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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.
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.
This adds a new invocation ID concept to the service manager. The invocation ID
identifies each runtime cycle of a unit uniquely. A new randomized 128bit ID is
generated each time a unit moves from and inactive to an activating or active
state.
The primary usecase for this concept is to connect the runtime data PID 1
maintains about a service with the offline data the journal stores about it.
Previously we'd use the unit name plus start/stop times, which however is
highly racy since the journal will generally process log data after the service
already ended.
The "invocation ID" kinda matches the "boot ID" concept of the Linux kernel,
except that it applies to an individual unit instead of the whole system.
The invocation ID is passed to the activated processes as environment variable.
It is additionally stored as extended attribute on the cgroup of the unit. The
latter is used by journald to automatically retrieve it for each log logged
message and attach it to the log entry. The environment variable is very easily
accessible, even for unprivileged services. OTOH the extended attribute is only
accessible to privileged processes (this is because cgroupfs only supports the
"trusted." xattr namespace, not "user."). The environment variable may be
altered by services, the extended attribute may not be, hence is the better
choice for the journal.
Note that reading the invocation ID off the extended attribute from journald is
racy, similar to the way reading the unit name for a logging process is.
This patch adds APIs to read the invocation ID to sd-id128:
sd_id128_get_invocation() may be used in a similar fashion to
sd_id128_get_boot().
PID1's own logging is updated to always include the invocation ID when it logs
information about a unit.
A new bus call GetUnitByInvocationID() is added that allows retrieving a bus
path to a unit by its invocation ID. The bus path is built using the invocation
ID, thus providing a path for referring to a unit that is valid only for the
current runtime cycleof it.
Outlook for the future: should the kernel eventually allow passing of cgroup
information along AF_UNIX/SOCK_DGRAM messages via a unique cgroup id, then we
can alter the invocation ID to be generated as hash from that rather than
entirely randomly. This way we can derive the invocation race-freely from the
messages.
Make ALSA entries, latency interface, mtrr, apm/acpi, suspend interface,
filesystems configuration and IRQ tuning readonly.
Most of these interfaces now days should be in /sys but they are still
available through /proc, so just protect them. This patch does not touch
/proc/net/...
Let's merge a couple of columns, to make the table a bit shorter. This
effectively just drops whitespace, not contents, but makes the currently
humungous table much much more compact.
This reworks the documentation for ReadOnlyPaths=, ReadWritePaths=,
InaccessiblePaths=. It no longer claims that we'd follow symlinks relative to
the host file system. (Which wasn't true actually, as we didn't follow symlinks
at all in the most recent releases, and we know do follow them, but relative to
RootDirectory=).
This also replaces all references to the fact that all fs namespacing options
can be undone with enough privileges and disable propagation by a single one in
the documentation of ReadOnlyPaths= and friends, and then directs the read to
this in all other places.
Moreover a hint is added to the documentation of SystemCallFilter=, suggesting
usage of ~@mount in case any of the fs namespacing related options are used.
Let's drop the reference to the cap_from_name() function in the documentation
for the capabilities setting, as it is hardly helpful. Our readers are not
necessarily C hackers knowing the semantics of cap_from_name(). Moreover, the
strings we accept are just the plain capability names as listed in
capabilities(7) hence there's really no point in confusing the user with
anything else.
Let's make sure that services that use DynamicUser=1 cannot leave files in the
file system should the system accidentally have a world-writable directory
somewhere.
This effectively ensures that directories need to be whitelisted rather than
blacklisted for access when DynamicUser=1 is set.
Let's tighten our sandbox a bit more: with this change ProtectSystem= gains a
new setting "strict". If set, the entire directory tree of the system is
mounted read-only, but the API file systems /proc, /dev, /sys are excluded
(they may be managed with PrivateDevices= and ProtectKernelTunables=). Also,
/home and /root are excluded as those are left for ProtectHome= to manage.
