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dnsmasq-sandbox.patch
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dnsmasq-sandbox.patch
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diff --git a/Makefile b/Makefile
index 73ea23e..b6c7021 100644
--- a/Makefile
+++ b/Makefile
@@ -76,10 +76,11 @@ objs = cache.o rfc1035.o util.o option.o forward.o network.o \
helper.o tftp.o log.o conntrack.o dhcp6.o rfc3315.o \
dhcp-common.o outpacket.o radv.o slaac.o auth.o ipset.o \
domain.o dnssec.o blockdata.o tables.o loop.o inotify.o \
- poll.o rrfilter.o edns0.o arp.o
+ poll.o rrfilter.o edns0.o arp.o seccomp.o bpf-helper.o \
+ mount-namespace.o seccomp-testing.o
hdrs = dnsmasq.h config.h dhcp-protocol.h dhcp6-protocol.h \
- dns-protocol.h radv-protocol.h ip6addr.h
+ dns-protocol.h radv-protocol.h ip6addr.h bpf-helper.h
all : $(BUILDDIR)
@cd $(BUILDDIR) && $(MAKE) \
diff --git a/dnsmasq_sandbox_test.py b/dnsmasq_sandbox_test.py
new file mode 100755
index 0000000..24f7ffd
--- /dev/null
+++ b/dnsmasq_sandbox_test.py
@@ -0,0 +1,398 @@
+#!/usr/bin/python2
+""" dnsmasq is Copyright (c) 2000-2017 Simon Kelley
+
+ This program is free software; you can redistribute it and/or modify
+ it under the terms of the GNU General Public License as published by
+ the Free Software Foundation; version 2 dated June, 1991, or
+ (at your option) version 3 dated 29 June, 2007.
+
+ This program 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 General Public License for more details.
+
+ You should have received a copy of the GNU General Public License
+ along with this program. If not, see <http://www.gnu.org/licenses/>.
+
+Tests for dnsmasq_sandbox.
+
+Launch the dnsmasq instance and try to run "dig" with different types.
+
+In case of test failure you can do the following steps to fix the policy error:
+1) Using the syscall number, given by the test, lookup syscall name
+2) Edit the seccomp policy to temporary fully allow this syscall
+3) Run application with strace, e.g. strace -f src/dnsmasq [...]
+4) Using the log from strace, look at the syscall arguments to determine the
+appropriate seccomp policy for it
+5) Either fully allow the syscall or put additional restriction on its
+arguments
+
+The rule of thumb for dealing with arguments is to restrict them as much as
+you can.
+"""
+
+from __future__ import absolute_import
+from __future__ import division
+from __future__ import print_function
+
+import ctypes
+import errno
+import grp
+import os
+import pwd
+import random
+import re
+import shutil
+import signal
+import subprocess
+import time
+
+
+TESTING_DIR = 'dnsmasq_sandbox_testing/'
+LOG_FILE = 'dnsmasq.log'
+CONF_FILE = 'dnsmasq.conf'
+PID_FILE = 'dnsmasq.pid'
+PORT_NUMBER = 8951
+
+CLONE_NEWNET = 0x40000000
+DHCP_IPV4 = '10.0.0.1/24'
+DHCP_RANGEV4 = '10.0.0.2,10.0.0.100,10m'
+DHCP_IPV6 = '1:1:1:1:1:1:1:1/64'
+DHCP_RANGEV6 = '1:1:1:1:1:1:1:2,1:1:1:1:1:1:1:100,10m'
+
+TFTP_ROOT = 'dnsmasq_test_tftp_root'
