present: Fix use-after-free in present_create_notifies()

Using the Present extension, if an error occurs while processing and
adding the notifications after presenting a pixmap, the function
present_create_notifies() will clean up and remove the notifications
it added.

However, there are two different code paths that can lead to an error
creating the notify, one being before the notify is being added to the
list, and another one after the notify is added.

When the error occurs before it's been added, it removes the elements up
to the last added element, instead of the actual number of elements
which were added.

As a result, in case of error, as with an invalid window for example, it
leaves a dangling pointer to the last element, leading to a use after
free case later:

 |  Invalid write of size 8
 |     at 0x5361D5: present_clear_window_notifies (present_notify.c:42)
 |     by 0x534A56: present_destroy_window (present_screen.c:107)
 |     by 0x41E441: xwl_destroy_window (xwayland-window.c:1959)
 |     by 0x4F9EC9: compDestroyWindow (compwindow.c:622)
 |     by 0x51EAC4: damageDestroyWindow (damage.c:1592)
 |     by 0x4FDC29: DbeDestroyWindow (dbe.c:1291)
 |     by 0x4EAC55: FreeWindowResources (window.c:1023)
 |     by 0x4EAF59: DeleteWindow (window.c:1091)
 |     by 0x4DE59A: doFreeResource (resource.c:890)
 |     by 0x4DEFB2: FreeClientResources (resource.c:1156)
 |     by 0x4A9AFB: CloseDownClient (dispatch.c:3567)
 |     by 0x5DCC78: ClientReady (connection.c:603)
 |   Address 0x16126200 is 16 bytes inside a block of size 2,048 free'd
 |     at 0x4841E43: free (vg_replace_malloc.c:989)
 |     by 0x5363DD: present_destroy_notifies (present_notify.c:111)
 |     by 0x53638D: present_create_notifies (present_notify.c:100)
 |     by 0x5368E9: proc_present_pixmap_common (present_request.c:164)
 |     by 0x536A7D: proc_present_pixmap (present_request.c:189)
 |     by 0x536FA9: proc_present_dispatch (present_request.c:337)
 |     by 0x4A1E4E: Dispatch (dispatch.c:561)
 |     by 0x4B00F1: dix_main (main.c:284)
 |     by 0x42879D: main (stubmain.c:34)
 |   Block was alloc'd at
 |     at 0x48463F3: calloc (vg_replace_malloc.c:1675)
 |     by 0x5362A1: present_create_notifies (present_notify.c:81)
 |     by 0x5368E9: proc_present_pixmap_common (present_request.c:164)
 |     by 0x536A7D: proc_present_pixmap (present_request.c:189)
 |     by 0x536FA9: proc_present_dispatch (present_request.c:337)
 |     by 0x4A1E4E: Dispatch (dispatch.c:561)
 |     by 0x4B00F1: dix_main (main.c:284)
 |     by 0x42879D: main (stubmain.c:34)

To fix the issue, count and remove the actual number of notify elements
added in case of error.

CVE-2025-62229, ZDI-CAN-27238

This vulnerability was discovered by:
Jan-Niklas Sohn working with Trend Micro Zero Day Initiative

Signed-off-by: Olivier Fourdan <ofourdan@redhat.com>
(cherry picked from commit 5a4286b13f)

Part-of: <https://gitlab.freedesktop.org/xorg/xserver/-/merge_requests/2087>

present/present_notify.c

@@ -90,7 +90,7 @@ present_create_notifies(ClientPtr client, int num_notifies, xPresentNotify *x_no
         if (status != Success)
             goto bail;
 
-        added = i;
+        added++;
     }
     return Success;