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nixos/rtkit: Disable debug logging and fix sd_notify #180102

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nixos/rtkit: Disable debug logging and fix sd_notify #180102

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17 changes: 17 additions & 0 deletions nixos/modules/security/rtkit.nix
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Original file line number Diff line number Diff line change
Expand Up @@ -32,6 +32,23 @@ with lib;

systemd.packages = [ pkgs.rtkit ];

# Stop spamming the log and fix sd_notify().
# This bind-mounts the notify socket so the `Status` line
# in `systemctl status` work which makes the constant debug
# logging redundant.
# See also:
# - https://github.com/heftig/rtkit/issues/22
# - https://github.com/heftig/rtkit/issues/27
systemd.services.rtkit-daemon = {
environment.NOTIFY_SOCKET = "/fs/sd-notify";
serviceConfig = {
BindPaths = "/run/systemd/notify:/proc/fs/sd-notify";
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@viraptor viraptor Jul 4, 2022 •
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This feels like a terrible hack. Is this the right way to go considering this service is type dbus, so sd_notify doesn't really change the status anyway?
See https://github.com/heftig/rtkit/blob/c295fa849f52b487be6433e69e08b46251950399/rtkit-daemon.service.in#L23
According to service docs the notification is only interesting in case of Type=notify.
On fedora for example this works without log spam and without specific socket mapping.

Or from a different angle: What does having a "Status" line do for us in a service which is actively managed through a specified dbus topic?

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@dasJ dasJ Jul 4, 2022 •
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sd_notify works with non-notify services as well. The reason to use Type=notify is startup notifications, not whether sd_notify() works. That is controlled by NotifyAccess=.

The Status: line is Status: "Supervising 0 threads of 0 processes of 0 users.", which is the same as the debug message that is logged constantly.
Fixing the status line is pretty irrelevant to me, I don't care about it at all, I just implemented it so people who care about the info that is being logged constantly have a way of accessing it that isn't annoying.

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Digging into this more, adding notification won't influence the logs, since they're both sent anyway: https://github.com/heftig/rtkit/blob/c295fa849f52b487be6433e69e08b46251950399/rtkit-daemon.c#L1435-L1446

I think bumping up the log level is a good idea, but otherwise the behaviour should be either fixed upstream or patched. The whole chroot("/proc") could be replaced with a strict filesystem protection at service level anyway which would unbreak the status notification. (disable do_chroot) But messing with mounting over random /proc directories is just... yuck.

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Agree but it was disabling chroot() vs messing with /proc and while I agree with you that this is very ugly, it's the solution that doesn't lower security.

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Or to make it more clear: I'm not happy with this solution at all but it shuts up the daemon while not supressing info that was available previously. And upstream does not seem to care at all: heftig/rtkit#26

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We can replicate the chroot with TemporaryFileSystem and BindPaths and then disable the chroot the application creates itself.

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Something like this should work:

ProtectSystem=strict
PrivateDevices=true
InaccessiblePaths=/etc
TemporaryFileSystem=/var
BindPaths=/run/systemd/notify
SystemCallFilter=~@mount

(not tested)

TemporaryFileSystem = "/proc/fs";
# Only log LOG_INFO and higher
LogLevelMax = 6;
};
};

services.dbus.packages = [ pkgs.rtkit ];

users.users.rtkit =
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