isolate.1.txt

ISOLATE(1)
==========

NAME
----
isolate - Isolate a process using Linux Containers

SYNOPSIS
--------
*isolate* 'options' *--init*

*isolate* 'options' *--run* +--+ 'program' 'arguments'

*isolate* 'options' *--cleanup*

DESCRIPTION
-----------
Run 'program' within a sandbox, so that it cannot communicate with the
outside world and its resource consumption is limited. This can be used
for example in a programming contest to run untrusted programs submitted
by contestants in a controlled environment.

The sandbox is used in the following way:

* Run *isolate --init*, which initializes the sandbox, creates its working directory and
prints its name to the standard output. Fails if the sandbox already existed.

* Populate the directory with the executable file of the program and its
input files.

* Call *isolate --run* to run the program. A single line describing the
status of the program is written to the standard error stream.

* Fetch the output of the program from the directory.

* Run *isolate --cleanup* to remove temporary files. Does nothing if the sandbox
was already cleaned up.

Please note that by default, the program is not allowed to start multiple
processes of threads. If you need that, turn on the control group mode
(see below).

OPTIONS
-------
*-M, --meta=*'file'::
	Output meta-data on the execution of the program to a given file.
	See below for syntax of the meta-files.

*-m, --mem=*'size'::
	Limit address space of the program to 'size' kilobytes. If more processes
	are allowed, this applies to each of them separately.

*-t, --time=*'time'::
	Limit run time of the program to 'time' seconds. Fractional numbers are allowed.
	Time in which the OS assigns the processor to different tasks is not counted.

*-w, --wall-time=*'time'::
	Limit wall-clock time to 'time' seconds. Fractional values are allowed.
	This clock measures the time from the start of the program to its exit,
	so it does not stop when the program has lost the CPU or when it is waiting
	for an external event. We recommend to use *--time* as the main limit,
	but set *--wall-time* to a much higher value as a precaution against
	sleeping programs.

*-x, --extra-time=*'time'::
	When a time limit is exceeded, wait for extra 'time' seconds before
	killing the program. This has the advantage that the real execution time
	is reported, even though it slightly exceeds the limit. Fractional
	numbers are again allowed.

*-b, --box-id=*'id'::
	When you run multiple sandboxes in parallel, you have to assign each unique
	IDs to them by this option. See the discussion on UIDs in the INSTALLATION
	section. The ID defaults to 0.

*-k, --stack=*'size'::
	Limit process stack to 'size' kilobytes. By default, the whole address
	space is available for the stack, but it is subject to the *--mem* limit.

*-f, --fsize=*'size'::
	Limit size of files created (or modified) by the program to 'size' kilobytes.
	In most cases, it is better to restrict overall disk usage by a disk quota
	(see below). This option can help in cases when quotas are not enabled
	on the underlying filesystem.

*-q, --quota=*'blocks'*,*'inodes'::
	Set disk quota to a given number of blocks and inodes. This requires the
	filesystem to be mounted with support for quotas. Please note that this
	currently works only on the ext family of filesystems (other filesystems
	use other interfaces for setting quotas).

*-i, --stdin=*'file'::
	Redirect standard input from 'file'. The 'file' has to be accessible
	inside the sandbox. Otherwise, standard input is inherited from the
	parent process.

*-o, --stdout=*'file'::
	Redirect standard output to 'file'. The 'file' has to be accessible
	inside the sandbox. Otherwise, standard output is inherited from the
	parent process and the sandbox manager does not write anything to it.

*-r, --stderr=*'file'::
	Redirect standard error output to 'file'. The 'file' has to be accessible
	inside the sandbox. Otherwise, standard error output is inherited from the
	parent process. See also *--stderr-to-stdout*.

*--stderr-to-stdout*::
	Redirect standard error output to standard output. This is performed after
	the standard output is redirected by *--stdout*. Mutually exclusive with *--stderr*.

*-c, --chdir=*'dir'::
	Change directory to 'dir' before executing the program. This path must be
	relative to the root of the sandbox.

*-p, --processes*[*=*'max']::
	Permit the program to create up to 'max' processes and/or threads. Please
	keep in mind that time and memory limit do not work with multiple processes
	unless you enable the control group mode. If 'max' is not given, an arbitrary
	number of processes can be run. By default, only one process is permitted.

*--share-net*::
	By default, isolate creates a new network namespace for its child process.
	This namespace contains no network devices except for a per-namespace loopback.
	This prevents the program from communicating with the outside world. If you want
	to permit communication, you can use this switch to keep the child process
	in parent's network namespace.

*--inherit-fds*::
	By default, isolate closes all file descriptors passed from its parent
	except for descriptors 0, 1, and 2.
	This prevents unintentional descriptor leaks. In some cases, passing extra
	descriptors to the sandbox can be desirable, so you can use this switch
	to make them survive.

