githubmirror/libseccomp

src/python/seccomp.pyx
745 строк28 KB
Paul Moore
python: use Cython language "3str"
02 авг 2019, 21:04
02 авг 2019, 21:0474b4d5f
#
# Seccomp Library Python Bindings
#
# Copyright (c) 2012,2013,2017 Red Hat <pmoore@redhat.com>
# Author: Paul Moore <paul@paul-moore.com>
#

#
# This library is free software; you can redistribute it and/or modify it
# under the terms of version 2.1 of the GNU Lesser General Public License as
# published by the Free Software Foundation.
#
# This library is distributed in the hope that it will be useful, but WITHOUT
# ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
# FITNESS FOR A PARTICULAR PURPOSE.  See the GNU Lesser General Public License
# for more details.
#
# You should have received a copy of the GNU Lesser General Public License
# along with this library; if not, see <http://www.gnu.org/licenses>.
#

# cython: language_level = 3str

""" Python bindings for the libseccomp library

The libseccomp library provides and easy to use, platform independent,
interface to the Linux Kernel's syscall filtering mechanism: seccomp.  The
libseccomp API is designed to abstract away the underlying BPF based
syscall filter language and present a more conventional function-call
based filtering interface that should be familiar to, and easily adopted
by application developers.

Filter action values:
    KILL_PROCESS - kill the process
    KILL - kill the thread
    LOG - allow the syscall to be executed after the action has been logged
    ALLOW - allow the syscall to execute
    TRAP - a SIGSYS signal will be thrown
    ERRNO(x) - syscall will return (x)
    TRACE(x) - if the process is being traced, (x) will be returned to the
               tracing process via PTRACE_EVENT_SECCOMP and the
               PTRACE_GETEVENTMSG option

Argument comparison values (see the Arg class):

    NE - arg != datum_a
    LT - arg < datum_a
    LE - arg <= datum_a
    EQ - arg == datum_a
    GT - arg > datum_a
    GE - arg >= datum_a
    MASKED_EQ - (arg & datum_a) == datum_b


Example:

    import sys
    from seccomp import *

    # create a filter object with a default KILL action
    f = SyscallFilter(defaction=KILL)

    # add syscall filter rules to allow certain syscalls
    f.add_rule(ALLOW, "open")
    f.add_rule(ALLOW, "close")
    f.add_rule(ALLOW, "read", Arg(0, EQ, sys.stdin))
    f.add_rule(ALLOW, "write", Arg(0, EQ, sys.stdout))
    f.add_rule(ALLOW, "write", Arg(0, EQ, sys.stderr))
    f.add_rule(ALLOW, "rt_sigreturn")

    # load the filter into the kernel
    f.load()
"""
__author__ =  'Paul Moore <paul@paul-moore.com>'
__date__ = "3 February 2017"

from cpython.version cimport PY_MAJOR_VERSION
from libc.stdint cimport uint32_t
import errno

cimport libseccomp

def c_str(string):
    """ Convert a Python string to a C string.

    Arguments:
    string - the Python string

    Description:
    Convert the Python string into a form usable by C taking into consideration
    the Python major version, e.g. Python 2.x or Python 3.x.
    See http://docs.cython.org/en/latest/src/tutorial/strings.html for more
    information.
    """
    if PY_MAJOR_VERSION < 3:
        return string
    else:
        return bytes(string, "ascii")

KILL_PROCESS = libseccomp.SCMP_ACT_KILL_PROCESS
KILL = libseccomp.SCMP_ACT_KILL
TRAP = libseccomp.SCMP_ACT_TRAP
LOG = libseccomp.SCMP_ACT_LOG
ALLOW = libseccomp.SCMP_ACT_ALLOW
def ERRNO(int errno):
    """The action ERRNO(x) means that the syscall will return (x).
    To conform to Linux syscall calling conventions, the syscall return
    value should almost always be a negative number.
    """
    return libseccomp.SCMP_ACT_ERRNO(errno)
def TRACE(int value):
    """The action TRACE(x) means that, if the process is being traced, (x)
    will be returned to the tracing process via PTRACE_EVENT_SECCOMP
    and the PTRACE_GETEVENTMSG option.
    """
    return libseccomp.SCMP_ACT_TRACE(value)