+TFTP_TEST_FILE = 'test.txt'
+
+# Because of Ubuntu AppArmor policy we have to keep pid file at this location
+DHCLIENT_PID_FILE = '/var/run/dhclient_dnsmasq_testing.pid'
+
+BASE_CONFIG = ('domain-needed\n'
+ 'bogus-priv\n'
+ 'sandbox=force\n'
+ 'sandbox-test\n'
+ 'log-facility=%s\n'
+ 'pid-file=%s\n'
+ 'port=%d\n')
+
+DNSMASQ_PATH = 'src/dnsmasq'
+
+DIG_OPTIONS = ['tcp', 'aaonly', 'adflag', 'cdflag', 'recurse', 'dnssec',
+ 'nsid']
+DIG_TYPES = ['A', 'AAAA', 'ANY', 'CNAME', 'MX', 'NS', 'PTR', 'SOA', 'TXT',
+ 'A6', 'AFSDB', 'APL', 'ATMA', 'CAA', 'CERT', 'DNAME', 'DNSKEY',
+ 'DS', 'EID', 'GID', 'GPOS', 'HINFO', 'ISDN', 'KEY', 'KX', 'LOC',
+ 'MB', 'MD', 'MF', 'MG', 'MINFO', 'MR', 'MX', 'NAPTR', 'NIMLOC',
+ 'NSEC', 'NSEC3', 'NSEC3PARAM', 'NULL', 'NS', 'NSAP', 'NSAP-PTR',
+ 'NXT', 'OPT', 'PTR', 'PX', 'RP', 'RPSIG', 'RT', 'SIG', 'SINK',
+ 'SPF', 'SRV', 'SSHFP', 'TKEY', 'TLSA', 'TSIG', 'UID', 'UINFO',
+ 'UNSPEC', 'WKS', 'X25']
+
+WEBSITES = ['example.com', 'example.org']
+
+SYSCALL_RE = re.compile(r'Seccomp violation detected. Syscall number = (\d+)')
+
+
+def get_syscall_numbers(s):
+ return set(int(i) for i in SYSCALL_RE.findall(s))
+
+
+class DnsmasqTest(object):
+
+ def __init__(self):
+ cwd = os.getcwd()
+ self.testing_dir = os.path.join(cwd, TESTING_DIR)
+ self.config = ''
+ self.name = 'Test template'
+
+ def _log(self, msg, in_test=True):
+ print(('TEST:' if in_test else '') + msg)
+
+ def _report_error(self, numbers):
+ if not numbers:
+ self._log('dnsmasq error detected. '
+ 'Unable to determine bad syscall numbers')
+ return
+ self._log('Seccomp policy violation detected. Bad syscall numbers: %s'
+ % list(numbers))
+
+ def _get_pid(self):
+ try:
+ with open(self.pid_path, 'r') as f:
+ return int(f.read())
+ except (IOError, ValueError):
+ return None
+
+ def _start_dnsmasq(self):
+ self._log('starting dnsmasq instance')
+ with open(os.devnull, 'w') as devnull:
+ dnsmasq = subprocess.Popen([DNSMASQ_PATH, '-C', self.conf_path],
+ stdout=devnull,
+ stderr=subprocess.PIPE)
+ _, output = dnsmasq.communicate()
+ syscalls = get_syscall_numbers(output)
+ if dnsmasq.returncode != 0 and not syscalls:
+ self._log('dnsmasq died at setup')
+ self._log('return code = %d' % dnsmasq.returncode)
+ self._log('dnsmasq stderr = %s' % output.strip())
+ return 1
+ if syscalls:
+ self._report_error(syscalls)
+ return 1
+ self._log('dnsmasq setup complete')
+ return 0
+
+ def _kill_process(self):
+ pid = self._get_pid()
+ if pid:
+ try:
+ os.kill(pid, signal.SIGTERM)
+ time.sleep(1)
+ os.kill(pid, signal.SIGKILL)
+ except OSError:
+ pass
+
+ def _set_up(self):
+ try:
+ shutil.rmtree(TESTING_DIR)
+ except OSError as e:
+ if e.errno != errno.ENOENT:
+ raise
+ self.log_path = os.path.join(self.testing_dir, LOG_FILE)
+ self.conf_path = os.path.join(self.testing_dir, CONF_FILE)
+ self.pid_path = os.path.join(self.testing_dir, PID_FILE)
+ os.mkdir(TESTING_DIR)
+ # Ensuring, that log file exists and it is empty.
