[PATCH xserver v2] xwayland: Remove xwl_present_window from privates on cleanup

[Michel Dänzer]

On 2018-09-05 10:35 a.m., Olivier Fourdan wrote:
> Xwayland's `xwl_destroy_window()` invokes `xwl_present_cleanup()`
> before the common `DestroyWindow()`.
> 
> But then `DestroyWindow()` calls `present_destroy_window()` which will
> possibly end up in `xwl_present_abort_vblank()` which will try to access
> data that was previously freed by `xwl_present_cleanup()`:
> 
>   Invalid read of size 8
>      at 0x434184: xwl_present_abort_vblank (xwayland-present.c:378)
>      by 0x53785B: present_wnmd_abort_vblank (present_wnmd.c:651)
>      by 0x53695A: present_free_window_vblank (present_screen.c:87)
>      by 0x53695A: present_destroy_window (present_screen.c:152)
>      by 0x42A90D: xwl_destroy_window (xwayland.c:653)
>      by 0x584298: compDestroyWindow (compwindow.c:613)
>      by 0x53CEE3: damageDestroyWindow (damage.c:1570)
>      by 0x4F1BB8: DbeDestroyWindow (dbe.c:1326)
>      by 0x46F7F6: FreeWindowResources (window.c:1031)
>      by 0x472847: DeleteWindow (window.c:1099)
>      by 0x46B54C: doFreeResource (resource.c:880)
>      by 0x46C706: FreeClientResources (resource.c:1146)
>      by 0x446ADE: CloseDownClient (dispatch.c:3473)
>    Address 0x182abde0 is 80 bytes inside a block of size 112 free'd
>      at 0x4C2FDAC: free (vg_replace_malloc.c:530)
>      by 0x42A937: xwl_destroy_window (xwayland.c:647)
>      by 0x584298: compDestroyWindow (compwindow.c:613)
>      by 0x53CEE3: damageDestroyWindow (damage.c:1570)
>      by 0x4F1BB8: DbeDestroyWindow (dbe.c:1326)
>      by 0x46F7F6: FreeWindowResources (window.c:1031)
>      by 0x472847: DeleteWindow (window.c:1099)
>      by 0x46B54C: doFreeResource (resource.c:880)
>      by 0x46C706: FreeClientResources (resource.c:1146)
>      by 0x446ADE: CloseDownClient (dispatch.c:3473)
>      by 0x446DA5: ProcKillClient (dispatch.c:3279)
>      by 0x4476AF: Dispatch (dispatch.c:479)
>    Block was alloc'd at
>      at 0x4C30B06: calloc (vg_replace_malloc.c:711)
>      by 0x433F46: xwl_present_window_get_priv (xwayland-present.c:54)
>      by 0x434228: xwl_present_get_crtc (xwayland-present.c:302)
>      by 0x539728: proc_present_query_capabilities (present_request.c:227)
>      by 0x4476AF: Dispatch (dispatch.c:479)
>      by 0x44B5B5: dix_main (main.c:276)
>      by 0x75F611A: (below main) (libc-start.c:308)
> 
> This is because `xwl_present_cleanup()` frees the memory but does not
> remove it from the window's privates, and `xwl_present_abort_vblank()`
> will still find it and hence try to access that freed memory...
> 
> Clear `xwl_present_cleanup()` after `DestroyWindow()` so that
> `xwl_present_abort_vblank()` can still access valid memory before it's
> freed.

This last paragraph doesn't seem to match the rest of the patch.


-- 
Earthling Michel Dänzer               |               http://www.amd.com
Libre software enthusiast             |             Mesa and X developer