In this mode, all "real" file systems (i.e. non-API file systems) are mounted
read-only, and specific directories may only be excluded via
ReadWriteDirectories=, thus implementing an effective whitelist instead of
blacklist of writable directories.
While we are at, also add /efi to the list of paths always affected by
ProtectSystem=. This is a follow-up for
b52a109ad3 which added /efi as alternative for
/boot. Our namespacing logic should respect that too.
This adds the boolean RemoveIPC= setting to service, socket, mount and swap
units (i.e. all unit types that may invoke processes). if turned on, and the
unit's user/group is not root, all IPC objects of the user/group are removed
when the service is shut down. The life-cycle of the IPC objects is hence bound
to the unit life-cycle.
This is particularly relevant for units with dynamic users, as it is essential
that no objects owned by the dynamic users survive the service exiting. In
fact, this patch adds code to imply RemoveIPC= if DynamicUser= is set.
In order to communicate the UID/GID of an executed process back to PID 1 this
adds a new "user lookup" socket pair, that is inherited into the forked
processes, and closed before the exec(). This is needed since we cannot do NSS
from PID 1 due to deadlock risks, However need to know the used UID/GID in
order to clean up IPC owned by it if the unit shuts down.
This should simplify monitoring tools for services, by passing the most basic
information about service result/exit information via environment variables,
thus making it unnecessary to retrieve them explicitly via the bus.
This setting adds minimal user namespacing support to a service. When set the invoked
processes will run in their own user namespace. Only a trivial mapping will be
set up: the root user/group is mapped to root, and the user/group of the
service will be mapped to itself, everything else is mapped to nobody.
If this setting is used the service runs with no capabilities on the host, but
configurable capabilities within the service.
This setting is particularly useful in conjunction with RootDirectory= as the
need to synchronize /etc/passwd and /etc/group between the host and the service
OS tree is reduced, as only three UID/GIDs need to match: root, nobody and the
user of the service itself. But even outside the RootDirectory= case this
setting is useful to substantially reduce the attack surface of a service.
Example command to test this:
systemd-run -p PrivateUsers=1 -p User=foobar -t /bin/sh
This runs a shell as user "foobar". When typing "ps" only processes owned by
"root", by "foobar", and by "nobody" should be visible.
As suggested by @mbiebl we already use the "!" special char in unit file
assignments for negation, hence we should not use it in a different context for
privileged execution. Let's use "+" instead.
This adds a new boolean setting DynamicUser= to service files. If set, a new
user will be allocated dynamically when the unit is started, and released when
it is stopped. The user ID is allocated from the range 61184..65519. The user
will not be added to /etc/passwd (but an NSS module to be added later should
make it show up in getent passwd).
For now, care should be taken that the service writes no files to disk, since
this might result in files owned by UIDs that might get assigned dynamically to
a different service later on. Later patches will tighten sandboxing in order to
ensure that this cannot happen, except for a few selected directories.
A simple way to test this is:
systemd-run -p DynamicUser=1 /bin/sleep 99999
This patch renames Read{Write,Only}Directories= and InaccessibleDirectories=
to Read{Write,Only}Paths= and InaccessiblePaths=, previous names are kept
as aliases but they are not advertised in the documentation.
Renamed variables:
`read_write_dirs` --> `read_write_paths`
`read_only_dirs` --> `read_only_paths`
`inaccessible_dirs` --> `inaccessible_paths`
Despite the name, `Read{Write,Only}Directories=` already allows for
regular file paths to be masked. This commit adds the same behavior
to `InaccessibleDirectories=` and makes it explicit in the doc.
This patch introduces `/run/systemd/inaccessible/{reg,dir,chr,blk,fifo,sock}`
{dile,device}nodes and mounts on the appropriate one the paths specified
in `InacessibleDirectories=`.
Based on Luca's patch from https://github.com/systemd/systemd/pull/3327
This permits services to detect whether their stdout/stderr is connected to the
journal, and if so talk to the journal directly, thus permitting carrying of
metadata.
