Also, move prlimit64() out of @resources.
prlimit64() may be used both for getting and setting resource limits, and
is implicitly called by glibc at various places, on some archs, the same
was as getrlimit(). SImilar, igetrlimit() is an arch-specific
replacement for getrlimit(), and hence should be whitelisted at the same
place as getrlimit() and prlimit64().
Also see: https://lists.freedesktop.org/archives/systemd-devel/2017-September/039543.html
This removes the '@credentials' syscall set that was added in commit
v234-468-gcd0ddf6f75.
Most of these syscalls are so simple that we do not want to filter them.
They work on the current calling process, doing only read operations,
they do not have a deep kernel path.
The problem may only be in 'capget' syscall since it can query arbitrary
processes, and used to discover processes, however sending signal 0 to
arbitrary processes can be used to discover if a process exists or not.
It is unfortunate that Linux allows to query processes of different
users. Lets put it now in '@process' syscall set, and later we may add
it to a new '@basic-process' set that allows most basic process
operations.
Given that sched_setattr/sched_setparam/sched_setscheduler are already
in the group the closely related nice + ioprio_set should also be
included.
Also, order things alphabetically.
Include the waid syscalls. If we permit forking then we should also
permit waiting for a process.
Similar to that: also permit determining the usage counters for
processes.
Include calls to determine process/thread identity. They have little
impact security-wise, but are very likely used when process management
of any form is done.
Also, add rt_sigqueueinfo + rt_tgsigqueueinfo as they are similar to
kill() and friends, but permit passing along a userdata ptr.
Let's add fremovexattr which was the only xattr syscall so far missing
from the group, even though lremovexattr and friends where included.
Add inotify_init, which is an older (but still supported) version of
inotify_init1.
Add oldfstat, oldlstat, oldstat which are old versions of the stat
syscalls on some archs.
Add utime, which is an older more limited version of utimes and
utimensat.
Enclose the "statx" entry in some ifdeffery to ensure libseccomp
actually knows the syscall. If libseccomp doesn't know it, then we'd get
EINVAL rather than EDOM (which is what is returned if a syscall is known
but not available on the local system) when resolving the syscall name
and we really don't want that, as we use the EDOM vs. EINVAL check for
determining whether a syscall makes sense at all.
Also, order things alphabetically.
Let's add _llseek which is the syscall name on some archs that on others
is simply lseek (due to 64bit vs 32bit off_t confusion). Also, let's
sort things alphabetically.
Let's add more of the most basic operations to "@default" as absolute
baseline needed by glibc and such to operate. Specifically:
futex, get_robust_list, get_thread_area, membarrier, set_robust_list,
set_thread_area, set_tid_address are all required to properly implement
mutexes and other thread synchronization logic. Given that a ton of
datastructures are protected by mutexes (such as stdio and such), let's
just whitelist this by default, so that things can just work.
restart_syscall is used to implement EAGAIN SA_RESTART stuff in some
archs, and synthesized by the kernel without any explicit user logic,
hence let's make this work out of the box.
Now that we have ported nspawn's seccomp code to the generic code in
seccomp-util, let's extend it to support whitelisting and blacklisting
of specific additional syscalls.
This uses similar syntax as PID1's support for system call filtering,
but in contrast to that always implements a blacklist (and not a
whitelist), as we prepopulate the filter with a blacklist, and the
unit's system call filter logic does not come with anything
prepopulated.
(Later on we might actually want to invert the logic here, and
whitelist rather than blacklist things, but at this point let's not do
that. In case we switch this over later, the syscall add/remove logic of
this commit should be compatible conceptually.)
Fixes: #5163
Replaces: #5944
Let's add a new helper function seccomp_add_syscall_filter_item() that
contains the inner loop code of seccomp_add_syscall_filter_set(). This
helper function we can then export and make use of elsewhere.
Add LockPersonality boolean to allow locking down personality(2)
system call so that the execution domain can't be changed.
This may be useful to improve security because odd emulations
may be poorly tested and source of vulnerabilities, while
system services shouldn't need any weird personalities.
This patch adds two new special character prefixes to ExecStart= and
friends, in addition to the existing "-", "@" and "+":
"!" → much like "+", except with a much reduced effect as it only
disables the actual setresuid()/setresgid()/setgroups() calls, but
leaves all other security features on, including namespace
options. This is very useful in combination with
RuntimeDirectory= or DynamicUser= and similar option, as a user
is still allocated and used for the runtime directory, but the
actual UID/GID dropping is left to the daemon process itself.
This should make RuntimeDirectory= a lot more useful for daemons
which insist on doing their own privilege dropping.
"!!" → Similar to "!", but on systems supporting ambient caps this
becomes a NOP. This makes it relatively straightforward to write
unit files that make use of ambient capabilities to let systemd
drop all privs while retaining compatibility with systems that
lack ambient caps, where priv dropping is the left to the daemon
codes themselves.
