[PATCH] present: fix freed pointer access

[Lionel Landwerlin]

I've noticed at least another bug report which seems to abort on 
corrupted memory.
This could be the source of it (I'm still running the Xwayland that 
produced this backtrace... YOLO).

-
Lionel

On 24/08/2018 22:27, Lionel Landwerlin wrote:
> When a vblank has been marked as aborted, it's going to be free in the
> flip_notify function when stopped. We can't notify it after it's
> stopped because the pointer is invalid.
>
> Valgrind backtrace:
>
> ==5331== Invalid read of size 8
> ==5331==    at 0x212B4D: present_vblank_notify (present_vblank.c:34)
> ==5331==    by 0x21439B: present_wnmd_flip_notify (present_wnmd.c:194)
> ==5331==    by 0x21439B: present_wnmd_event_notify (present_wnmd.c:228)
> ==5331==    by 0x156216: xwl_present_sync_callback (xwayland-present.c:282)
> ==5331==    by 0x6570FCD: ffi_call_unix64 (in /usr/lib/x86_64-linux-gnu/libffi.so.6.0.4)
> ==5331==    by 0x657093E: ffi_call (in /usr/lib/x86_64-linux-gnu/libffi.so.6.0.4)
> ==5331==    by 0x4DDB183: ??? (in /usr/lib/x86_64-linux-gnu/libwayland-client.so.0.3.0)
> ==5331==    by 0x4DD79D8: ??? (in /usr/lib/x86_64-linux-gnu/libwayland-client.so.0.3.0)
> ==5331==    by 0x4DD8EA3: wl_display_dispatch_queue_pending (in /usr/lib/x86_64-linux-gnu/libwayland-client.so.0.3.0)
> ==5331==    by 0x14BCCA: xwl_read_events (xwayland.c:814)
> ==5331==    by 0x2AC0D0: ospoll_wait (ospoll.c:651)
> ==5331==    by 0x2A5322: WaitForSomething (WaitFor.c:208)
> ==5331==    by 0x27574B: Dispatch (dispatch.c:421)
> ==5331==  Address 0x1b44dc98 is 40 bytes inside a block of size 184 free'd
> ==5331==    at 0x48369EB: free (vg_replace_malloc.c:530)
> ==5331==    by 0x213B0A: present_wnmd_free_idle_vblanks (present_wnmd.c:118)
> ==5331==    by 0x213B0A: present_wnmd_flips_stop (present_wnmd.c:161)
> ==5331==    by 0x2143EF: present_wnmd_flip_notify (present_wnmd.c:192)
> ==5331==    by 0x2143EF: present_wnmd_event_notify (present_wnmd.c:228)
> ==5331==    by 0x156216: xwl_present_sync_callback (xwayland-present.c:282)
> ==5331==    by 0x6570FCD: ffi_call_unix64 (in /usr/lib/x86_64-linux-gnu/libffi.so.6.0.4)
> ==5331==    by 0x657093E: ffi_call (in /usr/lib/x86_64-linux-gnu/libffi.so.6.0.4)
> ==5331==    by 0x4DDB183: ??? (in /usr/lib/x86_64-linux-gnu/libwayland-client.so.0.3.0)
> ==5331==    by 0x4DD79D8: ??? (in /usr/lib/x86_64-linux-gnu/libwayland-client.so.0.3.0)
> ==5331==    by 0x4DD8EA3: wl_display_dispatch_queue_pending (in /usr/lib/x86_64-linux-gnu/libwayland-client.so.0.3.0)
> ==5331==    by 0x14BCCA: xwl_read_events (xwayland.c:814)
> ==5331==    by 0x2AC0D0: ospoll_wait (ospoll.c:651)
> ==5331==    by 0x2A5322: WaitForSomething (WaitFor.c:208)
> ==5331==  Block was alloc'd at
> ==5331==    at 0x48377D5: calloc (vg_replace_malloc.c:711)
> ==5331==    by 0x212D9F: present_vblank_create (present_vblank.c:69)
> ==5331==    by 0x214014: present_wnmd_pixmap (present_wnmd.c:610)
> ==5331==    by 0x21576C: proc_present_pixmap (present_request.c:150)
> ==5331==    by 0x27599D: Dispatch (dispatch.c:479)
> ==5331==    by 0x279945: dix_main (main.c:276)
> ==5331==    by 0x633AB16: (below main) (libc-start.c:310)
>
> Signed-off-by: Lionel Landwerlin <lionel.g.landwerlin at intel.com>
> Reviewed-by: Daniel Stone <daniels at collabora.com>
> Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=107314
> ---
>   present/present_wnmd.c | 3 ++-
>   1 file changed, 2 insertions(+), 1 deletion(-)
>
> diff --git a/present/present_wnmd.c b/present/present_wnmd.c
> index 80ffb014e..48f66b357 100644
> --- a/present/present_wnmd.c
> +++ b/present/present_wnmd.c
> @@ -190,8 +190,9 @@ present_wnmd_flip_notify(present_vblank_ptr vblank, uint64_t ust, uint64_t crtc_
>   
>       if (vblank->abort_flip)
>           present_wnmd_flips_stop(window);
> +    else
> +        present_vblank_notify(vblank, PresentCompleteKindPixmap, PresentCompleteModeFlip, ust, crtc_msc);
>   
> -    present_vblank_notify(vblank, PresentCompleteKindPixmap, PresentCompleteModeFlip, ust, crtc_msc);
>       present_wnmd_flip_try_ready(window);
>   }
>