Some of these checks before bitwise operations are redundant and compilers
do not always recognize them, so let's simplify the code to make the intentions
clearer.
Sometimes it makes sense to hard kill a client if we die. Let's hence
add a third FORK_DEATHSIG flag for this purpose: FORK_DEATHSIG_SIGKILL.
To make things less confusing this also renames FORK_DEATHSIG to
FORK_DEATHSIG_SIGTERM to make clear it sends SIGTERM. We already had
FORK_DEATHSIG_SIGINT, hence this makes things nicely symmetric.
A bunch of users are switched over for FORK_DEATHSIG_SIGKILL where we
know it's safe to abort things abruptly. This should make some kernel
cases more robust, since we cannot get confused by signal masks or such.
While we are at it, also fix a bunch of bugs where we didn't take
FORK_DEATHSIG_SIGINT into account in safe_fork()
If we have a DDI that contains only a /usr/ tree (and which is thus
combined with a tmpfs for root on boot) we previously would try to apply
idmapping to the tmpfs, but not the /usr/ mount. That's broken of
course.
Fix this by applying it to both trees.
We use it for more than just pipe() arrays. For example also for
socketpair(). Hence let's give it a generic name.
Also add EBADF_TRIPLET to mirror this for things like
stdin/stdout/stderr arrays, which we use a bunch of times.
Instead of mounting over, do an atomic swap using mount beneath, if
available. This way assets can be mounted again and again (e.g.:
updates) without leaking mounts.
The parsing is done after the image has been opened, not before, as it
cannot be done on an block device. Also fix returning on any error for
ExtensionDirectories, not just ENOENT.
Follow-up for 55ea4ef096
Let's add two new helpers: mount_credentials_fs() and
credentials_fs_mount_flags(). The former mounts a file system suitable
for storing of unencrypted credentials at runtime (i.e. a ramfs or
tmpfs). The latter determines the right mount flags to use for such a
mount.
Both functions mostly just take code from execute.c, but make two
changes:
1. If the kernel supports it we'll use a tmpfs with the new "noswap"
mount option instead of ramfs. Was added in kernel 6.4, hence is very
recent, but tmpfs is so much less crappy than ramfs, hence worth it.
2. We'll set MS_NOSYMFOLLOW on the mounts if supported. These file
systems should only contain regulra files, hence no need to allow
symlinks.
Fine-tune the decoding of mount options in mount_verbose_full() to
provide more helpful log output:
1. decode changing of propagation changes
2. discern changing of superblock flags/mount option string from mount
flags
3. don't check secondary fields when deciding which mount op is
executed, only the flags decide that.
That way, if we end up unmounting /proc/ in our loop we can still
operate correctly, since we don't have to go through /proc/ again to
open the mount table again.
There's no need to fchdir() out of the rootfs and back into it around
the umount2(), hence don't.
This brings the logic closer to what the pivot_root() man page suggests.
While we are at it, always operate based on fds, once we opened the
original dir, and pass the path string along only for generating
messages (i.e. as "decoration").
Add tests for both code paths: the pivot_root() one and the MS_MOUNT.
This will make things a bit longer for now, but more powerful as we can
reuse the userns fd between calls to remount_idmap() if we need to
adjust multiple mounts.
No change in behaviour, just some minor refactoring.
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.
This is useful when creating a new network namespace. Unlike procfs,
we need to remount sysfs, otherwise properties of the network interfaces
in the main network namespace are still accessible through the old sysfs,
e.g. /sys/class/net/eth0. All sub-mounts previously mounted on the sysfs
are moved onto the new sysfs mount.
The function will be used in later commits.
-1 was used everywhere, but -EBADF or -EBADFD started being used in various
places. Let's make things consistent in the new style.
Note that there are two candidates:
EBADF 9 Bad file descriptor
EBADFD 77 File descriptor in bad state
Since we're initializating the fd, we're just assigning a value that means
"no fd yet", so it's just a bad file descriptor, and the first errno fits
better. If instead we had a valid file descriptor that became invalid because
of some operation or state change, the other errno would fit better.
In some places, initialization is dropped if unnecessary.
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.
If the flag is set, we mount /tmp/ in a way that is suitable for generators and
other quick jobs.
Unfortunately I had to move some code from shared/mount-util.c to
basic/mountpoint-util.c. The functions that are moved are very thin wrappers
around mount(2), so this doesn't actually change much in the code split between
libbasic and libshared.
Implications for the host would be weird if a private mount namespace is not
used, so assert on FORK_NEW_MOUNTNS when the flag is used.
In order to support pivot_root() we need to move mount propagation
changes after the pivot_root(). While MS_MOVE requires the source mount
to not be a shared mount pivot_root() also requires the target mount to
not be a shared mount. This guarantees that pivot_root() doesn't leak
any mounts.
Signed-off-by: Christian Brauner (Microsoft) <brauner@kernel.org>
Currently, services use mount_move_root() in order to setup the root
directory of services using a mount namespace. This relies on MS_MOVE
and chroot(). However, this has serious drawbacks even for relatively
simple mount propagation scenarios.
What systemd currently does is roughly equivalent to the following shell
code:
unshare --mount --propagation=shared
cd /
mount --make-rslave /
mkdir /new-root
mount --rbind / /new-root
cd /new-root
mount --move /new-root /
chroot .
This looks simple enough but has the consequence that two separate mount
trees exist for the lifetime of the service. The first one was created
when the mount namespace was created, and the second one when a new
mount for the rootfs was created. The first mount tree sticks around as
a shadow mount tree. Both mount trees are dependent mounts with the host
rootfs as their dominating mount.
Now, when mount propagation is triggered by the host by e.g.,
mount --bind /opt /mnt
it means that two propagation events are generated. I'm skipping over
the exact kernel details as they aren't that important. The gist is that
for every propagation event that is generated a second one is generated
for the shadow mount tree. In other words, the kernel creates two copies
for each mount that is propagated instead of one.
This isn't necessary. We can simply change the sequence above to:
unshare --mount --propagation=shared
cd /
mount --make-rslave /
mkdir /new-root
# stash fd to old rootfs
# stash fd to new rootfs
mount --rbind / /new-root
mkdir /new-root
cd /new-root
pivot_root . .
# new root is tucked under old root
# chdir into old rootfs via stashed fd
umount -l /old-root
The pivot_root allows us to get rid of the old mount tree that was
created when the mount namespace was created. So after this sequence
only one mount tree is alive. Plus, it's safer and nicer. Moving mounts
isn't pleasnt.
This patch doesn't convert nspawn yet as the requirements are more
tricky given that it wants to preserve the rootfs as a shared mount
which goes against pivot_root() requirements.
Signed-off-by: Christian Brauner (Microsoft) <brauner@kernel.org>
Yu Watanabe
AtariDreams
Lennart Poettering
Luca Boccassi
Mike Yuan
Daan De Meyer
Zbigniew Jędrzejewski-Szmek
Christian Brauner