NE = libseccomp.SCMP_CMP_NE
LT = libseccomp.SCMP_CMP_LT
LE = libseccomp.SCMP_CMP_LE
EQ = libseccomp.SCMP_CMP_EQ
GE = libseccomp.SCMP_CMP_GE
GT = libseccomp.SCMP_CMP_GT
MASKED_EQ = libseccomp.SCMP_CMP_MASKED_EQ

def system_arch():
    """ Return the system architecture value.

    Description:
    Returns the native system architecture value.
    """
    return libseccomp.seccomp_arch_native()

def resolve_syscall(arch, syscall):
    """ Resolve the syscall.

    Arguments:
    arch - the architecture value, e.g. Arch.*
    syscall - the syscall name or number

    Description:
    Resolve an architecture's syscall name to the correct number or the
    syscall number to the correct name.
    """
    cdef char *ret_str

    if isinstance(syscall, basestring):
        return libseccomp.seccomp_syscall_resolve_name_rewrite(arch,
                                                               c_str(syscall))
    elif isinstance(syscall, int):
        ret_str = libseccomp.seccomp_syscall_resolve_num_arch(arch, syscall)
        if ret_str is NULL:
            raise ValueError('Unknown syscall %d on arch %d' % (syscall, arch))
        else:
            return ret_str
    else:
        raise TypeError("Syscall must either be an int or str type")

def get_api():
    """ Query the level of API support

    Description:
    Returns the API level value indicating the current supported
    functionality.
    """
    level = libseccomp.seccomp_api_get()
    if level < 0:
        raise RuntimeError(str.format("Library error (errno = {0})", level))

    return level

def set_api(unsigned int level):
    """ Set the level of API support

    Arguments:
    level - the API level

    Description:
    This function forcibly sets the API level at runtime.  General use
    of this function is strongly discouraged.
    """
    rc = libseccomp.seccomp_api_set(level)
    if rc == -errno.EINVAL:
        raise ValueError("Invalid level")
    elif rc != 0:
        raise RuntimeError(str.format("Library error (errno = {0})", rc))

cdef class Arch:
    """ Python object representing the SyscallFilter architecture values.

    Data values:
    NATIVE - the native architecture
    X86 - 32-bit x86
    X86_64 - 64-bit x86
    X32 - 64-bit x86 using the x32 ABI
    ARM - ARM
    AARCH64 - 64-bit ARM
    MIPS - MIPS O32 ABI
    MIPS64 - MIPS 64-bit ABI
    MIPS64N32 - MIPS N32 ABI
    MIPSEL - MIPS little endian O32 ABI
    MIPSEL64 - MIPS little endian 64-bit ABI
    MIPSEL64N32 - MIPS little endian N32 ABI
    PARISC - 32-bit PA-RISC
    PARISC64 - 64-bit PA-RISC
    PPC64 - 64-bit PowerPC
    PPC - 32-bit PowerPC
    """

    cdef int _token

    NATIVE = libseccomp.SCMP_ARCH_NATIVE
    X86 = libseccomp.SCMP_ARCH_X86
    X86_64 = libseccomp.SCMP_ARCH_X86_64
    X32 = libseccomp.SCMP_ARCH_X32
    ARM = libseccomp.SCMP_ARCH_ARM
    AARCH64 = libseccomp.SCMP_ARCH_AARCH64
    MIPS = libseccomp.SCMP_ARCH_MIPS
    MIPS64 = libseccomp.SCMP_ARCH_MIPS64
    MIPS64N32 = libseccomp.SCMP_ARCH_MIPS64N32
    MIPSEL = libseccomp.SCMP_ARCH_MIPSEL
    MIPSEL64 = libseccomp.SCMP_ARCH_MIPSEL64
    MIPSEL64N32 = libseccomp.SCMP_ARCH_MIPSEL64N32
    PARISC = libseccomp.SCMP_ARCH_PARISC
    PARISC64 = libseccomp.SCMP_ARCH_PARISC64
    PPC = libseccomp.SCMP_ARCH_PPC
    PPC64 = libseccomp.SCMP_ARCH_PPC64
    PPC64LE = libseccomp.SCMP_ARCH_PPC64LE
    S390 = libseccomp.SCMP_ARCH_S390
    S390X = libseccomp.SCMP_ARCH_S390X