As requested by the gtk folks: #2473
This adds three new seccomp syscall groups: @keyring for kernel keyring access,
@cpu-emulation for CPU emulation features, for exampe vm86() for dosemu and
suchlike, and @debug for ptrace() and related calls.
Also, the @clock group is updated with more syscalls that alter the system
clock. capset() is added to @privileged, and pciconfig_iobase() is added to
@raw-io.
Finally, @obsolete is a cleaned up. A number of syscalls that never existed on
Linux and have no number assigned on any architecture are removed, as they only
exist in the man pages and other operating sytems, but not in code at all.
create_module() is moved from @module to @obsolete, as it is an obsolete system
call. mem_getpolicy() is removed from the @obsolete list, as it is not
obsolete, but simply a NUMA API.
This patch implements the new magic character '!'. By putting '!' in front
of a command, systemd executes it with full privileges ignoring paramters
such as User, Group, SupplementaryGroups, CapabilityBoundingSet,
AmbientCapabilities, SecureBits, SystemCallFilter, SELinuxContext,
AppArmorProfile, SmackProcessLabel, and RestrictAddressFamilies.
Fixes partially https://github.com/systemd/systemd/issues/3414
Related to https://github.com/coreos/rkt/issues/2482
Testing:
1. Create a user 'bob'
2. Create the unit file /etc/systemd/system/exec-perm.service
(You can use the example below)
3. sudo systemctl start ext-perm.service
4. Verify that the commands starting with '!' were not executed as bob,
4.1 Looking to the output of ls -l /tmp/exec-perm
4.2 Each file contains the result of the id command.
`````````````````````````````````````````````````````````````````
[Unit]
Description=ext-perm
[Service]
Type=oneshot
TimeoutStartSec=0
User=bob
ExecStartPre=!/usr/bin/sh -c "/usr/bin/rm /tmp/exec-perm*" ;
/usr/bin/sh -c "/usr/bin/id > /tmp/exec-perm-start-pre"
ExecStart=/usr/bin/sh -c "/usr/bin/id > /tmp/exec-perm-start" ;
!/usr/bin/sh -c "/usr/bin/id > /tmp/exec-perm-star-2"
ExecStartPost=/usr/bin/sh -c "/usr/bin/id > /tmp/exec-perm-start-post"
ExecReload=/usr/bin/sh -c "/usr/bin/id > /tmp/exec-perm-reload"
ExecStop=!/usr/bin/sh -c "/usr/bin/id > /tmp/exec-perm-stop"
ExecStopPost=/usr/bin/sh -c "/usr/bin/id > /tmp/exec-perm-stop-post"
[Install]
WantedBy=multi-user.target]
`````````````````````````````````````````````````````````````````
New exec boolean MemoryDenyWriteExecute, when set, installs
a seccomp filter to reject mmap(2) with PAGE_WRITE|PAGE_EXEC
and mprotect(2) with PAGE_EXEC.
Definitions of ReadWriteDirectories=, ReadOnlyDirectories=, InaccessibleDirectories=,
WorkingDirectory=, and RootDirecory= were not clear. This patch specifies when
they are relative to the host's root directory and when they are relative to the service's
root directory.
Fixes#3248
Private /dev will not be managed by udev or others, so we can make it
noexec and readonly after we have made all device nodes. As /dev/shm
needs to be writable, we can't use bind_remount_recursive().
The manpage of seccomp specify that using seccomp with
SECCOMP_SET_MODE_FILTER will return EACCES if the caller do not have
CAP_SYS_ADMIN set, or if the no_new_privileges bit is not set. Hence,
without NoNewPrivilege set, it is impossible to use a SystemCall*
directive with a User directive set in system mode.
Now, NoNewPrivileges is set if we are in user mode, or if we are in
system mode and we don't have CAP_SYS_ADMIN, and SystemCall*
directives are used.
