[PATCH] tty: don't crash in tty_init_dev when missing tty_port

[PATCH] tty: don't crash in tty_init_dev when missing tty_port

[Jiri Slaby]

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.

Signed-off-by: Jiri Slaby <jslaby@suse.cz>
Cc: Sudip Mukherjee <sudipm.mukherjee@gmail.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)
-- 
2.24.0

Re: [PATCH] tty: don't crash in tty_init_dev when missing tty_port

[Geert Uytterhoeven]

Hi Jiri,

On Fri, Nov 22, 2019 at 11:20 AM Jiri Slaby <jslaby@suse.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@suse.cz>
> Cc: Sudip Mukherjee <sudipm.mukherjee@gmail.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@linux-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