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set up a per-service session kernel keyring, and store the invocation ID in it
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This adds two new settings BindPaths= and BindReadOnlyPaths=. They allow
defining arbitrary bind mounts specific to particular services. This is
particularly useful for services with RootDirectory= set as this permits making
specific bits of the host directory available to chrooted services.
The two new settings follow the concepts nspawn already possess in --bind= and
--bind-ro=, as well as the .nspawn settings Bind= and BindReadOnly= (and these
latter options should probably be renamed to BindPaths= and BindReadOnlyPaths=
too).
Fixes: #3439
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Let's store the invocation ID in the per-service keyring as a root-owned key,
with strict access rights. This has the advantage over the environment-based ID
passing that it also works from SUID binaries (as they key cannot be overidden
by unprivileged code starting them), in contrast to the secure_getenv() based
mode.
The invocation ID is now passed in three different ways to a service:
- As environment variable $INVOCATION_ID. This is easy to use, but may be
overriden by unprivileged code (which might be a bad or a good thing), which
means it's incompatible with SUID code (see above).
- As extended attribute on the service cgroup. This cannot be overriden by
unprivileged code, and may be queried safely from "outside" of a service.
However, it is incompatible with containers right now, as unprivileged
containers generally cannot set xattrs on cgroupfs.
- As "invocation_id" key in the kernel keyring. This has the benefit that the
key cannot be changed by unprivileged service code, and thus is safe to
access from SUID code (see above). But do note that service code can replace
the session keyring with a fresh one that lacks the key. However in that case
the key will not be owned by root, which is easily detectable. The keyring is
also incompatible with containers right now, as it is not properly namespace
aware (but this is being worked on), and thus most container managers mask
the keyring-related system calls.
Ideally we'd only have one way to pass the invocation ID, but the different
ways all have limitations. The invocation ID hookup in journald is currently
only available on the host but not in containers, due to the mentioned
limitations.
How to verify the new invocation ID in the keyring:
# systemd-run -t /bin/sh
Running as unit: run-rd917366c04f847b480d486017f7239d6.service
Press ^] three times within 1s to disconnect TTY.
# keyctl show
Session Keyring
680208392 --alswrv 0 0 keyring: _ses
250926536 ----s-rv 0 0 \_ user: invocation_id
# keyctl request user invocation_id
250926536
# keyctl read 250926536
16 bytes of data in key:
9c96317c ac64495a a42b9cd7 4f3ff96b
# echo $INVOCATION_ID
9c96317cac64495aa42b9cd74f3ff96b
# ^D
This creates a new transient service runnint a shell. Then verifies the
contents of the keyring, requests the invocation ID key, and reads its payload.
For comparison the invocation ID as passed via the environment variable is also
displayed.
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This patch ensures that each system service gets its own session kernel keyring
automatically, and implicitly. Without this a keyring is allocated for it
on-demand, but is then linked with the user's kernel keyring, which is OK
behaviour for logged in users, but not so much for system services.
With this change each service gets a session keyring that is specific to the
service and ceases to exist when the service is shut down. The session keyring
is not linked up with the user keyring and keys hence only search within the
session boundaries by default.
(This is useful in a later commit to store per-service material in the keyring,
for example the invocation ID)
(With input from David Howells)
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Confirm spawn fixes/enhancements
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For some reasons units remaining in the same process group as PID 1
(same_pgrp=true) fail to acquire the console even if it's not taken by anyone.
So always accept for units with same_pgrp set for now.
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timed out
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Previously it was "[Yes, Fail, Skip]" which is pretty misleading because it
suggests that the whole word needs to be entered instead of a single char.
Also this won't fit well when we'll extend the number of choices.
This patch addresses this by changing the choice hint with "[y, f, s – h for help]"
so it's now clear that a single letter has to be entered.
It also introduces a new choice 'h' which describes all possible choices since
a single letter can be not descriptive enough for new users.
It also allow to stick with the same hint string regardless of how
many choices we will support.
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When "confirmation_spawn=1", the confirmation question can look like:
Execute /usr/bin/kmod static-nodes --format=tmpfiles --output=/run/tmpfiles.d/kmod.conf? [Yes, No, Skip]
which is pretty verbose and might not fit in the console width size (which is
usually 80 chars) and thus question will be splitted into 2 consecutive lines.
However since the question is now refreshed every 2 secs, the reprinted
question will overwrite the second line of the previous one...
To prevent this, this patch makes sure that the command line won't be longer
than 60 chars by ellipsizing it if the command is longer:
Execute /usr/bin/kmod static-nodes --format=tmpfiles --output=/ru…nf? [Yes, No, View, Skip]
A following patch will introduce a new choice that will allow the user to get
details on the command to be executed so it will still be possible to see the
full command line.
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Before this patch we had:
- "no" which gives "failing execution" but the command is actually assumed as
succeed.
