Subject: Re: bug#78757: shepherd: dangling file descriptor to /dev/console

From: Ludovic Courtès <[email-masked]>
Date: Mon, 16 Jun 2025 15:35:19 +0200

Hi,

[email-masked] writes:

>> ‘shepherd’ marks all previously-opened FDs as O_CLOEXEC upfront—see
>> ‘mark-as-close-on-exec’ in ‘shepherd.scm’.  Those opened later are
>> opened with O_CLOEXEC, except for user code that explicitly omits the
>> O_CLOEXEC flag.
>
> Hmmm.... I have at one point (before the above (port-for-each ...)
>
> (define *s* (open-output-file "/proc/self/fd/1"))
>
> to have an early log output to (on ordinary PC) /dev/tty1. But maybe /dev/tty1
> is a synonym for /dev/console. Let's test that:
>
> (fileno *s*) returns 19 indeed! Now all I have to do is (fcntl *s*
> F_SETFD FD_CLOEXEC) after creating *s*.

Ah yes, it’s easy to shot oneself in the foot.  ;-)

To reduce the risks, ‘shepherd’ replaces ‘call-with-input-file’ and
‘call-with-output-file’ with O_CLOEXEC variants (commit
47c693d51a991e9a3d5ed6e75760c61e329cc537) because it wouldn’t make much
sense to not have O_CLOEXEC for these.  However, the other procedures
are left unchanged because users might need it.

> So you can close that ticket.

Thanks,
Ludo’.