Chasing symlinks is a core function that's used in a lot of places
so it deservers a less verbose names so let's rename it to chase()
and chaseat().
We also slightly change the pattern used for the chaseat() helpers
so we get chase_and_openat() and similar.
We bind mount two selected inodes from the host into our container.
Let's turn off propagation for that, since we just want those inodes,
nothing else.
With this change "grep master: /proc/self/mountinfo" should list only
the mount propagation "tunnel" dir, and nothing else anymore.
When using --private-users, we have to create bind mount points as
the user that will become root in the user namespace, so let's take
that into account.
This is an octal number. We used the 0 prefix in some places inconsistently.
The kernel always interprets in base-8, so this has no effect, but I think
it's nicer to use the 0 to remind the reader that this is not a decimal number.
In order to mount procfs and sysfs in an unprivileged container the
kernel requires that a fully visible instance is already present in the
target mount namespace. Mount one here so the inner child can mount its
own instances. Later we umount the temporary instances created here
before we actually exec the payload. Since the rootfs is shared the
umount will propagate into the container. Note, the inner child wouldn't
be able to unmount the instances on its own since it doesn't own the
originating mount namespace. IOW, the outer child needs to do this.
So far nspawn didn't run into this issue because it used MS_MOVE which
meant that the shadow mount tree pinned a procfs and sysfs instance
which the kernel would find. The shadow mount tree is gone with proper
pivot_root() semantics.
Signed-off-by: Christian Brauner (Microsoft) <brauner@kernel.org>
In most cases we refernced the concept as "initrd". Let's convert most
remaining uses of "initramfs" to "initrd" too, to stay internally
consistent.
This leaves "initramfs" only where it's relevant to explain historical
concepts or where "initramfs" is part of the API (i.e. in
/run/initramfs).
Follow-up for: b66a6e1a58
rootidmap bind option will map the root user from the container to the
owner of the mounted directory on the filesystem. This will ensure files
and directories created by the root user in the container will be owned
by the directory owner on the filesystem. All other user will remain
unmapped.
This enum should be used to define various idmapping modes for bind
mounts which might be incompatible. Changing its name and the values
name to reflect that.
Follow-up for 4c733d3046.
Finding a suitable limit that would fit any use cases out there is pretty hard
and since /dev is only writeable by root anyway, let's simply drop the limit.
Same idea as 03677889f0.
No functional change intended. The type of the iterator is generally changed to
be 'const char*' instead of 'char*'. Despite the type commonly used, modifying
the string was not allowed.
I adjusted the naming of some short variables for clarity and reduced the scope
of some variable declarations in code that was being touched anyway.
When using user namespaces in conjunction with uidmapped mounts, nspawn
so far set up two uidmappings:
1. One that is used for the uidmapped mount and that maps the UID range
0…65535 on the backing fs to some high UID range X…X+65535 on the
uidmapped fs. (Let's call this mapping the "mount mapping")
2. One that is used for the userns namespace the container payload
processes run in, that maps X…X+65535 back to 0…65535. (Let's call
this one the "process mapping").
These mappings hence are pretty much identical, one just moves things up
and one back down. (Reminder: we do all this so that the processes can
run under high UIDs while running off file systems that require no
recursive chown()ing, i.e. we want processes with high UID range but
files with low UID range.)
This creates one problem, i.e. issue #20989: if nspawn (which runs as
host root, i.e. host UID 0) wants to add inodes to the uidmapped mount
it can't do that, since host UID 0 is not defined in the mount mapping
(only the X…X+65536 range is, after all, and X > 0), and processes whose
UID is not mapped in a uidmapped fs cannot create inodes in it since
those would be owned by an unmapped UID, which then triggers
the famous EOVERFLOW error.
Let's fix this, by explicitly including an entry for the host UID 0 in
the mount mapping. Specifically, we'll extend the mount mapping to map
UID 2147483646 (which is INT32_MAX-1, see code for an explanation why I
picked this one) of the backing fs to UID 0 on the uidmapped fs. This
way nspawn can creates inode on the uidmapped as it likes (which will
then actually be owned by UID 2147483646 on the backing fs), and as it
always did. Note that we do *not* create a similar entry in the process
mapping. Thus any files created by nspawn that way (and not chown()ed to
something better) will appear as unmapped (i.e. as overflowuid/"nobody")
in the container payload. And that's good. Of course, the latter is
mostly theoretic, as nspawn should generally chown() the inodes it
creates to UID ranges that actually make sense for the container (and we
generally already do this correctly), but it#s good to know that we are
safe here, given we might accidentally forget to chown() some inodes we
create.
Net effect: the two mappings will not be identical anymore. The mount
mapping has one entry more, and the only reason it exists is so that
nspawn can access the uidmapped fs reasonably independently from any
process mapping.
Fixes: #20989
Previously the mkdir_label() family of calls was implemented in
src/shared/mkdir-label.c but its functions partly declared ins
src/shared/label.h and partly in src/basic/mkdir.h (!!). That's weird
(and wrong).
Let's clean this up, and add a proper mkdir-label.h matching the .c
file.