- "skip" which gives "skipping", but the command is assumed to have failed,
which ends up with "Failed to start ..." on the console.
Now we have:
- "fail" which gives "failing execution" and the command is indeed assumed as
failed.
- "skip" which gives "skipping execution" and the command is assumed as
succeed.
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Now the reponses are handled by ask_for_confirmation() as well as the report of
any errors occuring during the process of retrieving the confirmation response.
One benefit of this is that there's no need to open/close the console one more
time when reporting error/status messages.
The caller now just needs to care about the return values whose meanings are:
- don't execute and pretend that the command failed
- don't execute and pretend that the command succeeed
- positive answer, execute the command
Also some slight code reorganization and introduce write_confirm_error() and
write_confirm_error_fd(). write_confim_message becomes unneeded.
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It's rather hard to parse the confirmation messages (enabled with
systemd.confirm_spawn=true) amongst the status messages and the kernel
ones (if enabled).
This patch gives the possibility to the user to redirect the confirmation
message to a different virtual console, either by giving its name or its path,
so those messages are separated from the other ones and easier to read.
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The no_new_privileged_set variable is not used any more since commit
9b232d3241fcfbf60af that fixed another thing. So remove it. Also no
need to check if we are under user manager, remove that part too.
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(#4596)
This adds a variable that is always set to false to make sure that
protect paths inside sandbox are always enforced and not ignored. The only
case when it is set to true is on DynamicUser=no and RootDirectory=/chroot
is set. This allows users to use more our sandbox features inside RootDirectory=
The only exception is ProtectSystem=full|strict and when DynamicUser=yes
is implied. Currently RootDirectory= is not fully compatible with these
due to two reasons:
* /chroot/usr|etc has to be present on ProtectSystem=full
* /chroot// has to be a mount point on ProtectSystem=strict.
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core: add new RestrictNamespaces= unit file setting
Merging, not rebasing, because this touches many files and there were tree-wide cleanups in the mean time.
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We don't have plural in the name of any other -util files and this
inconsistency trips me up every time I try to type this file name
from memory. "formats-util" is even hard to pronounce.
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This new setting permits restricting whether namespaces may be created and
managed by processes started by a unit. It installs a seccomp filter blocking
certain invocations of unshare(), clone() and setns().
RestrictNamespaces=no is the default, and does not restrict namespaces in any
way. RestrictNamespaces=yes takes away the ability to create or manage any kind
of namspace. "RestrictNamespaces=mnt ipc" restricts the creation of namespaces
so that only mount and IPC namespaces may be created/managed, but no other
kind of namespaces.
This setting should be improve security quite a bit as in particular user
namespacing was a major source of CVEs in the kernel in the past, and is
accessible to unprivileged processes. With this setting the entire attack
surface may be removed for system services that do not make use of namespaces.
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Tree wide cleanups
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is set
Make sure that when DynamicUser= is set that we intialize the user
supplementary groups and that we also support SupplementaryGroups=
Fixes: https://github.com/systemd/systemd/issues/4539
Thanks Evgeny Vereshchagin (@evverx)
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more seccomp fixes, and change of order of selinux/aa/smack and seccomp application on exec
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(#4533)
Always initialize the supplementary groups of caller before checking the
unit SupplementaryGroups= option.
Fixes https://github.com/systemd/systemd/issues/4531
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Seccomp is generally an unprivileged operation, changing security contexts is
most likely associated with some form of policy. Moreover, while seccomp may
influence our own flow of code quite a bit (much more than the security context
change) make sure to apply the seccomp filters immediately before executing the
binary to invoke.
This also moves enforcement of NNP after the security context change, so that
NNP cannot affect it anymore. (However, the security policy now has to permit
the NNP change).
This change has a good chance of breaking current SELinux/AA/SMACK setups, because
the policy might not expect this change of behaviour. However, it's technically
the better choice I think and should hence be applied.
Fixes: #3993
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seccomp: also block shmat(..., SHM_EXEC) for MemoryDenyWriteExecute
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This makes applying groups after applying the working directory, this
may allow some flexibility but at same it is not a big deal since we
don't execute or do anything between applying working directory and
droping groups.
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Improve apply_working_directory() and lets get the current working directory
inside of it.
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shmat(..., SHM_EXEC) can be used to create writable and executable
memory, so let's block it when MemoryDenyWriteExecute is set.
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This allows us to unify most of the code in apply_protect_kernel_modules() and
apply_private_devices().
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This adds a new seccomp_init_conservative() helper call that is mostly just a
wrapper around seccomp_init(), but turns off NNP and adds in all secondary
archs, for best compatibility with everything else.
Pretty much all of our code used the very same constructs for these three
steps, hence unifying this in one small function makes things a lot shorter.