*-v, --verbose*::
	Tell the sandbox manager to be verbose and report on what is going on.
	Using *-v* multiple times produces even more jabber.

*-s, --silent*::
	Tell the sandbox manager to keep silence. No status messages are printed
	to stderr except for fatal errors of the sandbox itself. The combination of
	*--verbose* and *--silent* has an undefined effect.

*--tty-hack*::
	Try to handle interactive programs communicating over a tty.
	The sandboxed program will run in a separate process group, which will temporarily
	become the foreground process group of the terminal. When the program exits, the
	process group will be switched back to the caller. Please note that the program
	can do many nasty things including (but not limited to) changing terminal settings,
	changing the line discipline, and stuffing characters to the terminal's input queue
	using the TIOCSTI ioctl. Use with extreme caution.

ENVIRONMENT RULES
-----------------
UNIX processes normally inherit all environment variables from their parent. The
sandbox however passes only those variables which are explicitly requested by
environment rules:

*-E, --env=*'var'::
	Inherit the variable 'var' from the parent.

*-E, --env=*'var'*=*'value'::
	Set the variable 'var' to 'value'. When the 'value' is empty, the
	variable is removed from the environment.

*-e, --full-env*::
	Inherit all variables from the parent.

The rules are applied in the order in which they were given, except for
*--full-env*, which is applied first.

The list of rules is automatically initialized with *-ELIBC_FATAL_STDERR_=1*.

DIRECTORY RULES
---------------
The sandboxed process gets its own filesystem namespace, which contains only subtrees
requested by directory rules:

*-d, --dir=*'in'*=*'out'[*:*'options']::
	Bind the directory 'out' as seen by the caller to the path 'in' inside the sandbox.
	If there already was a directory rule for 'in', it is replaced.

*-d, --dir=*'dir'[*:*'options']::
	Bind the directory +/+'dir' to 'dir' inside the sandbox.
	If there already was a directory rule for 'in', it is replaced.

*-d, --dir=*'in'*=*::
	Remove a directory rule for the path 'in' inside the sandbox.

By default, all directories are bound read-only and restricted (no devices,
no setuid binaries). This behavior can be modified using the 'options':

*rw*::
	Allow read-write access.

*dev*::
	Allow access to character and block devices.

*noexec*::
	Disallow execution of binaries.

*maybe*::
	Silently ignore the rule if the directory to be bound does not exist.

*fs*::
	Instead of binding a directory, mount a device-less filesystem called 'in'.
	For example, this can be 'proc' or 'sysfs'.

*tmp*::
	Bind a freshly created temporary directory writeable for the sandbox user.
	Accepts no 'out', implies *rw*.

*norec*::
	Do not bind recursively. Without this option, mount points in the outside
	directory tree are automatically propagated to the sandbox.

Unless *--no-default-dirs* is specified, the default set of directory rules binds +/bin+,
+/dev+ (with devices allowed), +/lib+, +/lib64+ (if it exists), and +/usr+. It also binds
the working directory to +/box+ (read-write), mounts the proc filesystem at +/proc+, and
creates a temporary directory +/tmp+.

*-D, --no-default-dirs*::
	Do not bind the default set of directories. Care has to be taken to specify
	the correct set of rules (using *--dir*) for the executed program to run
	correctly. In particular, +/box+ has to be bound.

The rules are executed in the order in which they are given. Default rules come before
all user rules. When a rule is replaced, it retains the original position
in the order. This matters when one rule's 'in' is a sub-directory of another
rule's 'in'. For example if you first bind to 'a' and then to 'a/b', it will work as
expected, but a sub-directory 'b' must have existed in the directory bound to 'a' (isolate
never creates subdirectories in bound directories for security reasons). If the
order is 'a/b' before 'a', then the directory bound to 'a/b' becomes invisible
by the later binding on 'a'.

CONTROL GROUPS
--------------
Isolate can make use of system control groups provided by the kernel
to constrain programs consisting of multiple processes. Please note
that this feature needs special system setup described in the INSTALLATION
section.

*--cg*::
	Enable use of control groups. This should be specified with *--init*,
	*--run* and *--cleanup*.

*--cg-mem=*'size'::
	Limit total memory usage by the whole control group to 'size' kilobytes.
	This should be specified with *--run*.

*--cg-timing*::
	Use control groups for timing, so that the *--time* switch affects the
	total run time of all processes and threads in the control group.
	This should be specified with *--run*.
	This option is turned on by default, use *--no-cg-timing* to turn off.

