Re: [PATCH] vt: keyboard: add NULL check for vc_cons[fg_console].d in kbd_keycode and kbd_rawcode

Greg Kroah-Hartman
2026-03-12T14:22:13Z

On Sat, Feb 07, 2026 at 07:31:12PM -0500, Daniel Hodges wrote:
> kbd_keycode() and kbd_rawcode() dereference vc_cons[fg_console].d
> without checking if it is NULL. The foreground console should normally
> always be allocated, but there could be a time during console setup or
> teardown where this pointer could be NULL, leading to a general
> protection fault.
>
> Syzkaller triggers this by injecting USB HID input events that reach
> kbd_event() while the console state may not be fully consistent. The crash
> manifests as a null-ptr-deref in __queue_work when put_queue() or
> puts_queue() calls tty_flip_buffer_push() on the uninitialized vc port.
>
> Add a NULL check for vc at the start of both kbd_rawcode() and
> kbd_keycode() to bail out early if the foreground console is not allocated.
>
> Reported-by: syzbot+c3693b491545af43db87@syzkaller.appspotmail.com
> Closes: https://syzkaller.appspot.com/bug?extid=c3693b491545af43db87
> Reported-by: syzbot+03f79366754268a0f20c@syzkaller.appspotmail.com
> Closes: https://syzkaller.appspot.com/bug?extid=03f79366754268a0f20c
> Fixes: 1da177e4c3f4 ("Linux-2.6.12-rc2")
> Signed-off-by: Daniel Hodges <git@danielhodges.dev>
> ---
> drivers/tty/vt/keyboard.c | 6 ++++++
> 1 file changed, 6 insertions(+)
>
> diff --git a/drivers/tty/vt/keyboard.c b/drivers/tty/vt/keyboard.c
> index a2116e135a82..975830013d24 100644
> --- a/drivers/tty/vt/keyboard.c
> +++ b/drivers/tty/vt/keyboard.c
> @@ -1389,6 +1389,9 @@ static void kbd_rawcode(unsigned char data)
> {
> struct vc_data *vc = vc_cons[fg_console].d;
>
> + if (!vc)
> + return;
> +

What prevents vc from being NULL right after checking this?

> kbd = &kbd_table[vc->vc_num];
> if (kbd->kbdmode == VC_RAW)
> put_queue(vc, data);
> @@ -1405,6 +1408,9 @@ static void kbd_keycode(unsigned int keycode, int down, bool hw_raw)
> struct keyboard_notifier_param param = { .vc = vc, .value = keycode, .down = down };
> int rc;
>
> + if (!vc)
> + return;

Same here, where is the locking?

thanks,

greg k-h