[PATCH xserver v3] xwayland: Remove xwl_present_window from privates on cleanup

[Lionel Landwerlin]

On 05/09/2018 09:49, 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...
>
> Remove `xwl_present_window` from window's privates on cleanup so that no
> other function can find and reuse that data once it's freed.
>
> Bugzilla: https://bugzilla.redhat.com/show_bug.cgi?id=1616269


We also have this fdo bug : 
https://bugs.freedesktop.org/show_bug.cgi?id=107314


> Signed-off-by: Olivier Fourdan <ofourdan at redhat.com>
> ---
>   v2: Remove leftovers from broken initial patch...
>   v3: Rephrase non-sensical explanation of the fix
>
>   hw/xwayland/xwayland-present.c | 5 +++++
>   1 file changed, 5 insertions(+)
>
> diff --git a/hw/xwayland/xwayland-present.c b/hw/xwayland/xwayland-present.c
> index 81e0eb9ce..316e04443 100644
> --- a/hw/xwayland/xwayland-present.c
> +++ b/hw/xwayland/xwayland-present.c
> @@ -147,6 +147,11 @@ xwl_present_cleanup(WindowPtr window)
>       /* Clear timer */
>       xwl_present_free_timer(xwl_present_window);
>   
> +    /* Remove from privates so we don't try to access it later */
> +    dixSetPrivate(&window->devPrivates,
> +                  &xwl_present_window_private_key,
> +                  NULL);
> +
>       free(xwl_present_window);
>   }
>