This is an alternative approach to #6564 and related PRs.
This new group lists all UID/GID credential changing syscalls (which are
quite a number these days). This will become particularly useful in a
later commit, which uses this group to optionally permit user credential
changing to daemons in case ambient capabilities are not available.
I messed up when adding the definitions in 4278d1f531.
Unfortunately I didn't have the hardware at hand and went by
looking at the kernel headers.
(cherry picked from commit 53196fafcb7b24b45ed4f48ab894d00a24a6d871)
"Failed to add rule for system call access, ignoring: Numerical argument out of domain"
is confusing. Make that "... system call access() / 238".
(cherry picked from commit 977dc6ca5acb8069a2966ec63e7378576bc2ca51)
We expect that if socket() syscall is available, seccomp works for that
architecture. So instead of explicitly listing all architectures where we know
it is not available, just assume it is broken if the number is not defined.
This should have the same effect, except that other architectures where it is
also broken will pass tests without further changes. (Architectures where the
filter should work, but does not work because of missing entries in
seccomp-util.c, will still fail.)
i386, s390, s390x are the exception — setting the filter fails, even though
socket() is available, so it needs to be special-cased
(https://github.com/systemd/systemd/issues/5215#issuecomment-277241488).
This remove the last define in seccomp-util.h that was only used in test-seccomp.c. Porting
the seccomp filter to new architectures should be simpler because now only two places need
to be modified.
RestrictAddressFamilies seems to work on ppc64[bl]e, so enable it (the tests pass).
While adding the defines for arm, I realized that we have pretty much all
known architectures covered, so SECCOMP_RESTRICT_NAMESPACES_BROKEN is not
necessary anymore. clone(2) is adamant that the order of the first two
arguments is only reversed on s390/s390x. So let's simplify things and remove
the #if.
Also updates the documentation and adds a mention of ppc64 support
which was enabled by #5325.
Tested on Debian mipsel and mips64el. The other 4 mips architectures
should have an identical user <-> kernel ABI to one of the 2 tested
systems.
Add a bit of code that tries to get the right parameter order in place
for some of the better known architectures, and skips
restrict_namespaces for other archs.
This also bypasses the test on archs where we don't know the right
order.
In this case I didn't bother with testing the case where no filter is
applied, since that is hopefully just an issue for now, as there's
nothing stopping us from supporting more archs, we just need to know
which order is right.
Fixes: #5241
On i386 we block the old mmap() call entirely, since we cannot properly
filter it. Thankfully it hasn't been used by glibc since quite some
time.
Fixes: #5240
https://github.com/systemd/systemd/issues/5215#issuecomment-277156262
libseccomp does not allow you to add architectures to a filter that
doesn't match the byte ordering of the architectures already added to
the filter (it would be a mess, not to mention largely pointless) and
since systemd attempts to add an ABI before removing the default native
ABI, you will always fail on Power (either due to ppc or ppc64le). The
fix is to remove the native ABI before adding a new ABI so you don't run
into problems with byte ordering.
You would likely see the same failure on a MIPS system.
Thanks @pcmoore!
This substantially reworks the seccomp code, to ensure better
compatibility with some architectures, including i386.
So far we relied on libseccomp's internal handling of the multiple
syscall ABIs supported on Linux. This is problematic however, as it does
not define clear semantics if an ABI is not able to support specific
seccomp rules we install.
This rework hence changes a couple of things:
- We no longer use seccomp_rule_add(), but only
seccomp_rule_add_exact(), and fail the installation of a filter if the
architecture doesn't support it.
- We no longer rely on adding multiple syscall architectures to a single filter,
but instead install a separate filter for each syscall architecture
supported. This way, we can install a strict filter for x86-64, while
permitting a less strict filter for i386.
- All high-level filter additions are now moved from execute.c to
seccomp-util.c, so that we can test them independently of the service
execution logic.
- Tests have been added for all types of our seccomp filters.
- SystemCallFilters= and SystemCallArchitectures= are now implemented in
independent filters and installation logic, as they semantically are
very much independent of each other.
Fixes: #4575
@filesystem groups various file system operations, such as opening files and
directories for read/write and stat()ing them, plus renaming, deleting,
symlinking, hardlinking.
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.
@resources contains various syscalls that alter resource limits and memory and
scheduling parameters of processes. As such they are good candidates to block
for most services.
@basic-io contains a number of basic syscalls for I/O, similar to the list
seccomp v1 permitted but slightly more complete. It should be useful for
building basic whitelisting for minimal sandboxes
The system call is already part in @default hence implicitly allowed anyway.
Also, if it is actually blocked then systemd couldn't execute the service in
question anymore, since the application of seccomp is immediately followed by
it.