+ with open(self.log_path, 'w'):
+ pass
+ with open(self.conf_path, 'w') as f:
+ f.write(BASE_CONFIG % (self.log_path, self.pid_path, PORT_NUMBER))
+ f.write(self.config)
+
+ def _tear_down(self):
+ self._kill_process()
+ shutil.rmtree(TESTING_DIR)
+
+ def _run_test(self, name, f):
+ self._log('Running test %s' % name, False)
+ self._set_up()
+ result = f()
+ self._tear_down()
+ if not result:
+ self._log('Test %s: OK' % name, False)
+ else:
+ self._log('Test %s: FAILED' % name, False)
+
+ def run(self):
+ self._log('Running test group: %s' % self.name, False)
+ for name in dir(self):
+ if name.startswith('_test_') and callable(getattr(self, name)):
+ self._run_test(name[len('_test_'):], getattr(self, name))
+
+
+class DnsmasqDNSTest(DnsmasqTest):
+
+ def __init__(self):
+ super(DnsmasqDNSTest, self).__init__()
+ self.name = 'DNS seccomp'
+
+ def _set_up(self):
+ super(DnsmasqDNSTest, self)._set_up()
+
+ def _tear_down(self):
+ super(DnsmasqDNSTest, self)._tear_down()
+
+ def _test_dnsmasq_sandbox(self):
+ with open(os.devnull, 'w') as devnull:
+ if self._start_dnsmasq():
+ return 1
+ self._log('starting to run dig')
+ no_reply = 0
+ for dig_type in DIG_TYPES:
+ if no_reply:
+ break
+ self._log('running type = %s' % dig_type)
+ for option in DIG_OPTIONS:
+ url = random.choice(WEBSITES)
+ dig = subprocess.Popen(['dig', '-p', str(PORT_NUMBER), '@localhost',
+ '+' + option, '+time=1', '+tries=1', '+noall',
+ url, dig_type],
+ stdout=devnull,
+ stderr=devnull)
+ dig.wait()
+ if dig.returncode == 9:
+ no_reply = 1
+ break
+
+ self._kill_process()
+ with open(self.log_path, 'r') as f:
+ text = f.read()
+ syscalls = get_syscall_numbers(text)
+ if syscalls or no_reply:
+ self._report_error(syscalls)
+ return 1
+ return 0
+
+
+class DnsmasqDHCPTest(DnsmasqTest):
+
+ def __init__(self):
+ super(DnsmasqDHCPTest, self).__init__()
+ self.name = 'DHCP seccomp'
+ self.config = ('interface=veth0\n'
+ 'dhcp-range=%s\n'
+ 'dhcp-range=%s\n'
+ 'dhcp-alternate-port=1067,1068')
+ self.config = self.config % (DHCP_RANGEV4, DHCP_RANGEV6)
+
+ def _set_up(self):
+ super(DnsmasqDHCPTest, self)._set_up()
+ self.dhclient_pid = DHCLIENT_PID_FILE
+ # Setting up network namespace
+ libc = ctypes.CDLL(None, use_errno=True)
+ libc.unshare(CLONE_NEWNET)
+ with open(os.devnull, 'w') as devnull:
+ # Setting up virtual network interfaces
+ subprocess.call(['ip', 'link', 'add', 'veth0', 'type', 'veth', 'peer',
+ 'name', 'veth1'],
+ stdout=devnull,
+ stderr=devnull)
+ subprocess.call(['ip', 'link', 'set', 'veth0', 'up'],
+ stdout=devnull,
+ stderr=devnull)
+ subprocess.call(['ip', 'link', 'set', 'veth1', 'up'],
+ stdout=devnull,
+ stderr=devnull)
+ subprocess.call(['ip', 'addr', 'add', DHCP_IPV4, 'dev', 'veth0'],
+ stdout=devnull,
+ stderr=devnull)
+ subprocess.call(['ip', 'addr', 'add', DHCP_IPV6, 'dev', 'veth0'],
+ stdout=devnull,
+ stderr=devnull)
+
+ def _test_dhcp_v4(self):
+ if self._start_dnsmasq():
+ return 1
+ self._log('starting to run dhclient')
+ with open(os.devnull, 'w') as devnull:
+ self._log('acquiring lease')
+ subprocess.call(['timeout', '1m', 'dhclient', '-1',
+ '-pf', self.dhclient_pid, '-p', '1068', 'veth1'],
+ stdout=devnull,
+ stderr=devnull)
+ self._log('releasing lease')
+ subprocess.call(['timeout', '1m', 'dhclient', '-r',
+ '-pf', self.dhclient_pid, '-p', '1068', 'veth1'],
+ stdout=devnull,
+ stderr=devnull)
+ self._kill_process()