    def __cinit__(self, arch=libseccomp.SCMP_ARCH_NATIVE):
        """ Initialize the architecture object.

        Arguments:
        arch - the architecture name or token value

        Description:
        Create an architecture object using the given name or token value.
        """
        if isinstance(arch, int):
            if arch == libseccomp.SCMP_ARCH_NATIVE:
                self._token = libseccomp.seccomp_arch_native()
            elif arch == libseccomp.SCMP_ARCH_X86:
                self._token = libseccomp.SCMP_ARCH_X86
            elif arch == libseccomp.SCMP_ARCH_X86_64:
                self._token = libseccomp.SCMP_ARCH_X86_64
            elif arch == libseccomp.SCMP_ARCH_X32:
                self._token = libseccomp.SCMP_ARCH_X32
            elif arch == libseccomp.SCMP_ARCH_ARM:
                self._token = libseccomp.SCMP_ARCH_ARM
            elif arch == libseccomp.SCMP_ARCH_AARCH64:
                self._token = libseccomp.SCMP_ARCH_AARCH64
            elif arch == libseccomp.SCMP_ARCH_MIPS:
                self._token = libseccomp.SCMP_ARCH_MIPS
            elif arch == libseccomp.SCMP_ARCH_MIPS64:
                self._token = libseccomp.SCMP_ARCH_MIPS64
            elif arch == libseccomp.SCMP_ARCH_MIPS64N32:
                self._token = libseccomp.SCMP_ARCH_MIPS64N32
            elif arch == libseccomp.SCMP_ARCH_MIPSEL:
                self._token = libseccomp.SCMP_ARCH_MIPSEL
            elif arch == libseccomp.SCMP_ARCH_MIPSEL64:
                self._token = libseccomp.SCMP_ARCH_MIPSEL64
            elif arch == libseccomp.SCMP_ARCH_MIPSEL64N32:
                self._token = libseccomp.SCMP_ARCH_MIPSEL64N32
            elif arch == libseccomp.SCMP_ARCH_PARISC:
                self._token = libseccomp.SCMP_ARCH_PARISC
            elif arch == libseccomp.SCMP_ARCH_PARISC64:
                self._token = libseccomp.SCMP_ARCH_PARISC64
            elif arch == libseccomp.SCMP_ARCH_PPC:
                self._token = libseccomp.SCMP_ARCH_PPC
            elif arch == libseccomp.SCMP_ARCH_PPC64:
                self._token = libseccomp.SCMP_ARCH_PPC64
            elif arch == libseccomp.SCMP_ARCH_PPC64LE:
                self._token = libseccomp.SCMP_ARCH_PPC64LE
            elif arch == libseccomp.SCMP_ARCH_S390:
                self._token = libseccomp.SCMP_ARCH_S390
            elif arch == libseccomp.SCMP_ARCH_S390X:
                self._token = libseccomp.SCMP_ARCH_S390X
            else:
                self._token = 0;
        elif isinstance(arch, basestring):
            self._token = libseccomp.seccomp_arch_resolve_name(c_str(arch))
        else:
            raise TypeError("Architecture must be an int or str type")
        if self._token == 0:
            raise ValueError("Invalid architecture")

    def __int__(self):
        """ Convert the architecture object to a token value.