This makes sure that a switch like --bind=:/foo does the right thing if
user namespacing is one: the backing dir should be owned by the
container's root UID not the host's. Thus, whenever the source path is
left empty and we automatically generate a source dir as temporary
directory, ensure it's owned by the right UID.
Fixes: #20869
In general we almost never hit those asserts in production code, so users see
them very rarely, if ever. But either way, we just need something that users
can pass to the developers.
We have quite a few of those asserts, and some have fairly nice messages, but
many are like "WTF?" or "???" or "unexpected something". The error that is
printed includes the file location, and function name. In almost all functions
there's at most one assert, so the function name alone is enough to identify
the failure for a developer. So we don't get much extra from the message, and
we might just as well drop them.
Dropping them makes our code a tiny bit smaller, and most importantly, improves
development experience by making it easy to insert such an assert in the code
without thinking how to phrase the argument.
Fixes a bug introduced by cfea7618f2.
Before this commit:
mode=1777,size=10%,nr_inodes=400k,uid=496107520,gid=496107520,context=,sys.id:sys.role:systemd.nspawn.container.fs:s0,
After this commit:
mode=1777,size=10%,nr_inodes=400k,uid=496107520,gid=496107520,context=sys.id:sys.role:systemd.nspawn.container.fs:s0
Fixes#19976.
Let's make umount_verbose() more like mount_verbose_xyz(), i.e. take log
level and flags param. In particular the latter matters, since we
typically don't actually want to follow symlinks when unmounting.
The explicit limit is dropped, which means that we return to the kernel default
of 50% of RAM. See 362a55fc14 for a discussion why that is not as much as it
seems. It turns out various applications need more space in /dev/shm and we
would break them by imposing a low limit.
While at it, rename the define and use a single macro for various tmpfs mounts.
We don't really care what the purpose of the given tmpfs is, so it seems
reasonable to use a single macro.
This effectively reverts part of 7d85383edb. Fixes#16617.
Let's find the right os-release file on the host side, and only mount
the one that matters, i.e. /etc/os-release if it exists and
/usr/lib/os-release otherwise. Use the fixed path /run/host/os-release
for that.
Let's also mount /run/host as a bind mount on itself before we set up
/run/host, and let's mount it MS_RDONLY after we are done, so that it
remains immutable as a whole.
The kernel interface requires setting up read-only bind-mounts in
two steps, the bind first and then a read-only remount.
Fix nspawn-mount, and cover this case in the integration test.
Fixes#16484
Since #15533 we didn't create the mount point for selinuxfs anymore.
Before it we created it twice because we mount selinuxfs twice: once the
superblock, and once we remount its bind mound read-only. The second
mkdir would mean we'd chown() the host version of selinuxfs (since
there's only one selinuxfs superblock kernel-wide).
The right time to create mount point point is once: before we mount the
selinuxfs. But not a second time for the remount.
Fixes: #16032
Let's make sure $XDG_RUNTIME_DIR for the user instance and /run for the
system instance is always organized the same way: the "inaccessible"
device nodes should be placed in a subdir of either called "systemd" and
a subdir of that called "inaccessible".
This way we can emphasize the common behaviour, and only differ where
really necessary.
Follow-up for #13823
Limit size of various tmpfs mounts to 10% of RAM, except volatile root and /var
to 25%. Another exception is made for /dev (also /devs for PrivateDevices) and
/sys/fs/cgroup since no (or very few) regular files are expected to be used.
In addition, since directories, symbolic links, device specials and xattrs are
not counted towards the size= limit, number of inodes is also limited
correspondingly: 4MB size translates to 1k of inodes (assuming 4k each), 10% of
RAM (using 16GB of RAM as baseline) translates to 400k and 25% to 1M inodes.
Because nr_inodes option can't use ratios like size option, there's an
unfortunate side effect that with small memory systems the limit may be on the
too large side. Also, on an extremely small device with only 256MB of RAM, 10%
of RAM for /run may not be enough for re-exec of PID1 because 16MB of free
space is required.
To support ProtectHome=y in a user namespace (which mounts the inaccessible
nodes), the nodes need to be accessible by the user. Create these paths and
devices in the user runtime directory so they can be used later if needed.
This makes --overlay=+/foobar::/foobar work again, i.e. where the middle
parameter is left out. According to the documentation this is supposed
to generate a temporary writable work place in the midle. But it
apparently never did. Weird.
chase_symlinks() would return negative on error, and either a non-negative status
or a non-negative fd when CHASE_OPEN was given. This made the interface quite
complicated, because dependning on the flags used, we would get two different
"types" of return object. Coverity was always confused by this, and flagged
every use of chase_symlinks() without CHASE_OPEN as a resource leak (because it
would this that an fd is returned). This patch uses a saparate output parameter,
so there is no confusion.
(I think it is OK to have functions which return either an error or an fd. It's
only returning *either* an fd or a non-fd that is confusing.)
Daan De Meyer
Frantisek Sumsal
Lennart Poettering
Zbigniew Jędrzejewski-Szmek
Christian Brauner
David Tardon
Quentin Deslandes
Quentin Deslandes
Franck Bui
Yu Watanabe
Andreas Valder
Luca Boccassi
Topi Miettinen
Daan De Meyer
Anita Zhang