+ with open(self.log_path, 'r') as f:
+ text = f.read()
+ syscalls = get_syscall_numbers(text)
+ if syscalls:
+ self._report_error(syscalls)
+ return 1
+ return 0
+
+ def _test_dhcp_v6(self):
+ if self._start_dnsmasq():
+ return 1
+ self._log('starting to run dhclient')
+ with open(os.devnull, 'w') as devnull:
+ self._log('acquiring lease')
+ subprocess.call(['timeout', '1m', 'dhclient', '-6', '-1',
+ '-pf', self.dhclient_pid, 'veth1'],
+ stdout=devnull,
+ stderr=devnull)
+ self._log('releasing lease')
+ subprocess.call(['timeout', '1m', 'dhclient', '-6', '-r',
+ '-pf', self.dhclient_pid, 'veth1'],
+ stdout=devnull,
+ stderr=devnull)
+ self._kill_process()
+ with open(self.log_path, 'r') as f:
+ text = f.read()
+ syscalls = get_syscall_numbers(text)
+ if syscalls:
+ self._report_error(syscalls)
+ return 1
+ return 0
+
+ def _tear_down(self):
+ super(DnsmasqDHCPTest, self)._tear_down()
+ try:
+ with open(self.dhclient_pid, 'r') as f:
+ pid = int(f.read())
+ except (IOError, OSError, ValueError):
+ pid = None
+ if pid:
+ try:
+ os.kill(pid, signal.SIGKILL)
+ except OSError:
+ pass
+
+
+class DnsmasqTFTPTest(DnsmasqTest):
+
+ def __init__(self):
+ super(DnsmasqTFTPTest, self).__init__()
+ self.name = 'TFTP seccomp'
+ self.config = ('enable-tftp\n'
+ 'tftp-secure\n'
+ 'tftp-root=%s\n')
+ self.tftp_root = os.path.join(self.testing_dir, TFTP_ROOT)
+ self.config = self.config % self.tftp_root
+
+ def _set_up(self):
+ super(DnsmasqTFTPTest, self)._set_up()
+ nobody_uid = pwd.getpwnam('nobody').pw_uid
+ nogroup_gid = grp.getgrnam('nogroup').gr_gid
+ os.mkdir(self.tftp_root)
+ os.chown(self.tftp_root, nobody_uid, nogroup_gid)
+ self.tftp_root_file = os.path.join(self.tftp_root, TFTP_TEST_FILE)
+ self.tftp_file = os.path.join(self.testing_dir, TFTP_TEST_FILE)
+ with open(self.tftp_root_file, 'w') as f:
+ f.write('test\n')
+ os.chown(self.tftp_root_file, nobody_uid, nogroup_gid)
+
+ def _test_basic_tftp(self):
+ if self._start_dnsmasq():
+ return 1
+ self._log('starting to run tftp client')
+ with open(os.devnull, 'w') as devnull:
+ try:
+ subprocess.call(['busybox', 'tftp', '-g', '-l', self.tftp_file,
+ '-r', TFTP_TEST_FILE, 'localhost'],
+ stdout=devnull,
+ stderr=devnull)
+ except OSError as e:
+ if e.errno != errno.ENOENT:
+ raise
+ self._log('Failed to run tftp client. Perhaps it is not installed?')
+ return 1
+ self._kill_process()
+ with open(self.log_path, 'r') as f:
+ text = f.read()
+ syscalls = get_syscall_numbers(text)
+ if syscalls:
+ self._report_error(syscalls)
+ return 1
+ return 0
+
+ def _tear_down(self):
+ super(DnsmasqTFTPTest, self)._tear_down()
+
+
+def main():
+ test = DnsmasqDNSTest()
+ test.run()
+ test = DnsmasqTFTPTest()
+ test.run()
+ # Since DHCP test enters network namespace and mess up interfaces, we are
+ # doing it last
+ test = DnsmasqDHCPTest()
+ test.run()
+ print('Testing finished')
+
+if __name__ == '__main__':
+ main()
+
diff --git a/src/bpf-helper.c b/src/bpf-helper.c
new file mode 100644
index 0000000..1354988
--- /dev/null
+++ b/src/bpf-helper.c
@@ -0,0 +1,96 @@
+/*
+ * Seccomp BPF helper functions
+ *
+ * Copyright (c) 2012 The Chromium OS Authors <[email protected]>
+ * Author: Will Drewry <[email protected]>
+ *
+ * The code may be used by anyone for any purpose,
+ * and can serve as a starting point for developing
+ * applications using prctl(PR_ATTACH_SECCOMP_FILTER).
