With SD_VARLINK_SERVER_ROOT_ONLY, we refuse all unprivileged operations.
This is silly, the user can and should be able to do anything that doesn't
require privileges.
E.g.:
$ SYSTEMD_LOG_LEVEL=debug varlinkctl introspect /usr/lib/systemd/systemd-pcrextend
Forking off Varlink child process '/usr/lib/systemd/systemd-pcrextend'.
Successfully forked off '(sd-vlexec)' as PID 568993.
varlink: Setting state idle-client
json-stream: Sending message: {"method":"org.varlink.service.GetInterfaceDescription","parameters":{"interface":"io.systemd.PCRExtend"}}
Skipping PR_SET_MM, as we don't have privileges.
varlink: Changing state idle-client → calling
varlink: Unprivileged client attempted connection, refusing.
Failed to run Varlink event loop: Operation not permitted
json-stream: Got POLLHUP from socket.
varlink: Changing state calling → pending-disconnect
varlink: Connection was closed.
Failed to issue org.varlink.service.GetInterfaceDescription() varlink call: Connection reset by peer
This and similar commands now work, e.g.
$ SYSTEMD_LOG_LEVEL=debug varlinkctl call --more ./build/bootctl io.systemd.BootControl.ListBootEntries {}
...
Failed to open directory "/efi": No such file or directory
File system "/boot" is not a FAT EFI System Partition (ESP) file system.
...
Method call failed: Permission denied
{
"origin" : "linux",
"errno" : 13,
"errnoName" : "EACCES"
}
Which is fine — we lack privileges to actually return a useful answer, but the
call itself should go through.
I didn't touch udevd, which refuses to run if it is not root, and does a lot of
privileged setup, so would refuse to start even if the check was removed.
I am really not a fan of full code lines passed to macros as parameters.
Let's get rid of the 3rd parameter of FOREACH_OPTION() hence:
1. Let's return errors just as a regular value (though a negative one),
that can be handled via a OPTION_ERROR case statement for the switch.
This normalizes handling of the error, just like any other event
returned by the option parser.
2. In order to avoid exploding the amount of boilerplate in each use
(that just propagates the error on OPTION_ERROR), let's then
introduce an explicit FOREACH_OPTION_OR_RETURN(), that returns from
the calling function on its own (and makes that clear in the name).
Together this cleans up, normalizes the logic and shortens the code.
It was requested to make the 'c', 'opt', and 'arg' params the same, i.e.
defined through the FOREACH_OPTION macro. But we can't do that easily,
because 'c' was defined in the for loop definition, and we can only
define variables of the same type in that way. Also, in some cases we
need only 'c', in other cases with need 'c' and 'arg, in some cases 'c'
and 'opt', and in other cases all three. We'd need to either
conditionalize or mark those variables with _unused_ to deal with
compiler warnings. But a different approach works quite nicely: add
state.opt and state.arg to show the current option and it's argument.
(The short names are picked on purpose to reduce verbosity since those
are used a lot.)
```
$ build/systemd-mute-console -q
Code should not be reached at src/mute-console/mute-console.c:103, function parse_argv(). Aborting. 💥
Aborted (core dumped)
```
For "wizard" style interactive tools it's very annoying if they are
interrupted by kernel log output or PID1's status output. let's add some
infra to disable this temporarily. I decided to implement this as an IPC
service so that we can make this robust: if the client request the
muting dies we can automatically unmute again.
This is hence a tiny varlink service, but it can also be started
directly from the cmdline.
Zbigniew Jędrzejewski-Szmek
Lennart Poettering
Mike Yuan
Antonio Alvarez Feijoo
Lennart Poettering