[PATCH] tty: vt: keyboard: reject invalid keycodes

From: Dmitry Torokhov
Date: Fri Nov 22 2019 - 15:42:26 EST

Do not try to handle keycodes that are too big, otherwise we risk doing
out-of-bounds writes:

BUG: KASAN: global-out-of-bounds in clear_bit include/asm-generic/bitops-instrumented.h:56 [inline]
BUG: KASAN: global-out-of-bounds in kbd_keycode drivers/tty/vt/keyboard.c:1411 [inline]
BUG: KASAN: global-out-of-bounds in kbd_event+0xe6b/0x3790 drivers/tty/vt/keyboard.c:1495
Write of size 8 at addr ffffffff89a1b2d8 by task syz-executor108/1722
kbd_keycode drivers/tty/vt/keyboard.c:1411 [inline]
kbd_event+0xe6b/0x3790 drivers/tty/vt/keyboard.c:1495
input_to_handler+0x3b6/0x4c0 drivers/input/input.c:118
input_pass_values.part.0+0x2e3/0x720 drivers/input/input.c:145
input_pass_values drivers/input/input.c:949 [inline]
input_set_keycode+0x290/0x320 drivers/input/input.c:954
evdev_handle_set_keycode_v2+0xc4/0x120 drivers/input/evdev.c:882
evdev_do_ioctl drivers/input/evdev.c:1150 [inline]

In this case we were dealing with a fuzzed HID device that declared over
12K buttons, and while HID layer should not be reporting to us such big
keycodes, we should also be defensive and reject invalid data ourselves as

Reported-by: syzbot+19340dff067c2d3835c0@xxxxxxxxxxxxxxxxxxxxxxxxx
Signed-off-by: Dmitry Torokhov <dmitry.torokhov@xxxxxxxxx>
drivers/tty/vt/keyboard.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/tty/vt/keyboard.c b/drivers/tty/vt/keyboard.c
index 515fc095e3b4..15d33fa0c925 100644
--- a/drivers/tty/vt/keyboard.c
+++ b/drivers/tty/vt/keyboard.c
@@ -1491,7 +1491,7 @@ static void kbd_event(struct input_handle *handle, unsigned int event_type,

if (event_type == EV_MSC && event_code == MSC_RAW && HW_RAW(handle->dev))
- if (event_type == EV_KEY)
+ if (event_type == EV_KEY && event_code <= KEY_MAX)
kbd_keycode(event_code, value, HW_RAW(handle->dev));