+ */
+
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+
+#include "bpf-helper.h"
+
+int bpf_resolve_jumps(struct bpf_labels *labels,
+ struct sock_filter *filter, size_t count)
+{
+ size_t i;
+
+ if (count < 1 || count > BPF_MAXINSNS)
+ return -1;
+ /*
+ * Walk it once, backwards, to build the label table and do fixups.
+ * Since backward jumps are disallowed by BPF, this is easy.
+ */
+ for (i = 0; i < count; ++i) {
+ size_t offset = count - i - 1;
+ struct sock_filter *instr = &filter[offset];
+ if (instr->code != (BPF_JMP+BPF_JA))
+ continue;
+ switch ((instr->jt<<8)|instr->jf) {
+ case (JUMP_JT<<8)|JUMP_JF:
+ if (labels->labels[instr->k].location == 0xffffffff) {
+ fprintf(stderr, "Unresolved label: '%s'\n",
+ labels->labels[instr->k].label);
+ return 1;
+ }
+ instr->k = labels->labels[instr->k].location -
+ (offset + 1);
+ instr->jt = 0;
+ instr->jf = 0;
+ continue;
+ case (LABEL_JT<<8)|LABEL_JF:
+ if (labels->labels[instr->k].location != 0xffffffff) {
+ fprintf(stderr, "Duplicate label use: '%s'\n",
+ labels->labels[instr->k].label);
+ return 1;
+ }
+ labels->labels[instr->k].location = offset;
+ instr->k = 0; /* fall through */
+ instr->jt = 0;
+ instr->jf = 0;
+ continue;
+ }
+ }
+ return 0;
+}
+
+/* Simple lookup table for labels. */
+__u32 seccomp_bpf_label(struct bpf_labels *labels, const char *label)
+{
+ struct __bpf_label *begin = labels->labels, *end;
+ int id;
+
+ if (labels->count == BPF_LABELS_MAX) {
+ fprintf(stderr, "Too many labels\n");
+ exit(1);
+ }
+ if (labels->count == 0) {
+ begin->label = label;
+ begin->location = 0xffffffff;
+ labels->count++;
+ return 0;
+ }
+ end = begin + labels->count;
+ for (id = 0; begin < end; ++begin, ++id) {
+ if (!strcmp(label, begin->label))
+ return id;
+ }
+ begin->label = label;
+ begin->location = 0xffffffff;
+ labels->count++;
+ return id;
+}
+
+void seccomp_bpf_print(struct sock_filter *filter, size_t count)
+{
+ struct sock_filter *end = filter + count;
+ for ( ; filter < end; ++filter)
+ printf("{ code=%u,jt=%u,jf=%u,k=%u },\n",
+ filter->code, filter->jt, filter->jf, filter->k);
+}
+
diff --git a/src/bpf-helper.h b/src/bpf-helper.h
new file mode 100644
index 0000000..e71a128
--- /dev/null
+++ b/src/bpf-helper.h
@@ -0,0 +1,268 @@
+/*
+ * Example wrapper around BPF macros.
+ *
+ * Copyright (c) 2012 The Chromium OS Authors <[email protected]>
+ * Author: Will Drewry <[email protected]>
+ *
+ * The code may be used by anyone for any purpose,
+ * and can serve as a starting point for developing
+ * applications using prctl(PR_SET_SECCOMP, 2, ...).
+ *
+ * No guarantees are provided with respect to the correctness
+ * or functionality of this code.
