Fixes use-after-free on exit of labwc running nested:
==50906== Invalid write of size 8
==50906== at 0x4A85403: wl_list_remove (wayland-util.c:57)
==50906== by 0x40BBAF9: destroy_wl_buffer (output.c:146)
==50906== by 0x40B9B4F: backend_destroy (backend.c:488)
==50906== by 0x409E96F: wlr_backend_destroy (backend.c:68)
==50906== by 0x40B78A6: multi_backend_destroy (backend.c:62)
==50906== by 0x409E96F: wlr_backend_destroy (backend.c:68)
==50906== by 0x4043DA0: server_finish (server.c:788)
==50906== by 0x403AA85: main (main.c:277)
==50906== Address 0xb4435e8 is 40 bytes inside a block of size 136 free'd
==50906== at 0x4A3E8EF: free (vg_replace_malloc.c:989)
==50906== by 0x409C954: buffer_destroy (shm.c:28)
==50906== by 0x40E96F4: buffer_consider_destroy (buffer.c:42)
==50906== by 0x40E9754: wlr_buffer_drop (buffer.c:52)
==50906== by 0x41498DA: slot_reset (swapchain.c:44)
==50906== by 0x4149933: wlr_swapchain_destroy (swapchain.c:53)
==50906== by 0x40CB1FA: wlr_output_finish (output.c:410)
==50906== by 0x40BE00B: output_destroy (output.c:957)
==50906== by 0x40CB2FC: wlr_output_destroy (output.c:436)
==50906== by 0x40B9AFC: backend_destroy (backend.c:481)
==50906== by 0x409E96F: wlr_backend_destroy (backend.c:68)
==50906== by 0x40B78A6: multi_backend_destroy (backend.c:62)
==50906== Block was alloc'd at
==50906== at 0x4A42C13: calloc (vg_replace_malloc.c:1675)
==50906== by 0x409CA84: allocator_create_buffer (shm.c:68)
==50906== by 0x409C7BA: wlr_allocator_create_buffer (allocator.c:186)
==50906== by 0x4149B80: wlr_swapchain_acquire (swapchain.c:102)
==50906== by 0x40C90DA: render_cursor_buffer (cursor.c:246)
==50906== by 0x40C93DC: output_cursor_attempt_hardware (cursor.c:303)
==50906== by 0x40C9A61: output_cursor_set_texture (cursor.c:420)
==50906== by 0x40C9738: wlr_output_cursor_set_buffer (cursor.c:352)
==50906== by 0x40F13A0: output_cursor_set_xcursor_image (wlr_cursor.c:507)
==50906== by 0x40F1B28: cursor_output_cursor_update (wlr_cursor.c:630)
==50906== by 0x40F1C2A: cursor_update_outputs (wlr_cursor.c:657)
==50906== by 0x40F1CF9: wlr_cursor_set_xcursor (wlr_cursor.c:674)
Fixes: 7963ba6a0d
("buffer: introduce wlr_buffer_finish()")
udmabuf can create a DMA-BUF backed by a memfd. This is useful
when running with a software implementation of GL/Vulkan: the memfd
can be passed to the parent compositor via wl_shm and the DMA-BUF
can be imported via the usual APIs into GL/Vulkan.