META-FILES
----------
The meta-file contains miscellaneous meta-information on execution of the
program within the sandbox. It is a textual file consisting of lines
of format 'key'*:*'value'. The following keys are defined:

*cg-mem*::
	When control groups are enabled, this is the total memory use
	by the whole control group (in kilobytes).
*cg-oom-killed*::
	Present when the program was killed by the out-of-memory killer
	(e.g., because it has exceeded the memory limit of its control group).
	This is reported only on Linux 4.13 and later.
*csw-forced*::
	Number of context switches forced by the kernel.
*csw-voluntary*::
	Number of context switches caused by the process giving up the CPU
	voluntarily.
*exitcode*::
	The program has exited normally with this exit code.
*exitsig*::
	The program has exited after receiving this fatal signal.
*killed*::
	Present when the program was terminated by the sandbox
	(e.g., because it has exceeded the time limit).
*max-rss*::
	Maximum resident set size of the process (in kilobytes).
*message*::
	Status message, not intended for machine processing.
	E.g., "Time limit exceeded."
*status*::
	Two-letter status code:
	* *RE* -- run-time error, i.e., exited with a non-zero exit code
	* *SG* -- program died on a signal
	* *TO* -- timed out
	* *XX* -- internal error of the sandbox
*time*::
	Run time of the program in fractional seconds.
*time-wall*::
	Wall clock time of the program in fractional seconds.

Please note that not all keys have to be present.
For example, no *status* nor *message* is reported upon normal termination.

RETURN VALUE
------------
When the program inside the sandbox finishes correctly, the sandbox returns 0.
If it finishes incorrectly, it returns 1.
All other return codes signal an internal error.

INSTALLATION
------------
Isolate depends on several advanced features of the Linux kernel. Please
make sure that your kernel supports
PID namespaces (+CONFIG_PID_NS+),
IPC namespaces (+CONFIG_IPC_NS+), and
network namespaces (+CONFIG_NET_NS+).
If you want to use control groups, you need
the cpusets (+CONFIG_CPUSETS+),
CPU accounting controller (+CONFIG_CGROUP_CPUACCT+), and
memory resource controller (+CONFIG_MEMCG+). If your machine has swap enabled,
you should also enable the swap controller (+CONFIG_MEMCG_SWAP+).

Debian 7.x and newer require enabling the memory and swap cgroup controllers by
adding the parameters "cgroup_enable=memory swapaccount=1" to the kernel
command-line, which can be set using +GRUB_CMDLINE_LINUX_DEFAULT+ in
/etc/default/grub.

Isolate is designed to run setuid to root. The sub-process inside the sandbox
then switches to a non-privileged user ID (different for each *--box-id*).
The range of UIDs available and several filesystem paths are set in a configuration
file, by default located in /usr/local/etc/isolate.

Before you run isolate with control groups, you need to ensure that the cgroup
filesystem is enabled and mounted.  Most modern Linux distributions already
provide cgroup support through a tmpfs mounted at /sys/fs/cgroup, with
individual controllers mounted within subdirectories.

Isolate expects that the root directory "/" is a mount point. When running
isolate inside a chroot, this may not be the case, and isolate may fail with
"Cannot privatize mounts". A workaround for this is to convert the root
directory of the chroot into a mount point using a bind mount, prior to
entering the chroot and running isolate. For example:

    mount --bind /path/to/chroot /path/to/chroot

REPRODUCIBILITY
---------------

The reproducibility of results can be improved by tuning some kernel
parameters, listed below. Some of these parameters can be checked using the
program isolate-check-environment.

* Disable address space randomization: +sysctl kernel.randomize_va_space=0+.
Address space randomization can affect timing, memory usage, and program
behavior. This setting can be made persistent through /etc/sysctl.d/.

* Disable dynamic CPU frequency scaling. This requires setting the cpufreq
scaling governor to +performance+. The process for doing this varies between
distributions.

* Consider disabling Turboboost on CPUs that might support it (most i3/i5/i7
Intel CPUs). Approach this one with caution. Disabling a CPU that Turboboosts
from 2.3 GHz to 2.6 GHz would have minimal impact on run-times in exchange
for determinism, but the same on a CPU that Turboboosts from 1.6 GHz to 2.8
GHz will incur a much more dramatic slowdown. Perhaps if the ambient
temperature is controlled and only one single-threaded task is keeping the
CPU busy at 100%, then TB's behaviour may be reasonably deterministic;
requires further experimentation to confirm.

* Run evaluations on a single CPU (core). The Linux scheduler has a tendency to randomly
migrate tasks between CPUs, incurring cache migration costs. You can use isolate's
configuration file to pin the process to a specified CPU.

* Disable automatic kernel support for transparent huge pages. Both /sys/kernel/mm/transparent_hugepage/enabled
and /sys/kernel/mm/transparent_hugepage/defrag should be set to "madvise" or "never", and
/sys/kernel/mm/transparent_hugepage/khugepaged/defrag to 0.

* Disable swapping. If you really need swap space and you are using cgroups,
make sure that you have the memsw controller enabled, so that swap space is
properly accounted for.

LICENSE
-------
Isolate was written by Martin Mares and Bernard Blackham.
It can be distributed and used under the terms of the GNU
General Public License version 2 or any later version.