+ */
+#ifndef __BPF_HELPER_H__
+#define __BPF_HELPER_H__
+
+#include <asm/bitsperlong.h> /* for __BITS_PER_LONG */
+#include <endian.h>
+#include <linux/filter.h>
+#include <linux/seccomp.h> /* for seccomp_data */
+#include <linux/types.h>
+#include <linux/unistd.h>
+#include <stddef.h>
+
+#define BPF_LABELS_MAX 256
+struct bpf_labels {
+ int count;
+ struct __bpf_label {
+ const char *label;
+ __u32 location;
+ } labels[BPF_LABELS_MAX];
+};
+
+int bpf_resolve_jumps(struct bpf_labels *labels,
+ struct sock_filter *filter, size_t count);
+__u32 seccomp_bpf_label(struct bpf_labels *labels, const char *label);
+void seccomp_bpf_print(struct sock_filter *filter, size_t count);
+
+#define JUMP_JT 0xff
+#define JUMP_JF 0xff
+#define LABEL_JT 0xfe
+#define LABEL_JF 0xfe
+
+#define ALLOW \
+ BPF_STMT(BPF_RET+BPF_K, SECCOMP_RET_ALLOW)
+#define DENY \
+ BPF_STMT(BPF_RET+BPF_K, SECCOMP_RET_KILL)
+#define TRAP \
+ BPF_STMT(BPF_RET+BPF_K, SECCOMP_RET_TRAP)
+#define JUMP(labels, label) \
+ BPF_JUMP(BPF_JMP+BPF_JA, FIND_LABEL((labels), (label)), \
+ JUMP_JT, JUMP_JF)
+#define LABEL(labels, label) \
+ BPF_JUMP(BPF_JMP+BPF_JA, FIND_LABEL((labels), (label)), \
+ LABEL_JT, LABEL_JF)
+#define SYSCALL(nr, jt) \
+ BPF_JUMP(BPF_JMP+BPF_JEQ+BPF_K, (nr), 0, 1), \
+ jt
+
+/* Lame, but just an example */
+#define FIND_LABEL(labels, label) seccomp_bpf_label((labels), #label)
+
+#define EXPAND(...) __VA_ARGS__
+
+/* Ensure that we load the logically correct offset. */
+#if __BYTE_ORDER == __LITTLE_ENDIAN
+#define LO_ARG(idx) offsetof(struct seccomp_data, args[(idx)])
+#elif __BYTE_ORDER == __BIG_ENDIAN
+#define LO_ARG(idx) offsetof(struct seccomp_data, args[(idx)]) + sizeof(__u32)
+#else
+#error "Unknown endianness"
+#endif
+
+/* Map all width-sensitive operations */
+#if __BITS_PER_LONG == 32
+
+#define JEQ(x, jt) JEQ32(x, EXPAND(jt))
+#define JNE(x, jt) JNE32(x, EXPAND(jt))
+#define JGT(x, jt) JGT32(x, EXPAND(jt))
+#define JLT(x, jt) JLT32(x, EXPAND(jt))
+#define JGE(x, jt) JGE32(x, EXPAND(jt))
+#define JLE(x, jt) JLE32(x, EXPAND(jt))
+#define JA(x, jt) JA32(x, EXPAND(jt))
+#define ARG(i) ARG_32(i)
+
+#elif __BITS_PER_LONG == 64
+
+/* Ensure that we load the logically correct offset. */
+#if __BYTE_ORDER == __LITTLE_ENDIAN
+#define ENDIAN(_lo, _hi) _lo, _hi
+#define HI_ARG(idx) offsetof(struct seccomp_data, args[(idx)]) + sizeof(__u32)
+#elif __BYTE_ORDER == __BIG_ENDIAN
+#define ENDIAN(_lo, _hi) _hi, _lo
+#define HI_ARG(idx) offsetof(struct seccomp_data, args[(idx)])
+#endif
+
+union arg64 {
+ struct {
+ __u32 ENDIAN(lo32, hi32);
+ };
+ __u64 u64;
+};
+
+#define JEQ(x, jt) \
+ JEQ64(((union arg64){.u64 = (x)}).lo32, \
+ ((union arg64){.u64 = (x)}).hi32, \
+ EXPAND(jt))
+#define JGT(x, jt) \
+ JGT64(((union arg64){.u64 = (x)}).lo32, \
+ ((union arg64){.u64 = (x)}).hi32, \
+ EXPAND(jt))
+#define JGE(x, jt) \
+ JGE64(((union arg64){.u64 = (x)}).lo32, \
+ ((union arg64){.u64 = (x)}).hi32, \
+ EXPAND(jt))
+#define JNE(x, jt) \
+ JNE64(((union arg64){.u64 = (x)}).lo32, \
+ ((union arg64){.u64 = (x)}).hi32, \
+ EXPAND(jt))
+#define JLT(x, jt) \
+ JLT64(((union arg64){.u64 = (x)}).lo32, \
+ ((union arg64){.u64 = (x)}).hi32, \
+ EXPAND(jt))
+#define JLE(x, jt) \
+ JLE64(((union arg64){.u64 = (x)}).lo32, \
+ ((union arg64){.u64 = (x)}).hi32, \
+ EXPAND(jt))
+
+#define JA(x, jt) \
+ JA64(((union arg64){.u64 = (x)}).lo32, \
+ ((union arg64){.u64 = (x)}).hi32, \
+ EXPAND(jt))
+#define ARG(i) ARG_64(i)
+
+#else
+#error __BITS_PER_LONG value unusable.