        Description:
        Convert the architecture object to an integer representing the
        architecture's token value.
        """
        return self._token

cdef class Attr:
    """ Python object representing the SyscallFilter attributes.

    Data values:
    ACT_DEFAULT - the filter's default action
    ACT_BADARCH - the filter's bad architecture action
    CTL_NNP - the filter's "no new privileges" flag
    CTL_NNP - the filter's thread sync flag
    """
    ACT_DEFAULT = libseccomp.SCMP_FLTATR_ACT_DEFAULT
    ACT_BADARCH = libseccomp.SCMP_FLTATR_ACT_BADARCH
    CTL_NNP = libseccomp.SCMP_FLTATR_CTL_NNP
    CTL_TSYNC = libseccomp.SCMP_FLTATR_CTL_TSYNC
    API_TSKIP = libseccomp.SCMP_FLTATR_API_TSKIP
    CTL_LOG = libseccomp.SCMP_FLTATR_CTL_LOG

cdef class Arg:
    """ Python object representing a SyscallFilter syscall argument.
    """
    cdef libseccomp.scmp_arg_cmp _arg

    def __cinit__(self, arg, op, datum_a, datum_b = 0):
        """ Initialize the argument comparison.

        Arguments:
        arg - the argument number, starting at 0
        op - the argument comparison operator, e.g. {NE,LT,LE,...}
        datum_a - argument value
        datum_b - argument value, only valid when op == MASKED_EQ

        Description:
        Create an argument comparison object for use with SyscallFilter.
        """
        self._arg.arg = arg
        self._arg.op = op
        self._arg.datum_a = datum_a
        self._arg.datum_b = datum_b

    cdef libseccomp.scmp_arg_cmp to_c(self):
        """ Convert the object into a C structure.

        Description:
        Helper function which should only be used internally by
        SyscallFilter objects and exists for the sole purpose of making it
        easier to deal with the varadic functions of the libseccomp API,
        e.g. seccomp_rule_add().
        """
        return self._arg

cdef class SyscallFilter:
    """ Python object representing a seccomp syscall filter. """
    cdef int _defaction
    cdef libseccomp.scmp_filter_ctx _ctx

    def __cinit__(self, int defaction):
        self._ctx = libseccomp.seccomp_init(defaction)
        if self._ctx == NULL:
            raise RuntimeError("Library error")
        _defaction = defaction

    def __init__(self, defaction):
        """ Initialize the filter state

        Arguments:
        defaction - the default filter action

        Description:
        Initializes the seccomp filter state to the defaults.
        """

    def __dealloc__(self):
        """ Destroys the filter state and releases any resources.

        Description:
        Destroys the seccomp filter state and releases any resources
        associated with the filter state.  This function does not affect
        any seccomp filters already loaded into the kernel.
        """
        if self._ctx != NULL:
            libseccomp.seccomp_release(self._ctx)

    def reset(self, int defaction = -1):
        """ Reset the filter state.

        Arguments:
        defaction - the default filter action

        Description:
        Resets the seccomp filter state to an initial default state, if a
        default filter action is not specified in the reset call the
        original action will be reused.  This function does not affect any
        seccomp filters alread loaded into the kernel.
        """
        if defaction == -1:
            defaction = self._defaction
        rc = libseccomp.seccomp_reset(self._ctx, defaction)
        if rc == -errno.EINVAL:
            raise ValueError("Invalid action")
        if rc != 0:
            raise RuntimeError(str.format("Library error (errno = {0})", rc))
        _defaction = defaction

    def merge(self, SyscallFilter filter):
        """ Merge two existing SyscallFilter objects.

        Arguments:
        filter - a valid SyscallFilter object

        Description:
        Merges a valid SyscallFilter object with the current SyscallFilter
        object; the passed filter object will be reset on success.  In
        order to successfully merge two seccomp filters they must have the
        same attribute values and not share any of the same architectures.
        """
        rc = libseccomp.seccomp_merge(self._ctx, filter._ctx)
        if rc != 0:
            raise RuntimeError(str.format("Library error (errno = {0})", rc))
        filter._ctx = NULL
        filter = SyscallFilter(filter._defaction)

    def exist_arch(self, arch):
        """ Check if the seccomp filter contains a given architecture.

