6dfd290031
Recently, PrivateUsers=identity was added to support mapping the first 65536 UIDs/GIDs from parent to the child namespace and mapping the other UID/GIDs to the nobody user. However, there are use cases where users have UIDs/GIDs > 65536 and need to do a similar identity mapping. Moreover, in some of those cases, users want a full identity mapping from 0 -> UID_MAX. To support this, we add PrivateUsers=full that does identity mapping for all available UID/GIDs. Note to differentiate ourselves from the init user namespace, we need to set up the uid_map/gid_map like: ``` 0 0 1 1 1 UINT32_MAX - 1 ``` as the init user namedspace uses `0 0 UINT32_MAX` and some applications - like systemd itself - determine if its a non-init user namespace based on uid_map/gid_map files. Note systemd will remove this heuristic in running_in_userns() in version 258 (https://github.com/systemd/systemd/pull/35382) and uses namespace inode. But some users may be running a container image with older systemd < 258 so we keep this hack until version 259 for version N-1 compatibility. In addition to mapping the whole UID/GID space, we also set /proc/pid/setgroups to "allow". While we usually set "deny" to avoid security issues with dropping supplementary groups (https://lwn.net/Articles/626665/), this ends up breaking dbus-broker when running /sbin/init in full OS containers. Fixes: #35168 Fixes: #35425
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