In #22554 I aligned seccomp and capabilities, however the case of
the chown calls and CAP_CHOWN was less clearcut, as these are
simple calls that the capabilities will block if they are not
allowed. They are needed when no new privileges is not set in
order to allow docker to call chown before the container is
started, so there was a workaround but this did not include
all the chown syscalls, and Arm was failing on some seccomp
tests because it was using a different syscall from just the
fchown that was allowed in this case. It is simpler to just
allow all the chown calls in the default seccomp profile and
let the capabilities subsystem block them.
Signed-off-by: Justin Cormack <justin.cormack@docker.com>
In order to do this, allow the socketcall syscall in the default
seccomp profile. This is a multiplexing syscall for the socket
operations, which is becoming obsolete gradually, but it is used
in some architectures. libseccomp has special handling for it for
x86 where it is common, so we did not need it in the profile,
but does not have any handling for ppc64le. It turns out that the
Debian images we use for tests do use the socketcall, while the
newer images such as Ubuntu 16.04 do not. Enabling this does no
harm as we allow all the socket operations anyway, and we allow
the similar ipc call for similar reasons already.
Signed-off-by: Justin Cormack <justin.cormack@docker.com>
Currently the default seccomp profile is fixed. This changes it
so that it varies depending on the Linux capabilities selected with
the --cap-add and --cap-drop options. Without this, if a user adds
privileges, eg to allow ptrace with --cap-add sys_ptrace then still
cannot actually use ptrace as it is still blocked by seccomp, so
they will probably disable seccomp or use --privileged. With this
change the syscalls that are needed for the capability are also
allowed by the seccomp profile based on the selected capabilities.
While this patch makes it easier to do things with for example
cap_sys_admin enabled, as it will now allow creating new namespaces
and use of mount, it still allows less than --cap-add cap_sys_admin
--security-opt seccomp:unconfined would have previously. It is not
recommended that users run containers with cap_sys_admin as this does
give full access to the host machine.
It also cleans up some architecture specific system calls to be
only selected when needed.
Signed-off-by: Justin Cormack <justin.cormack@docker.com>
These syscalls are already blocked by the default capabilities:
mlock mlock2 mlockall require CAP_IPC_LOCK
vhangup requires CAP_SYS_TTY_CONFIG
There is therefore no reason to allow them in the default profile
as they cannot be used anyway.
Signed-off-by: Justin Cormack <justin.cormack@docker.com>
This adds the following new syscalls that are supported in libseccomp 2.3.0,
including calls added up to kernel 4.5-rc4:
mlock2 - same as mlock but with a flag
copy_file_range - copy file contents, like splice but with reflink support.
The following are not added, and mentioned in docs:
userfaultfd - userspace page fault handling, mainly designed for process migration
The following are not added, only apply to less common architectures:
switch_endian
membarrier
breakpoint
set_tls
I plan to review the other architectures, some of which can now have seccomp
enabled in the build as they are now supported.
Signed-off-by: Justin Cormack <justin.cormack@docker.com>
Fixes#20818
This syscall was blocked as there was some concern that it could be
used to bypass filtering of other syscall arguments. However none of the
potential syscalls where this could be an issue (poll, nanosleep,
clock_nanosleep, futex) are blocked in the default profile anyway.
Signed-off-by: Justin Cormack <justin.cormack@docker.com>
On 32 bit x86 this is a multiplexing syscall for the system V
ipc syscalls such as shmget, and so needs to be allowed for
shared memory access for 32 bit binaries.
Fixes#20733
Signed-off-by: Justin Cormack <justin.cormack@docker.com>
We generally want to filter the personality(2) syscall, as it
allows disabling ASLR, and turning on some poorly supported
emulations that have been the target of CVEs. However the use
cases for reading the current value, setting the default
PER_LINUX personality, and setting PER_LINUX32 for 32 bit
emulation are fine.
See issue #20634
Signed-off-by: Justin Cormack <justin.cormack@docker.com>
