.TH MINIJAIL0 "1" "July 2011" "Chromium OS" "User Commands"
.SH NAME
minijail0 \- sandbox a process
.SH DESCRIPTION
.PP
Runs PROGRAM inside a sandbox. See minijail(1) for details.
.SH EXAMPLES

Safely switch from root to nobody while dropping all capabilities and
inheriting any groups from nobody:

  # minijail0 -c 0 -G -u nobody /usr/bin/whoami
  nobody

Run in a PID and VFS namespace without superuser capabilities (but still
as root) and with a private view of /proc:

  # minijail0 -p -v -r -c 0 /bin/ps
    PID TTY           TIME CMD
      1 pts/0     00:00:00 minijail0
      2 pts/0     00:00:00 ps

Running a process with a seccomp filter policy at reduced privileges:

  # minijail0 -S /usr/share/minijail0/$(uname -m)/cat.policy -- \\
              /bin/cat /proc/self/seccomp_filter
  ...

.SH SECCOMP_FILTER POLICY
The policy file supplied to the \fB-S\fR argument supports the following syntax:

  \fB<syscall_name>\fR:\fB<ftrace filter policy>\fR
  \fB<syscall_number>\fR:\fB<ftrace filter policy>\fR
  \fB<empty line>\fR
  \fB# any single line comment\fR

A policy that emulates seccomp(2) in mode 1 may look like:
  read: 1
  write: 1
  sig_return: 1
  exit: 1

The "1" acts as a wildcard and allows any use of the mentioned system
call.  More advanced filtering is possible if your kernel supports
CONFIG_FTRACE_SYSCALLS.  For example, we can allow a process to open any
file read only and mmap PROT_READ only:

  # open with O_LARGEFILE|O_RDONLY|O_NONBLOCK or some combination
  open: flags == 32768 || flags == 0 || flags == 34816 || flags == 2048
  mmap2: prot == 0x0
  munmap: 1
  close: 1

The supported arguments may be found by reviewing the system call
prototypes in the Linux kernel source code.  Be aware that any
non-numeric comparison may be subject to time-of-check-time-of-use
attacks and cannot be considered safe.

\fBexecve\fR may only be used when invoking with CAP_SYS_ADMIN privileges.

.SH SECCOMP_FILTER POLICY WRITING

Determining policy for seccomp_filter can be time consuming.  System
calls are often named in arch-specific, or legacy tainted, ways.  E.g.,
geteuid versus geteuid32.  On process death due to a seccomp filter
rule, the offending system call number will be supplied with a best
guess of the ABI defined name.  This information may be used to produce
working baseline policies.  However, if the process being contained has
a fairly tight working domain, using \fBstrace -e raw=all <program>\fR
can generate the list of system calls that are needed. Note that when
using libminijail or minijail with preloading, supporting initial
process setup calls will not be required.  Be conservative.

It's also possible to analyze the binary checking for all non-dead
functions and determining if any of them issue system calls.  There is
no active implementation for this, but something like
code.google.com/p/seccompsandbox is one possible runtime variant.

.SH AUTHOR
The Chromium OS Authors <chromiumos-dev@chromium.org>
.SH COPYRIGHT
Copyright \(co 2011 The Chromium OS Authors
License BSD-like.
.SH "SEE ALSO"
\fBminijail\fR(1)