Re: [PATCH 1/1] tty: fix out-of-bounds access in tty_driver_lookup_tty()

Sven Schnelle
2022-12-09T08:10:48Z

Jiri Slaby <jirislaby@kernel.org> writes:

> On 07. 12. 22, 8:52, Sven Schnelle wrote:
>> When specifying an invalid console= device like console=tty3270,
>> tty_driver_lookup_tty() returns the tty struct without checking
>> whether index is a valid number.
>> [..]
>
> Reviewed-by: Jiri Slaby <jirislaby@kernel.org>
>
> Yes, this makes sense as a sanity check for all drivers. But I would
> _also_ disallow registering such a console in vt:
> --- a/drivers/tty/vt/vt.c
> +++ b/drivers/tty/vt/vt.c
> @@ -3075,6 +3075,11 @@ int vt_kmsg_redirect(int new)
> * The console must be locked when we get here.
> */
>
> +static int vt_console_setup(struct console *co, char *options)
> +{
> + return co->index >= MAX_NR_CONSOLES ? -EINVAL : 0;
> +}
> +
> static void vt_console_print(struct console *co, const char *b,
> unsigned count)
> {
> struct vc_data *vc = vc_cons[fg_console].d;
> @@ -3158,6 +3163,7 @@ static struct tty_driver
> *vt_console_device(struct console *c, int *index)
>
> static struct console vt_console_driver = {
> .name = "tty",
> + .setup = vt_console_setup,
> .write = vt_console_print,
> .device = vt_console_device,
> .unblank = unblank_screen,
>
> That means dmesg would say:
> Console: colour dummy device 80x25
> printk: console [ttyS0] enabled
>
> And not:
> Console: colour dummy device 80x25
> printk: console [tty3270] enabled
> printk: console [ttyS0] enabled

Makes sense. Should i add that to my patch, add a second patch, or
will you submit that?

Thanks
Sven