        Arguments:
        arch - the architecture value, e.g. Arch.*

        Description:
        Test to see if a given architecture is included in the filter.
        Return True is the architecture exists, False if it does not
        exist.
        """
        rc = libseccomp.seccomp_arch_exist(self._ctx, arch)
        if rc == 0:
            return True
        elif rc == -errno.EEXIST:
            return False
        elif rc == -errno.EINVAL:
            raise ValueError("Invalid architecture")
        else:
            raise RuntimeError(str.format("Library error (errno = {0})", rc))

    def add_arch(self, arch):
        """ Add an architecture to the filter.

        Arguments:
        arch - the architecture value, e.g. Arch.*

        Description:
        Add the given architecture to the filter.  Any new rules added
        after this method returns successfully will be added to this new
        architecture, but any existing rules will not be added to the new
        architecture.
        """
        rc = libseccomp.seccomp_arch_add(self._ctx, arch)
        if rc == -errno.EINVAL:
            raise ValueError("Invalid architecture")
        elif rc != 0:
            raise RuntimeError(str.format("Library error (errno = {0})", rc))

    def remove_arch(self, arch):
        """ Remove an architecture from the filter.

        Arguments:
        arch - the architecture value, e.g. Arch.*

        Description:
        Remove the given architecture from the filter.  The filter must
        always contain at least one architecture, so if only one
        architecture exists in the filter this method will fail.
        """
        rc = libseccomp.seccomp_arch_remove(self._ctx, arch)
        if rc == -errno.EINVAL:
            raise ValueError("Invalid architecture")
        elif rc != 0:
            raise RuntimeError(str.format("Library error (errno = {0})", rc))

    def load(self):
        """ Load the filter into the Linux Kernel.

        Description:
        Load the current filter into the Linux Kernel.  As soon as the
        method returns the filter will be active and enforcing.
        """
        rc = libseccomp.seccomp_load(self._ctx)
        if rc != 0:
            raise RuntimeError(str.format("Library error (errno = {0})", rc))

    def get_attr(self, attr):
        """ Get an attribute value from the filter.

        Arguments:
        attr - the attribute, e.g. Attr.*

        Description:
        Lookup the given attribute in the filter and return the
        attribute's value to the caller.
        """
        cdef uint32_t value = 0
        rc = libseccomp.seccomp_attr_get(self._ctx,
                                         attr, <uint32_t *>&value)
        if rc == -errno.EINVAL:
            raise ValueError("Invalid attribute")
        elif rc != 0:
            raise RuntimeError(str.format("Library error (errno = {0})", rc))
        return value

    def set_attr(self, attr, int value):
        """ Set a filter attribute.

        Arguments:
        attr - the attribute, e.g. Attr.*
        value - the attribute value

        Description:
        Lookup the given attribute in the filter and assign it the given
        value.
        """
        rc = libseccomp.seccomp_attr_set(self._ctx, attr, value)
        if rc == -errno.EINVAL:
            raise ValueError("Invalid attribute")
        elif rc != 0:
            raise RuntimeError(str.format("Library error (errno = {0})", rc))

    def syscall_priority(self, syscall, int priority):
        """ Set the filter priority of a syscall.

        Arguments:
        syscall - the syscall name or number
        priority - the priority of the syscall

        Description:
        Set the filter priority of the given syscall.  A syscall with a
        higher priority will have less overhead in the generated filter
        code which is loaded into the system.  Priority values can range
        from 0 to 255 inclusive.
        """
        if priority < 0 or priority > 255:
            raise ValueError("Syscall priority must be between 0 and 255")
        if isinstance(syscall, str):
            syscall_str = syscall.encode()
            syscall_num = libseccomp.seccomp_syscall_resolve_name(syscall_str)
        elif isinstance(syscall, int):
            syscall_num = syscall
        else:
            raise TypeError("Syscall must either be an int or str type")
        rc = libseccomp.seccomp_syscall_priority(self._ctx,
                                                 syscall_num, priority)
        if rc != 0:
            raise RuntimeError(str.format("Library error (errno = {0})", rc))

    def add_rule(self, int action, syscall, *args):
        """ Add a new rule to filter.