This also changes incorrect usage of the "scmp_filter_ctx" type at various
places. libseccomp defines it as typedef to "void*", i.e. it is a pointer type
(pretty poor choice already!) that casts implicitly to and from all other
pointer types (even poorer choice: you defined a confusing type now, and don't
even gain any bit of type safety through it...). A lot of the code assumed the
type would refer to a structure, and hence aded additional "*" here and there.
Remove that.
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seccomp_add_syscall_filter_set()
Let's simplify this call, by making use of the new infrastructure.
This is actually more in line with Djalal's original patch but instead of
search the filter set in the array by its name we can now use the set index and
jump directly to it.
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A variety of fixes:
- rename the SystemCallFilterSet structure to SyscallFilterSet. So far the main
instance of it (the syscall_filter_sets[] array) used to abbreviate
"SystemCall" as "Syscall". Let's stick to one of the two syntaxes, and not
mix and match too wildly. Let's pick the shorter name in this case, as it is
sufficiently well established to not confuse hackers reading this.
- Export explicit indexes into the syscall_filter_sets[] array via an enum.
This way, code that wants to make use of a specific filter set, can index it
directly via the enum, instead of having to search for it. This makes
apply_private_devices() in particular a lot simpler.
- Provide two new helper calls in seccomp-util.c: syscall_filter_set_find() to
find a set by its name, seccomp_add_syscall_filter_set() to add a set to a
seccomp object.
- Update SystemCallFilter= parser to use extract_first_word(). Let's work on
deprecating FOREACH_WORD_QUOTED().
- Simplify apply_private_devices() using this functionality
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Let's prefer early-exit over deep-indented if blocks. Not behavioural change.
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Remove the assert and check the return code of sysconf(_SC_NGROUPS_MAX).
_SC_NGROUPS_MAX maps to NGROUPS_MAX which is defined in <limits.h> to
65536 these days. The value is a sysctl read-only
/proc/sys/kernel/ngroups_max and the kernel assumes that it is always
positive otherwise things may break. Follow this and support only
positive values for all other case return either -errno or -EOPNOTSUPP.
Now if there are systems that want to re-write NGROUPS_MAX then they
should not pass SupplementaryGroups= in units even if it is empty, in
this case nothing fails and we just ignore supplementary groups. However
if SupplementaryGroups= is passed even if it is empty we have to assume
that there will be groups manipulation from our side or the kernel and
since the kernel always assumes that NGROUPS_MAX is positive, then
follow that and support only positive values.
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This is minor but lets try to split and move bit by bit cgroups and
portable environment setup before applying the security context.
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This fixes: https://github.com/systemd/systemd/issues/4357
Let's lookup and cache creds then apply them. We also switch from
getgroups() to getgrouplist().
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This makes strjoin and strjoina more similar and avoids the useless final
argument.
spatch -I . -I ./src -I ./src/basic -I ./src/basic -I ./src/shared -I ./src/shared -I ./src/network -I ./src/locale -I ./src/login -I ./src/journal -I ./src/journal -I ./src/timedate -I ./src/timesync -I ./src/nspawn -I ./src/resolve -I ./src/resolve -I ./src/systemd -I ./src/core -I ./src/core -I ./src/libudev -I ./src/udev -I ./src/udev/net -I ./src/udev -I ./src/libsystemd/sd-bus -I ./src/libsystemd/sd-event -I ./src/libsystemd/sd-login -I ./src/libsystemd/sd-netlink -I ./src/libsystemd/sd-network -I ./src/libsystemd/sd-hwdb -I ./src/libsystemd/sd-device -I ./src/libsystemd/sd-id128 -I ./src/libsystemd-network --sp-file coccinelle/strjoin.cocci --in-place $(git ls-files src/*.c)
git grep -e '\bstrjoin\b.*NULL' -l|xargs sed -i -r 's/strjoin\((.*), NULL\)/strjoin(\1)/'
This might have missed a few cases (spatch has a really hard time dealing
with _cleanup_ macros), but that's no big issue, they can always be fixed
later.
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This commit adds a `fd` option to `StandardInput=`,
`StandardOutput=` and `StandardError=` properties in order to
connect standard streams to externally named descriptors provided
by some socket units.
This option looks for a file descriptor named as the corresponding
stream. Custom names can be specified, separated by a colon.
If multiple name-matches exist, the first matching fd will be used.
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Lets go further and make /lib/modules/ inaccessible for services that do
not have business with modules, this is a minor improvment but it may
help on setups with custom modules and they are limited... in regard of
kernel auto-load feature.
This change introduce NameSpaceInfo struct which we may embed later
inside ExecContext but for now lets just reduce the argument number to
setup_namespace() and merge ProtectKernelModules feature.
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This is useful to turn off explicit module load and unload operations on modular
kernels. This option removes CAP_SYS_MODULE from the capability bounding set for
the unit, and installs a system call filter to block module system calls.
This option will not prevent the kernel from loading modules using the module
auto-load feature which is a system wide operation.
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