceid == XIAllMasterDevices)
+            tmp = inputInfo.all_master_devices;
+        else
+            dixLookupDevice(&tmp, deviceid, serverClient, DixReadAccess);
+        if (!tmp)
+            return BadImplementation;       /* this shouldn't happen */
+
+        /* A has XIAllDevices */
+        if (xi2mask_isset_for_device(A->xi2mask, inputInfo.all_devices, XI_TouchBegin)) {
+            if (deviceid == XIAllDevices)
+                return BadAccess;
+        }
+
+        /* A has XIAllMasterDevices */
+        if (xi2mask_isset_for_device(A->xi2mask, inputInfo.all_master_devices, XI_TouchBegin)) {
+            if (deviceid == XIAllMasterDevices)
+                return BadAccess;
+        }
+
+        /* A has this device */
+        if (xi2mask_isset_for_device(A->xi2mask, tmp, XI_TouchBegin))
+            return BadAccess;
+    }
+
+    return Success;
+}
+
+
+/**
  * Check the given mask (in len bytes) for invalid mask bits.
  * Invalid mask bits are any bits above XI2LastEvent.
  *
@@ -169,30 +220,11 @@ ProcXISelectEvents(ClientPtr client)
              * same devices, including master devices.
              * XXX: This breaks if a device goes from floating to attached. */
             if (BitIsOn(bits, XI_TouchBegin)) {
-                OtherInputMasks *inputMasks = wOtherInputMasks(win);
-                InputClients *iclient = NULL;
-
-                if (inputMasks)
-                    iclient = inputMasks->inputClients;
-                for (; iclient; iclient = iclient->next) {
-                    DeviceIntPtr tmp;
-
-                    if (CLIENT_ID(iclient->resource) == client->index)
-                        continue;
-
-                    if (evmask->deviceid == XIAllDevices)
-                        tmp = inputInfo.all_devices;
-                    else if (evmask->deviceid == XIAllMasterDevices)
-                        tmp = inputInfo.all_master_devices;
-                    else
-                        dixLookupDevice(&tmp, evmask->deviceid, serverClient,
-                                        DixReadAccess);
-                    if (!tmp)
-                        return BadImplementation;       /* this shouldn't happen */
-
-                    if (xi2mask_isset(iclient->xi2mask, tmp, XI_TouchBegin))
-                        return BadAccess;
-                }
+                rc = check_for_touch_selection_conflicts(client,
+                                                         win,
+                                                         evmask->deviceid);
+                if (rc != Success)
+                    return rc;
             }
         }
 
-- 
1.7.11.7