linux-kernel - Re: [PATCH v6 3/3] tty: Change order of ttynull to be linked sooner if enabled as a console.

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <CAHp75VftQASqajiG_z-==CmVMu5Orv_Q8QMj-7W=sxsJPq6bJw@mail.gmail.com>
Date: Tue, 4 Mar 2025 08:51:52 +0200
From: Andy Shevchenko <andy.shevchenko@...il.com>
To: adamsimonelli@...il.com
Cc: linux-serial@...r.kernel.org, linux-kernel@...r.kernel.org, 
	Jiri Slaby <jirislaby@...nel.org>, Greg Kroah-Hartman <gregkh@...uxfoundation.org>, 
	Steven Rostedt <rostedt@...dmis.org>, John Ogness <john.ogness@...utronix.de>, 
	Sergey Senozhatsky <senozhatsky@...omium.org>, Petr Mladek <pmladek@...e.com>
Subject: Re: [PATCH v6 3/3] tty: Change order of ttynull to be linked sooner
 if enabled as a console.

On Tue, Mar 4, 2025 at 5:55 AM <adamsimonelli@...il.com> wrote:
>
> From: Adam Simonelli <adamsimonelli@...il.com>
>
> If CONFIG_NULL_TTY_DEFAULT_CONSOLE is enabled, and CONFIG_VT is disabled,
> ttynull will become the default primary console device, based on the link
> order.
>
> Many distributions ship with CONFIG_VT enabled. On tested desktop hardware
> if CONFIG_VT is disabled, the default console device falls back to
> /dev/ttyS0 instead of /dev/tty.
>
> This could cause issues in user space, and hardware problems:
>
> 1. The user space issues include the case where  /dev/ttyS0 is
> disconnected, and the TCGETS ioctl, which some user space libraries use
> as a probe to determine if a file is a tty, is called on /dev/console and
> fails. Programs that call isatty() on /dev/console and get an incorrect
> false value may skip expected logging to /dev/console

Missing period at the end.

> 2. The hardware issues include the case if a user has a science instrument
> or other device connected to the /dev/ttyS0 port, and they were to upgrade
> to a kernel that is disabling the CONFIG_VT option, kernel logs will then be
> sent to the device connected to /dev/ttyS0 unless they edit their kernel
> command line manually.
>
> The new CONFIG_NULL_TTY_CONSOLE option will give users and distribution
> maintainers an option to avoid this. Disabling CONFIG_VT and enabling
> CONFIG_NULL_TTY_CONSOLE will ensure the default kernel console behavior
> is not dependant on hardware configuration by default, and avoid
> unexpected new behavior on devices connected to the /dev/ttyS0 serial
> port.

...

>  obj-y                          += vt/

+ blank line.

> +# If ttynull is configured to be a console by default, ensure that it is linked
> +# earlier before a real one is selected.
> +obj-$(CONFIG_NULL_TTY_DEFAULT_CONSOLE) \
> +                               += ttynull.o

Here is the question: are you sure that all console drivers that exist
in the kernel happen to be here? Have you grepped the source tree for
checking this?

...

> +# If ttynull is enabled, but not as a boot console, it is linked and used later
> +# after the real ones.
> +ifneq ($(CONFIG_NULL_TTY_DEFAULT_CONSOLE),y)

Also can be written as
ifeq ($(...),)
but it might be less explicit. Up to you.

>  obj-$(CONFIG_NULL_TTY)         += ttynull.o
> +endif

-- 
With Best Regards,
Andy Shevchenko