        Arguments:
        action - the rule action: KILL_PROCESS, KILL, TRAP, ERRNO(), TRACE(),
                 LOG, or ALLOW
        syscall - the syscall name or number
        args - variable number of Arg objects

        Description:
        Add a new rule to the filter, matching on the given syscall and an
        optional list of argument comparisons.  If the rule is triggered
        the given action will be taken by the kernel.  In order for the
        rule to trigger, the syscall as well as each argument comparison
        must be true.

        In the case where the specific rule is not valid on a specific
        architecture, e.g. socket() on 32-bit x86, this method rewrites
        the rule to the best possible match.  If you don't want this fule
        rewriting to take place use add_rule_exactly().
        """
        cdef libseccomp.scmp_arg_cmp c_arg[6]
        if isinstance(syscall, str):
            syscall_str = syscall.encode()
            syscall_num = libseccomp.seccomp_syscall_resolve_name(syscall_str)
        elif isinstance(syscall, int):
            syscall_num = syscall
        else:
            raise TypeError("Syscall must either be an int or str type")
        """ NOTE: the code below exists solely to deal with the varadic
        nature of seccomp_rule_add() function and the inability of Cython
        to handle this automatically """
        if len(args) > 6:
            raise RuntimeError("Maximum number of arguments exceeded")
        cdef Arg arg
        for i, arg in enumerate(args):
            c_arg[i] = arg.to_c()
        if len(args) == 0:
            rc = libseccomp.seccomp_rule_add(self._ctx, action, syscall_num, 0)
        elif len(args) == 1:
            rc = libseccomp.seccomp_rule_add(self._ctx, action, syscall_num,
                                             len(args),
                                             c_arg[0])
        elif len(args) == 2:
            rc = libseccomp.seccomp_rule_add(self._ctx, action, syscall_num,
                                             len(args),
                                             c_arg[0],
                                             c_arg[1])
        elif len(args) == 3:
            rc = libseccomp.seccomp_rule_add(self._ctx, action, syscall_num,
                                             len(args),
                                             c_arg[0],
                                             c_arg[1],
                                             c_arg[2])
        elif len(args) == 4:
            rc = libseccomp.seccomp_rule_add(self._ctx, action, syscall_num,
                                             len(args),
                                             c_arg[0],
                                             c_arg[1],
                                             c_arg[2],
                                             c_arg[3])
        elif len(args) == 5:
            rc = libseccomp.seccomp_rule_add(self._ctx, action, syscall_num,
                                             len(args),
                                             c_arg[0],
                                             c_arg[1],
                                             c_arg[2],
                                             c_arg[3],
                                             c_arg[4])
        elif len(args) == 6:
            rc = libseccomp.seccomp_rule_add(self._ctx, action, syscall_num,
                                             len(args),
                                             c_arg[0],
                                             c_arg[1],
                                             c_arg[2],
                                             c_arg[3],
                                             c_arg[4],
                                             c_arg[5])
        else:
            raise RuntimeError("Maximum number of arguments exceeded")
        if rc != 0:
            raise RuntimeError(str.format("Library error (errno = {0})", rc))

    def add_rule_exactly(self, int action, syscall, *args):
        """ Add a new rule to filter.

        Arguments:
        action - the rule action: KILL_PROCESS, KILL, TRAP, ERRNO(), TRACE(),
                 LOG, or ALLOW
        syscall - the syscall name or number
        args - variable number of Arg objects

        Description:
        Add a new rule to the filter, matching on the given syscall and an
        optional list of argument comparisons.  If the rule is triggered
        the given action will be taken by the kernel.  In order for the
        rule to trigger, the syscall as well as each argument comparison
        must be true.

