Re: [PATCH v2 1/2] printk: Check valid console index for preferred console

Tony Lindgren
2023-10-11T16:17:19Z

* Petr Mladek <pmladek@suse.com> [231011 15:26]:
> On Wed 2023-10-11 12:18:03, Tony Lindgren wrote:
> > * Greg Kroah-Hartman <gregkh@linuxfoundation.org> [231011 07:53]:
> > > On Wed, Oct 11, 2023 at 10:43:25AM +0300, Tony Lindgren wrote:
> > > > Let's check for valid console index values to avoid bogus console index
> > > > numbers from kernel command line. While struct console uses short for
> > > > index, and negative index values are used by some device drivers, we do
> > > > not want to allow negative values for preferred console.
> > >
> > > What drivers use a negative index for the console?
> >
> > This is based on grepping with $ git grep "co->index =" drivers/tty/
> >
> > Not sure what all might be stopping making struct console index unsigned.
>
> The value -1 is used for initializing struct console, see:
>
> $> git grep -A10 "struct console.*=" | \
> grep -e "struct console" -e index | \
> grep -B1 index
> [...]
> drivers/tty/serial/8250/8250_core.c:static struct console univ8250_console = {
> drivers/tty/serial/8250/8250_core.c- .index = -1,
> [...]
> drivers/tty/serial/imx.c:static struct console imx_uart_console = {
> drivers/tty/serial/imx.c- .index = -1,
> drivers/tty/serial/ip22zilog.c:static struct console ip22zilog_console = {
> drivers/tty/serial/ip22zilog.c- .index = -1,
> drivers/tty/serial/kgdb_nmi.c:static struct console kgdb_nmi_console = {
> drivers/tty/serial/kgdb_nmi.c- .index = -1,
> drivers/tty/serial/lantiq.c:static struct console lqasc_console = {
> drivers/tty/serial/lantiq.c- .index = -1,
> drivers/tty/serial/liteuart.c:static struct console liteuart_console = {
> drivers/tty/serial/liteuart.c- .index = -1,
> drivers/tty/serial/lpc32xx_hs.c:static struct console lpc32xx_hsuart_console = {
> drivers/tty/serial/lpc32xx_hs.c- .index = -1,
> drivers/tty/serial/ma35d1_serial.c:static struct console ma35d1serial_console = {
> drivers/tty/serial/ma35d1_serial.c- .index = -1,
> drivers/tty/serial/mcf.c:static struct console mcf_console = {
> drivers/tty/serial/mcf.c- .index = -1,
> [...]
>
> It means that the index still has be get assigned. For example, it is
> used here:
>
> static int try_enable_preferred_console(struct console *newcon,
> bool user_specified)
> {
> [...]
> if (newcon->index < 0)
> newcon->index = c->index;
> [...]

OK

> Resume:
>
> 1. We must either keep signed short in struct console or
> use another check for non-yet assigned index.

OK thanks for clarifying the usage for it.

> 2. We should fix the commit message and the comment. We should
> explain that negative value is used in struct console
> to distinguish a non-yet-registered/assigned index/port.

I'll send v3 patches tomorrow with updated commit message and comments.

Thanks,

Tony