This is establish the basic concepts for #35685, in the hope to get this
merged first.
This defines a special, fixed 64K UID range that is supposed to be used
by directory container images on disk, that is mapped to a dynamic UID
range at runtime (via idmapped mounts).
This enables a world where each container can run with a dynamic UID
range, but this in no way leaks onto the disk, thus making supposedly
dynamic, transient UID range assignments persistent.
This is infrastructure later used for the primary part of #35685: unpriv
container execution with directory images inside user's home dirs, that
are assigned to this special "foreign UID range".
This PR only defines the ranges, synthesizes NSS records for them via
userdb, and then exposes them in a new "systemd-dissect --shift" command
that can re-chown a container directory tree into this range (and in
fact any range).
This comes with docs. But no tests. There are tests in #35685 that cover
all this, but they are more comprehensive and also test nspawn's hook-up
with this, hence are excluded from this PR.
This makes sure when we are blocking signals in preparation for fork()
we'll not temporarily unblock any signals previously set, by mistake.
It's safe for us to block more, but not to unblock signals already
blocked. Fix that.
Fixes: #35470
This makes the UID range configurable via build time options, but of
course it really shouldn't be changed. The default range I picked is
outside even of IPAs current (ridiculously large) allocation ranges,
hence hopefully minimizes conflicts.
Avoid showing the files on the ESP (i.e. a FAT formatted volume) as
executable by removing the execute permission from them.
IMO this makes the colored output of `ls` more sensible since the file
system will be mounted with `noexec` anyway.
Add a `fstype_can_fmask_dmask` function that checks if a file system
type can use the `fmask` and `dmask` mount options.
This replaces `fstype_can_umask` since it was only used in
`partition_pick_mount_options` which only cares about the file system
support for fmask & dmask now.
It somewhat reduces the coverage of the feature since there are more file
systems that support umask as opposed to those supporting dmask & dmask,
but it should not be much of an issue since fmask & dmask are supported
by vfat, exfat and ntfs3.
This makes sure the the codepath that derives an nsfd from a pid works
the same for the pidfd case and the non-pidfd case: if we can verify
that /proc/ is mounted but the /proc/$PID/ns/ files are missing, we can
assume the ns type is not supported by the kernel. Hence return the same
ENOPKG error in this case as we already do in the pidfd ioctl based
codepath.
As requested, a list of kernel version to feature mapping
for kernels older than minimum baseline is also included,
in order to ease potential backport work.
This is something I think we should have added a long time ago: a
flavour of open() that safely ensures the inode we are opening is a
regular file, before we open it. It does this by means of pinning the
inode via O_PATH first, and after verification actually opening it.
This ports some code over to this, but sooner or later we should
probably use this a lot more, so that we don't accidentally open weird
stuff such as device nodes or pipes, where we should not.
Supersedes #35308 (cherry-picked one commit and replaced the rest)
(I left a few comments that's folded by GitHub. Please make sure to
check them too.)
- Make fd_is_namespace() take NamespaceType
- Drop support for kernel without NS_GET_NSTYPE (< 4.11)
- Port is_our_namespace() to namespace_open_by_type()
(preparation for later commits, where the latter
would go by pidfd if available, avoiding procfs)
Lennart Poettering
Ivan Kruglov
Mike Yuan
nl6720
Yu Watanabe
Daan De Meyer