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Generating the modifier modmap, the helper function generate_modkeymap()
would check the entire range up to the MAP_LENGTH.
However, the given keymap might have less keycodes than MAP_LENGTH, in
which case we would go beyond the size of the modmap, as reported by
ASAN:
==ERROR: AddressSanitizer: heap-buffer-overflow
READ of size 1 at 0x5110001c225b thread T0
#0 0x5e7369393873 in generate_modkeymap ../dix/inpututils.c:309
#1 0x5e736930dcce in ProcGetModifierMapping ../dix/devices.c:1794
#2 0x5e7369336489 in Dispatch ../dix/dispatch.c:550
#3 0x5e736934407d in dix_main ../dix/main.c:275
#5 0x7e46d47b2ecb in __libc_start_main
#6 0x5e73691be324 in _start (xserver/build/hw/xwayland/Xwayland)
Address is located 0 bytes after 219-byte region
allocated by thread T0 here:
#0 0x7e46d4cfc542 in realloc
#1 0x5e73695aa90e in _XkbCopyClientMap ../xkb/xkbUtils.c:1142
#2 0x5e73695aa90e in XkbCopyKeymap ../xkb/xkbUtils.c:1966
#3 0x5e73695b1b2f in XkbDeviceApplyKeymap ../xkb/xkbUtils.c:2023
#4 0x5e73691c6c18 in keyboard_handle_keymap ../hw/xwayland/xwayland-input.c:1194
As MAP_LENGTH is used in various code paths where the max keycode might
not be easily available, best is to always use MAP_LENGTH to allocate the
keymaps so that the code never run past the buffer size.
If the max key code is smaller than the MAP_LENGTH limit, fill-in the gap
with zeros.
That also simplifies the code slightly as we do not constantly need to
reallocate the keymap to adjust to the max key code size.
Closes: https://gitlab.freedesktop.org/xorg/xserver/-/issues/1780
Signed-off-by: Olivier Fourdan <ofourdan@redhat.com>
Part-of: <https://gitlab.freedesktop.org/xorg/xserver/-/merge_requests/1762>
(cherry picked from commit 92bcebfd7e)
The X server uses this directory to store the compiled version of the
current keymap and/or any scratch keymaps used by clients. The X server
or some other tool might destroy or replace the files in this directory,
so it is not a safe place to store compiled keymaps for long periods of
time. The default keymap for any server is usually stored in:
X<num>-default.xkm
where <num> is the display number of the server in question, which makes
it possible for several servers *on the same host* to share the same
directory.
Unless the X server is modified, sharing this directory between servers on
different hosts could cause problems.