        This method attempts to add the filter rule exactly as specified
        which can cause problems on certain architectures, e.g. socket()
        on 32-bit x86.  For a architecture independent version of this
        method use add_rule().
        """
        cdef libseccomp.scmp_arg_cmp c_arg[6]
        if isinstance(syscall, str):
            syscall_str = syscall.encode()
            syscall_num = libseccomp.seccomp_syscall_resolve_name(syscall_str)
        elif isinstance(syscall, int):
            syscall_num = syscall
        else:
            raise TypeError("Syscall must either be an int or str type")
        """ NOTE: the code below exists solely to deal with the varadic
        nature of seccomp_rule_add_exact() function and the inability of
        Cython to handle this automatically """
        if len(args) > 6:
            raise RuntimeError("Maximum number of arguments exceeded")
        cdef Arg arg
        for i, arg in enumerate(args):
            c_arg[i] = arg.to_c()
        if len(args) == 0:
            rc = libseccomp.seccomp_rule_add_exact(self._ctx, action,
                                                   syscall_num, 0)
        elif len(args) == 1:
            rc = libseccomp.seccomp_rule_add_exact(self._ctx, action,
                                                   syscall_num, len(args),
                                                   c_arg[0])
        elif len(args) == 2:
            rc = libseccomp.seccomp_rule_add_exact(self._ctx, action,
                                                   syscall_num, len(args),
                                                   c_arg[0],
                                                   c_arg[1])
        elif len(args) == 3:
            rc = libseccomp.seccomp_rule_add_exact(self._ctx, action,
                                                   syscall_num, len(args),
                                                   c_arg[0],
                                                   c_arg[1],
                                                   c_arg[2])
        elif len(args) == 4:
            rc = libseccomp.seccomp_rule_add_exact(self._ctx, action,
                                                   syscall_num, len(args),
                                                   c_arg[0],
                                                   c_arg[1],
                                                   c_arg[2],
                                                   c_arg[3])
        elif len(args) == 5:
            rc = libseccomp.seccomp_rule_add_exact(self._ctx, action,
                                                   syscall_num, len(args),
                                                   c_arg[0],
                                                   c_arg[1],
                                                   c_arg[2],
                                                   c_arg[3],
                                                   c_arg[4])
        elif len(args) == 6:
            rc = libseccomp.seccomp_rule_add_exact(self._ctx, action,
                                                   syscall_num, len(args),
                                                   c_arg[0],
                                                   c_arg[1],
                                                   c_arg[2],
                                                   c_arg[3],
                                                   c_arg[4],
                                                   c_arg[5])
        else:
            raise RuntimeError("Maximum number of arguments exceeded")
        if rc != 0:
            raise RuntimeError(str.format("Library error (errno = {0})", rc))

    def export_pfc(self, file):
        """ Export the filter in PFC format.

        Arguments:
        file - the output file

        Description:
        Output the filter in Pseudo Filter Code (PFC) to the given file.
        The output is functionally equivalent to the BPF based filter
        which is loaded into the Linux Kernel.
        """
        rc = libseccomp.seccomp_export_pfc(self._ctx, file.fileno())
        if rc != 0:
            raise RuntimeError(str.format("Library error (errno = {0})", rc))

    def export_bpf(self, file):
        """ Export the filter in BPF format.

        Arguments:
        file - the output file

        Output the filter in Berkley Packet Filter (BPF) to the given
        file.  The output is identical to what is loaded into the
        Linux Kernel.
        """
        rc = libseccomp.seccomp_export_bpf(self._ctx, file.fileno())
        if rc != 0:
            raise RuntimeError(str.format("Library error (errno = {0})", rc))

# kate: syntax python;
# kate: indent-mode python; space-indent on; indent-width 4; mixedindent off;