Xi: fix modifier offset in XIPassiveGrab swapping function

The request is followed by mask_len 4-byte units, then followed by the actual
modifiers.

Also fix up the swapping test, which had the same issue.

Reported-by: Alan Coopersmith <alan.coopersmith@oracle.com>
Signed-off-by: Peter Hutterer <peter.hutterer@who-t.net>
Reviewed-by: Alan Coopersmith <alan.coopersmith@oracle.com>
(cherry picked from commit 76b3be75b62657e346731444736f7e4d200beb5b)

Conflicts:
	test/xi2/protocol-xipassivegrabdevice.c

2 files changed, 9 insertions, 2 deletions

diff --git a/Xi/xipassivegrab.c b/Xi/xipassivegrab.c
index eccec0ab8..8aba97781 100644
--- a/Xi/xipassivegrab.c
+++ b/Xi/xipassivegrab.c
@@ -63,7 +63,7 @@ SProcXIPassiveGrabDevice(ClientPtr client)
     swaps(&stuff->mask_len);
     swaps(&stuff->num_modifiers);
 
-    mods = (uint32_t *) &stuff[1];
+    mods = (uint32_t *) &stuff[1] + stuff->mask_len;
 
     for (i = 0; i < stuff->num_modifiers; i++, mods++) {
         swapl(mods);
diff --git a/test/xi2/protocol-xipassivegrabdevice.c b/test/xi2/protocol-xipassivegrabdevice.c
index 84b386bf3..dd51757ff 100644
--- a/test/xi2/protocol-xipassivegrabdevice.c
+++ b/test/xi2/protocol-xipassivegrabdevice.c
@@ -137,6 +137,7 @@ request_XIPassiveGrabDevice(ClientPtr client, xXIPassiveGrabDeviceReq * req,
 {
     int rc;
     int modifiers;
+    int mask_len;
 
     rc = ProcXIPassiveGrabDevice(&client_request);
     assert(rc == error);
@@ -153,10 +154,11 @@ request_XIPassiveGrabDevice(ClientPtr client, xXIPassiveGrabDeviceReq * req,
     swaps(&req->deviceid);
     modifiers = req->num_modifiers;
     swaps(&req->num_modifiers);
+    mask_len = req->mask_len;
     swaps(&req->mask_len);
 
     while (modifiers--) {
-        CARD32 *mod = ((CARD32 *) (req + 1)) + modifiers;
+        CARD32 *mod = ((CARD32 *) (req + 1)) + mask_len + modifiers;
 
         swapl(mod);
     }
@@ -228,6 +230,11 @@ test_XIPassiveGrabDevice(void)
     request->detail = XIAnyButton;
     request_XIPassiveGrabDevice(&client_request, request, Success, 0);
 
+    /* Set a few random masks to make sure we handle modifiers correctly */
+    SetBit(mask, XI_ButtonPress);
+    SetBit(mask, XI_KeyPress);
+    SetBit(mask, XI_Enter);
+
     /* some modifiers */
     request->num_modifiers = N_MODS;
     request->length += N_MODS;