(RHEL-70103) journal: again create user journals for users with high uids

[jamacku]

This effectively reverts a change in 115d514 'journald: move uid_for_system_journal() to uid-alloc-range.h', which slipped in an additional check of uid_is_container(uid). The problem is that that change is not backwards-compatible at all and very hard for users to handle. There is no common agreement on mappings of high-range uids. Systemd declares ownership of a large range for container uids in https://systemd.io/UIDS-GIDS/, but this is only a recent change and various sites allocated those ranges in a different way, in particular FreeIPA uses (used?) uids from this range for human users. On big sites with lots of users changing uids is obviously a hard problem. We generally assume that uids cannot be "freed" and/or changed and/or reused safely, so we shouldn't demand the same from others.

This is somewhat similar to the situation with SYSTEM_ALLOC_UID_MIN / SYSTEM_UID_MAX, which we tried to define to a fixed value in our code, causing huge problems for existing systems with were created with a different definition and couldn't be easily updated. For that case, we added a configuration time switch and we now parse /etc/login.defs to actually use the value that is appropriate for the local system.

Unfortunately, login.defs doesn't have a concept of container allocation ranges (and we don't have code to parse and use those nonexistent names either), so we can't tell users to adjust logind.defs to work around the changed definition.

login.defs has SUB_UID_{MIN,MAX}, but those aren't really the same thing, because they are used to define where the add allocations for subuids, which is generally a much smaller range. Maybe we should talk with other folks about the appropriate allocation ranges and define some new settings in login.defs. But this would require discussion and coordination with other projects first.

Actualy, it seems that this change was needed at all. The code in the container does not log to the outside journal. It talks to its own journald, which does journal splitting using its internal logic based on shifted uids. So let's revert the change to fix user systems.

Fixes https://bugzilla.redhat.com/show_bug.cgi?id=2251843.

Upstream PR: systemd/systemd#30846

rhel-only: bugfix

Resolves: RHEL-70103

[github-actions]

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Tracker - RHEL-70103

The following commits meet all requirements

commit	upstream
4ab0221 - journal: again create user journals for users with high uids	rhel-only: bugfix

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