Bug#1110980: /var/lock/ is the standard interface for serial devices locks

[Marco d'Itri]

clone 1110980 -1
severity -1 normal
retitle -1 Change the policy for locking serial devices?
reassign -1 debian-policy
thanks

systemd upstream wants /var/lock/ to not be world-writeable for very
good reasons, but FHS, which is referenced by Debian policy, still 
mandates it as the ABI for the lock files of serial devices.
I am opening this bug to explore our options.

For the time being, a good enough compromise for Debian is to have 
/var/lock/ writeable only by group dialout.
But HDB-style serial device locks come from the early '80s, and maybe at 
this point we can agree that just using flock(2) on the serial device is 
a better design.
Indeed, 12 years ago there was an attempt to stop using HDB-style locks 
(see #728023), but it did not lead to a policy change and it was 
obviously not completed since there are still many packages using them.

OTOH a transition would not be totally trivial, because some software 
would need to be patched by their maintainers to implement flock(2) 
locking.

On Aug 13, Marco d'Itri <md at linux.it> wrote:

>Package: systemd
>Version: 258~rc2-2
>Severity: critical
>
>Control: forwarded -1 https://github.com/systemd/systemd/issues/38563
>
>Breaks unrelated software.
>
>/var/lock/ is not just the dumping ground for lock files of random
>applications, but also the published interface for system-wide locks of
>serial devices.
>
>From section 5.9.1 of the FHS:
>
>   Lock files should be stored within the /var/lock directory
>   structure.
>
>   Lock files for devices and other resources shared by multiple
>   applications, such as the serial device lock files that were
>   originally found in either /usr/spool/locks or /usr/spool/uucp,
>   must now be stored in /var/lock. The naming convention which
>   must be used is "LCK.." followed by the base name of the
>   device. For example, to lock /dev/ttyS0 the file "LCK..ttyS0"
>   would be created. ^[43]
>
>I think that this can be easily solved by making /run/lock/ owned by
>group dialout.
>
>-- 
>ciao,
>Marco



-- 
ciao,
Marco
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