• Lyude Paul's avatar
    xwayland: Store xwl_tablet_pad in its own private key · ba0e789b
    Lyude Paul authored
    When a slave device causes the master virtual pointer device to change
    device types, the device's private data pointer
    (device->public.devicePrivate) is also changed to match the type of the
    slave device. This can be a problem though, as tablet pad devices will
    set the device's private data pointer to their own xwl_tablet_pad
    struct. This can cause us to dereference the pointer as the wrong type,
    and result in a segfault:
    Thread 1 "Xwayland" received signal SIGSEGV, Segmentation fault.
    wl_proxy_marshal (proxy=0x51, opcode=opcode@entry=0) at src/wayland-client.c:792
    792             va_start(ap, opcode);
    (gdb) bt
    0  wl_proxy_marshal (proxy=0x51, opcode=opcode@entry=0) at
    1  0x00005610b27b6c55 in wl_pointer_set_cursor (hotspot_y=0,
      hotspot_x=0, surface=0x0, serial=<optimized out>, wl_pointer=<optimized
      out>) at /usr/include/wayland-client-protocol.h:4610
    2  xwl_seat_set_cursor (xwl_seat=xwl_seat@entry=0x5610b46d5d10) at
    3  0x00005610b27b6ecd in xwl_set_cursor (device=<optimized out>,
      screen=<optimized out>, cursor=<optimized out>, x=<optimized out>,
      y=<optimized out>) at xwayland-cursor.c:249
    4  0x00005610b2800b46 in miPointerUpdateSprite (pDev=0x5610b4501a30) at
    5  miPointerUpdateSprite (pDev=0x5610b4501a30) at mipointer.c:410
    6  0x00005610b2800e56 in miPointerDisplayCursor (pCursor=0x5610b4b35740,
      pScreen=0x5610b3d54410, pDev=0x5610b4501a30) at mipointer.c:206
    7  miPointerDisplayCursor (pDev=0x5610b4501a30, pScreen=0x5610b3d54410,
      pCursor=0x5610b4b35740) at mipointer.c:194
    8  0x00005610b27ed62b in CursorDisplayCursor (pDev=<optimized out>,
      pScreen=0x5610b3d54410, pCursor=0x5610b4b35740) at cursor.c:168
    9  0x00005610b28773ee in AnimCurDisplayCursor (pDev=0x5610b4501a30,
      pScreen=0x5610b3d54410, pCursor=0x5610b4b35740) at animcur.c:197
    10 0x00005610b28eb4ca in ChangeToCursor (pDev=0x5610b4501a30,
      cursor=0x5610b4b35740) at events.c:938
    11 0x00005610b28ec99f in WindowHasNewCursor
      (pWin=pWin@entry=0x5610b4b2e0c0) at events.c:3362
    12 0x00005610b291102d in ChangeWindowAttributes (pWin=0x5610b4b2e0c0,
      vmask=<optimized out>, vlist=vlist@entry=0x5610b4c41dcc,
      client=client@entry=0x5610b4b2c900) at window.c:1561
    13 0x00005610b28db8e3 in ProcChangeWindowAttributes (client=0x5610b4b2c900)
      at dispatch.c:746
    14 0x00005610b28e1e5b in Dispatch () at dispatch.c:497
    15 0x00005610b28e5f34 in dix_main (argc=16, argv=0x7ffc7a601b68,
      envp=<optimized out>) at main.c:276
    16 0x00007f8828cde042 in __libc_start_main (main=0x5610b27ae930 <main>,
      argc=16, argv=0x7ffc7a601b68, init=<optimized out>, fini=<optimized
      out>, rtld_fini=<optimized out>, stack_end=0x7ffc7a601b58) at
    17 0x00005610b27ae96e in _start () at cursor.c:1064
    Simple reproducer in gnome-shell: open up an Xwayland window, press some
    tablet buttons, lock and unlock the screen. Repeat if it doesn't crash
    the first time.
    So, let's fix this by registering our own device-specific private key
    for storing a backpointer to xwl_tablet_pad, so that all input devices
    have their private data pointers set to their respective xwl_seat.
    Reviewed-by: Peter Hutterer's avatarPeter Hutterer <peter.hutterer@who-t.net>
    Signed-off-by: Lyude Paul's avatarLyude Paul <lyude@redhat.com>