On Sat, Nov 30, 2013 at 04:36:18PM -0600, Nathan Whitehorn wrote:
> This took much longer than I'd anticipated, but the patch to init is
> attached. I chose not to make the changes to init rather than
> getttyent() and friends in libc, which I am open to revisiting.

lib/libpam/modules/pam_securetty/pam_securetty.c calls getttynam(3) and
will not allow root login on a "fake" TTY that getttynam() does not
know. This module is enabled by default for the "login" service.

So it is probably better to patch libc rather than init.

> The behavior changes are as follows:

> If the "console" device in /etc/ttys in marked "on", instead of opening
> /dev/console, init will loop through the active kernel console devices,
> and for each will:
> 1. If the kernel console device is in /etc/ttys and marked "on", it
> already has a terminal and will be ignored.
> 2. If marked "off", that is an explicit statement that a console is not
> wanted and so it will be ignored.
> 3. If not present in /etc/ttys, init will run getty with whatever
> parameters "console" has.

This seems to make sense.

> (3) is the main behavioral change. No changes in behavior will occur if
> /etc/ttys is not modified. If we turn on "console" by default, it will
> usually have no effect instead of trying to run multiple gettys, which
> is new. If we then also comment out the ttyu0 line, instead of marking
> it "off", the result will be the conditional presence of a login prompt
> on the first serial port depending on whether it is an active console
> device for the kernel. I believe this is the behavior we are going for.

The terminal type for the console entry should probably be changed to
something other than "unknown" to reduce annoyance.

> Comments and test results would be appreciated.

As a preparatory patch, you could remove se_index and session_index from
init. They are only used to warn about a changed slot number in utmp(5)
which is irrelevant with utmpx. This noise warning would also appear
in most cases when changing from a "fake" console entry to a real line
in /etc/ttys. Also, if you do decide to fake ttys entries in init rather
than libc, the patch to init will be simpler.

Jilles Tjoelker
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