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In https://bugzilla.redhat.com/show_bug.cgi?id=2156900 sysusers was reporting a
conflict between the following lines:
u root 0:0 "Super User" /root /bin/bash
u root 0 "Super User" /root
The problem is that those configurations are indeed not equivalent. If group 0
exists with a different name, the first line would just create the user, but the
second line would create a 'root' group with a different GID. The second
behaviour seems definitely wrong. (Or at least more confusing in practice than
the first one. The system is in a strange shape, but the second approach takes
an additional step than is worse than doing nothing.)
When this line was initially added, we didn't have the uid:gid functionality for
'u', so we didn't think about this too much. But now we do, so we should use it.
$ build/systemd-sysusers --root=/var/tmp/inst7 --inline 'g foobar 0'
Creating group 'foobar' with GID 0.
$ build/systemd-sysusers --root=/var/tmp/inst7 --inline 'u root 0 "Zuper zuper"'
src/sysusers/sysusers.c:1365: Creating group 'root' with GID 999.
src/sysusers/sysusers.c:1115: Suggested user ID 0 for root already used.
src/sysusers/sysusers.c:1183: Creating user 'root' (Zuper zuper) with UID 999 and GID 999.
vs.
$ build/systemd-sysusers --root=/var/tmp/inst7 --inline 'u root 0:0 "Zuper zuper"'
src/sysusers/sysusers.c:1183: Creating user 'root' (Zuper zuper) with UID 0 and GID 0.
On distros using Debian's base-passwd, the name of the group with gid 65534 is
nogroup. Currently, systemd-sysusers creates a spurious "nobody" group
systemd-sysusers[243]: Creating group nobody with gid 996
That's both confusing and redundant, as the nobody user still has primary group
65534 aka nogroup, and the nobody group simply goes completely unused.
So explicitly specify the primary group of the nobody user, and add a line
ensuring that that group exists.
This is not a problem for Debian (or Ubuntu) itself, as they add their own
version of basic.conf in their systemd build logic. But it appears on for
example Yocto/OpenEmbedded.
The general idea with users and groups created through sysusers is that an
appropriate number is picked when the allocation is made. The number that is
selected will be different on each system based on the order of creation of
users, installed packages, etc. Since system users and groups are not shared
between installations, this generally is not an issue. But it becomes a problem
for initrd: some file systems are shared between the initrd and the host (/run
and /dev are probably the only ones that matter). If the allocations are
different in the host and the initrd, and files survive switch-root, they will
have wrong ownership.
This makes the gids build-time-configurable for all groups and users where
state may survive the switch from initrd to the host.
In particular, all "hardware access" groups are like this: files in /dev will
be owned by them. Eventually the new udev would change ownership, but there
would be a momemnt where the files were owned by the wrong group. The
allocations are "soft-static" in the language of Fedora packaging guidelines:
the uid/gid will be used if possible, but we'll fall back to a different
one. TTY_GID is the exception, because the number is used directly.
Similarly, the possibility to configure "soft-static" uids is added for daemons
which may usefully run in the initramfs: systemd-network (lease information and
interface state is serialized to /run), systemd-resolve (stub files and
interface state), systemd-timesync (/run/systemd/timesync).
Journal files are owned by the group systemd-journal, and acls are granted
for wheel and adm.
systemd-oom and systemd-coredump are excluded from this patch: I assume that
oomd is not useful in the initrd, and coredump leaves no state (it only creates
a pipe in /run?).
The defaults are not changed: if nothing is configured, dynamic allocation will
be used. I looked at a Debian system, and the numbers are all different than
on Fedora.
For Fedora, see the list of uids and gids at https://pagure.io/setup/blob/master/f/uidgid.
In particular, systemd-network and systemd-resolve got soft-static numbers to
make it easy to transition from a non-host-specific initrd to a host system
already a few years back (https://bugzilla.redhat.com/show_bug.cgi?id=1102002).
I also requested static allocations for sgx, input, render in
https://pagure.io/packaging-committee/issue/1078,
https://pagure.io/setup/pull-request/27.
m4 was nice in '85, but the syntax feels a bit dated. Since we use python for
meson, let's use a popular python templating engine to replace some m4 usage.
A little nicety is that typos are caught:
FAILED: sysusers.d/systemd-remote.conf
/usr/bin/meson --internal exe --capture sysusers.d/systemd-remote.conf -- /home/zbyszek/src/systemd/tools/meson-render-jinja2.py config.h ../sysusers.d/systemd-remote.conf.j2
Traceback (most recent call last):
File "/home/zbyszek/src/systemd/tools/meson-render-jinja2.py", line 28, in <module>
print(render(sys.argv[2], defines))
File "/home/zbyszek/src/systemd/tools/meson-render-jinja2.py", line 24, in render
return template.render(defines)
File "/usr/lib/python3.9/site-packages/jinja2/environment.py", line 1090, in render
self.environment.handle_exception()
File "/usr/lib/python3.9/site-packages/jinja2/environment.py", line 832, in handle_exception
reraise(*rewrite_traceback_stack(source=source))
File "/usr/lib/python3.9/site-packages/jinja2/_compat.py", line 28, in reraise
raise value.with_traceback(tb)
File "<template>", line 8, in top-level template code
jinja2.exceptions.UndefinedError: 'HAVE_MICROHTTP' is undefined
This checking mirrors what 349cc4a507 did for C defines.
Closes#18669.
This creates a "well known" for sgx_enclave ownership. By doing this here we
avoid the risk that various projects making use of the device will provide
similar-but-slightly-incompatible installation instructions, in particular
using different group names.
ACLs are actually a better approach to grant access to users, but not in all
cases, so we want to provide a standard group anyway.
Mode is 0o660, not 0o666 because this is very new code and distributions are
likely to not want to give full access to all users. This might change in the
future, but being conservative is a good default in the beginning.
Rules for /dev/sgx_provision will be provided by libsg-ae-pce:
https://github.com/intel/linux-sgx/issues/678.
To allow better integration with distributions requiring an explicitly
set gid for the `users` group, provide the new `-Dusers-gid` option to
set to a new numeric value.
In the absence of a specified gid, we'll fallback to the default existing
behaviour of `-` as the gid value, to automatically assign the next available
gid on the system.
- Remove the uaccess tag from /dev/dri/renderD*.
- Change the owning group from video to render.
- Change default mode to 0666.
- Add an option to allow users to set the access mode for these devices at
compile time.
Kernel default mode is 0600, but distributions change it to group kvm, mode
either 0660 (e.g. Debian) or 0666 (e.g. Fedora). Both approaches have valid
reasons (a stricter mode limits exposure to bugs in the kvm subsystem, a looser
mode makes libvirt and other virtualization mechanisms work out of the box for
unprivileged users over ssh).
In Fedora the qemu package carries the relevant rule, but it's nicer to have it
in systemd, so that the permissions are not dependent on the qemu package being
installed. Use of packaged qemu binaries is not required to make use of
/dev/kvm, e.g. it's possible to use a self-compiled qemu or some alternative.
https://bugzilla.redhat.com/show_bug.cgi?id=1431876
To accomodate both approaches, add a rule to set the mode in 50-udev-default.rules,
but allow the mode to be overridden with a --with-dev-kvm-mode configure rule.
The default is 0660, as the (slightly) more secure option.
Hardly any software uses that any more, and better locking mechanisms like
flock() have been available for many years.
Also drop the corresponding "lock" group from sysusers.d/basic.conf.in, as
nothing else is using this.
