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Simon Ser 7915a2ff59 tinywl: fix wlr_seat use-after-free on exit 
When pressing the keybinding to shut down the compositor, the following
use-after-free is triggered:

    ==1165966==ERROR: AddressSanitizer: heap-use-after-free on address 0x51800000ade0 at pc 0x7fa6728b4531 bp 0x7ffe540a6aa0 sp 0x7ffe540a6a90
    READ of size 8 at 0x51800000ade0 thread T0
        #0 0x7fa6728b4530 in wlr_seat_set_keyboard ../types/seat/wlr_seat_keyboard.c:124
        #1 0x58a83fa7fd4e in keyboard_handle_key ../tinywl/tinywl.c:228
        #2 0x7fa673a1901d in wl_signal_emit_mutable (/usr/lib/libwayland-server.so.0+0xa01d) (BuildId: d943a6a6069d1b5293dad7c842d26ce407ebdd19)
        #3 0x7fa67295b4be in wlr_keyboard_notify_key ../types/wlr_keyboard.c:102
        #4 0x7fa67295c791 in wlr_keyboard_finish ../types/wlr_keyboard.c:165
        #5 0x7fa672848cb1 in destroy_wl_seat ../backend/wayland/seat.c:293
        #6 0x7fa672833dca in backend_destroy ../backend/wayland/backend.c:493
        #7 0x7fa6727b49e8 in wlr_backend_destroy ../backend/backend.c:67
        #8 0x7fa67282d334 in multi_backend_destroy ../backend/multi/backend.c:59
        #9 0x7fa67282da5a in handle_event_loop_destroy ../backend/multi/backend.c:110
        #10 0x7fa673a18b98 in wl_event_loop_destroy (/usr/lib/libwayland-server.so.0+0x9b98) (BuildId: d943a6a6069d1b5293dad7c842d26ce407ebdd19)
        #11 0x7fa673a1b43c in wl_display_destroy (/usr/lib/libwayland-server.so.0+0xc43c) (BuildId: d943a6a6069d1b5293dad7c842d26ce407ebdd19)
        #12 0x58a83fa8ada1 in main ../tinywl/tinywl.c:1068
        #13 0x7fa672043ccf  (/usr/lib/libc.so.6+0x25ccf) (BuildId: c0caa0b7709d3369ee575fcd7d7d0b0fc48733af)
        #14 0x7fa672043d89 in __libc_start_main (/usr/lib/libc.so.6+0x25d89) (BuildId: c0caa0b7709d3369ee575fcd7d7d0b0fc48733af)
        #15 0x58a83fa7e7c4 in _start (/home/simon/src/wlroots/build/tinywl/tinywl+0x167c4) (BuildId: 1febf2a5a18bda0f6b67377a132484061875e248)

    0x51800000ade0 is located 352 bytes inside of 880-byte region [0x51800000ac80,0x51800000aff0)
    freed by thread T0 here:
        #0 0x7fa6732dfdb2 in __interceptor_free /usr/src/debug/gcc/gcc/libsanitizer/asan/asan_malloc_linux.cpp:52
        #1 0x7fa6728c6a1e in wlr_seat_destroy ../types/seat/wlr_seat.c:245
        #2 0x7fa6728c6a7a in handle_display_destroy ../types/seat/wlr_seat.c:251
        #3 0x7fa673a1b3c6 in wl_display_destroy (/usr/lib/libwayland-server.so.0+0xc3c6) (BuildId: d943a6a6069d1b5293dad7c842d26ce407ebdd19)

    previously allocated by thread T0 here:
        #0 0x7fa6732e0cc1 in __interceptor_calloc /usr/src/debug/gcc/gcc/libsanitizer/asan/asan_malloc_linux.cpp:77
        #1 0x7fa6728c6a9d in wlr_seat_create ../types/seat/wlr_seat.c:255
        #2 0x58a83fa8a8d3 in main ../tinywl/tinywl.c:1024
        #3 0x7fa672043ccf  (/usr/lib/libc.so.6+0x25ccf) (BuildId: c0caa0b7709d3369ee575fcd7d7d0b0fc48733af)

This happens because the wlr_seat is destroyed before the
wlr_keyboard. Destroying the wlr_keyboard has the side effect of
implicitly releasing keys currently held down.

Explicitly destroying the wlr_backend before the wl_display fixes
this.

Suggested-by: Isaac Freund <ifreund@ifreund.xyz>
2024-03-04 12:50:14 +00:00
..
.gitignore Tiny Wayland compositor 2018-08-15 18:27:48 -04:00
LICENSE CC0 2018-08-15 19:17:20 -04:00
Makefile build: bump version to 0.18.0-dev 2023-11-21 17:28:06 +01:00
meson.build tinywl: depend on the server xdg-shell header 2024-01-09 21:39:02 +03:00
README.md tinywl: remove outdated non-feature from README.md 2022-04-01 14:22:28 +00:00
tinywl.c tinywl: fix wlr_seat use-after-free on exit 2024-03-04 12:50:14 +00:00

README.md

TinyWL

This is the "minimum viable product" Wayland compositor based on wlroots. It aims to implement a Wayland compositor in the fewest lines of code possible, while still supporting a reasonable set of features. Reading this code is the best starting point for anyone looking to build their own Wayland compositor based on wlroots.

Building TinyWL

TinyWL is disconnected from the main wlroots build system, in order to make it easier to understand the build requirements for your own Wayland compositors. Simply install the dependencies:

  • wlroots
  • wayland-protocols

And run make.

Running TinyWL

You can run TinyWL with ./tinywl. In an existing Wayland or X11 session, tinywl will open a Wayland or X11 window respectively to act as a virtual display. You can then open Wayland windows by setting WAYLAND_DISPLAY to the value shown in the logs. You can also run ./tinywl from a TTY.

In either case, you will likely want to specify -s [cmd] to run a command at startup, such as a terminal emulator. This will be necessary to start any new programs from within the compositor, as TinyWL does not support any custom keybindings. TinyWL supports the following keybindings:

  • Alt+Escape: Terminate the compositor
  • Alt+F1: Cycle between windows

Limitations

Notable omissions from TinyWL:

  • HiDPI support
  • Any kind of configuration, e.g. output layout
  • Any protocol other than xdg-shell (e.g. layer-shell, for panels/taskbars/etc; or Xwayland, for proxied X11 windows)
  • Optional protocols, e.g. screen capture, primary selection, virtual keyboard, etc. Most of these are plug-and-play with wlroots, but they're omitted for brevity.