linux-kernel - Re: [PATCH] tty: don't crash in tty_init_dev when missing tty

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Message-ID: <CAMuHMdXETD5azNxPgzzhbx_kNh93EN3a8q6FcEVBV=MvLXzYGw@mail.gmail.com>
Date:   Mon, 25 Nov 2019 09:06:24 +0100
From:   Geert Uytterhoeven <geert@...ux-m68k.org>
To:     Jiri Slaby <jslaby@...e.cz>
Cc:     Greg KH <gregkh@...uxfoundation.org>,
        "open list:SERIAL DRIVERS" <linux-serial@...r.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Sudip Mukherjee <sudipm.mukherjee@...il.com>
Subject: Re: [PATCH] tty: don't crash in tty_init_dev when missing tty_port

Hi Jiri,

On Fri, Nov 22, 2019 at 11:20 AM Jiri Slaby <jslaby@...e.cz> wrote:
> We currently warn the user when tty->port is not set in tty_init_dev
> yet. The warning says that the kernel will crash later. And it really
> will only few lines below at:
> tty->port->itty = tty;
>
> So be nice and avoid the crash -- return an error instead. And update
> the warning.

As per Greg's comment on another patch in
https://lore.kernel.org/lkml/20191121135743.GA552517@kroah.com/,
that will still cause systems with panic-on-warn to reboot.

> Signed-off-by: Jiri Slaby <jslaby@...e.cz>
> Cc: Sudip Mukherjee <sudipm.mukherjee@...il.com>
> ---
>  drivers/tty/tty_io.c | 9 ++++++---
>  1 file changed, 6 insertions(+), 3 deletions(-)
>
> diff --git a/drivers/tty/tty_io.c b/drivers/tty/tty_io.c
> index cb6370906a6d..d9f54c7d94f2 100644
> --- a/drivers/tty/tty_io.c
> +++ b/drivers/tty/tty_io.c
> @@ -1345,9 +1345,12 @@ struct tty_struct *tty_init_dev(struct tty_driver *driver, int idx)
>         if (!tty->port)
>                 tty->port = driver->ports[idx];
>
> -       WARN_RATELIMIT(!tty->port,
> -                       "%s: %s driver does not set tty->port. This will crash the kernel later. Fix the driver!\n",
> -                       __func__, tty->driver->name);
> +       if (WARN_RATELIMIT(!tty->port,
> +                       "%s: %s driver does not set tty->port. This would crash the kernel. Fix the driver!\n",
> +                       __func__, tty->driver->name)) {
> +               retval = -EINVAL;
> +               goto err_release_lock;
> +       }
>
>         retval = tty_ldisc_lock(tty, 5 * HZ);
>         if (retval)

Gr{oetje,eeting}s,

                        Geert

-- 
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@...ux-m68k.org

In personal conversations with technical people, I call myself a hacker. But
when I'm talking to journalists I just say "programmer" or something like that.
                                -- Linus Torvalds