Xi: Unify checking for invalid bits in grab masks.

Bits above XI2LASTEVENT are invalid and cause in BadValues. These checks
must be performed anywhere where a mask_len parameter is given.

This patch also adds the missing checks to grab masks.

Signed-off-by: Peter Hutterer <peter.hutterer@who-t.net>

Xi/xigrabdev.c

@@ -39,6 +39,7 @@
 #include <X11/extensions/XI2proto.h>
 
 #include "exglobals.h" /* BadDevice */
+#include "exevents.h"
 #include "xigrabdev.h"
 
 int
@@ -78,6 +79,10 @@ ProcXIGrabDevice(ClientPtr client)
     if (!IsMaster(dev))
         stuff->paired_device_mode = GrabModeAsync;
 
+    if (XICheckInvalidMaskBits((unsigned char*)&stuff[1],
+                               stuff->mask_len * 4) != Success)
+        return BadValue;
+
     mask_len = min(sizeof(mask.xi2mask[stuff->deviceid]), stuff->mask_len * 4);
     memset(mask.xi2mask, 0, sizeof(mask.xi2mask));
     memcpy(mask.xi2mask, (char*)&stuff[1], mask_len);

Xi/xipassivegrab.c

@@ -118,15 +118,9 @@ ProcXIPassiveGrabDevice(ClientPtr client)
         return BadValue;
     }
 
-    if ((stuff->mask_len * 4) > XI2LASTEVENT)
-    {
-        unsigned char *bits = (unsigned char*)&stuff[1];
-        for (i = XI2LASTEVENT; i < stuff->mask_len * 4; i++)
-        {
-            if (BitIsOn(bits, i))
-                return BadValue;
-        }
-    }
+    if (XICheckInvalidMaskBits((unsigned char*)&stuff[1],
+                               stuff->mask_len * 4) != Success)
+        return BadValue;
 
     mask_len = min(sizeof(mask.xi2mask[stuff->deviceid]), stuff->mask_len * 4);
     memset(mask.xi2mask, 0, sizeof(mask.xi2mask));

Xi/xiselectev.c

@@ -36,6 +36,25 @@
 
 #include "xiselectev.h"
 
+/**
+ * Check the given mask (in len bytes) for invalid mask bits.
+ * Invalid mask bits are any bits above XI2LastEvent.
+ *
+ * @return BadValue if at least one invalid bit is set or Success otherwise.
+ */
+int XICheckInvalidMaskBits(unsigned char *mask, int len)
+{
+    if (len >= XIMaskLen(XI2LASTEVENT))
+    {
+        int i;
+        for (i = XI2LASTEVENT + 1; i < len * 8; i++)
+            if (BitIsOn(mask, i))
+                return BadValue;
+    }
+
+    return Success;
+}
+
 int
 SProcXISelectEvents(ClientPtr client)
 {
@@ -63,7 +82,7 @@ SProcXISelectEvents(ClientPtr client)
 int
 ProcXISelectEvents(ClientPtr client)
 {
-    int rc, num_masks, i;
+    int rc, num_masks;
     WindowPtr win;
     DeviceIntPtr dev;
     DeviceIntRec dummy;
@@ -122,15 +141,9 @@ ProcXISelectEvents(ClientPtr client)
                 return BadValue;
         }
 
-        if ((evmask->mask_len * 4) >= (XI2LASTEVENT + 8)/8)
-        {
-            unsigned char *bits = (unsigned char*)&evmask[1];
-            for (i = XI2LASTEVENT + 1; i < evmask->mask_len * 4; i++)
-            {
-                if (BitIsOn(bits, i))
-                    return BadValue;
-            }
-        }
+        if (XICheckInvalidMaskBits((unsigned char*)&evmask[1],
+                                   evmask->mask_len * 4) != Success)
+            return BadValue;
 
         evmask = (xXIEventMask*)(((unsigned char*)evmask) + evmask->mask_len * 4);
         evmask++;

include/exevents.h

@@ -309,4 +309,7 @@ extern void
 XISetEventMask(DeviceIntPtr dev, WindowPtr win, ClientPtr client,
                            unsigned int len, unsigned char* mask);
 
+extern int
+XICheckInvalidMaskBits(unsigned char *mask, int len);
+
 #endif /* EXEVENTS_H */