+#endif
+
+/* Loads the arg into A */
+#define ARG_32(idx) \
+ BPF_STMT(BPF_LD+BPF_W+BPF_ABS, LO_ARG(idx))
+
+/* Loads lo into M[0] and hi into M[1] and A */
+#define ARG_64(idx) \
+ BPF_STMT(BPF_LD+BPF_W+BPF_ABS, LO_ARG(idx)), \
+ BPF_STMT(BPF_ST, 0), /* lo -> M[0] */ \
+ BPF_STMT(BPF_LD+BPF_W+BPF_ABS, HI_ARG(idx)), \
+ BPF_STMT(BPF_ST, 1) /* hi -> M[1] */
+
+#define JEQ32(value, jt) \
+ BPF_JUMP(BPF_JMP+BPF_JEQ+BPF_K, (value), 0, 1), \
+ jt
+
+#define JNE32(value, jt) \
+ BPF_JUMP(BPF_JMP+BPF_JEQ+BPF_K, (value), 1, 0), \
+ jt
+
+#define JA32(value, jt) \
+ BPF_JUMP(BPF_JMP+BPF_JSET+BPF_K, (value), 0, 1), \
+ jt
+
+#define JGE32(value, jt) \
+ BPF_JUMP(BPF_JMP+BPF_JGE+BPF_K, (value), 0, 1), \
+ jt
+
+#define JGT32(value, jt) \
+ BPF_JUMP(BPF_JMP+BPF_JGT+BPF_K, (value), 0, 1), \
+ jt
+
+#define JLE32(value, jt) \
+ BPF_JUMP(BPF_JMP+BPF_JGT+BPF_K, (value), 1, 0), \
+ jt
+
+#define JLT32(value, jt) \
+ BPF_JUMP(BPF_JMP+BPF_JGE+BPF_K, (value), 1, 0), \
+ jt
+
+/*
+ * All the JXX64 checks assume lo is saved in M[0] and hi is saved in both
+ * A and M[1]. This invariant is kept by restoring A if necessary.
+ */
+#define JEQ64(lo, hi, jt) \
+ /* if (hi != arg.hi) goto NOMATCH; */ \
+ BPF_JUMP(BPF_JMP+BPF_JEQ+BPF_K, (hi), 0, 5), \
+ BPF_STMT(BPF_LD+BPF_MEM, 0), /* swap in lo */ \
+ /* if (lo != arg.lo) goto NOMATCH; */ \
+ BPF_JUMP(BPF_JMP+BPF_JEQ+BPF_K, (lo), 0, 2), \
+ BPF_STMT(BPF_LD+BPF_MEM, 1), \
+ jt, \
+ BPF_STMT(BPF_LD+BPF_MEM, 1)
+
+#define JNE64(lo, hi, jt) \
+ /* if (hi != arg.hi) goto MATCH; */ \
+ BPF_JUMP(BPF_JMP+BPF_JEQ+BPF_K, (hi), 0, 3), \
+ BPF_STMT(BPF_LD+BPF_MEM, 0), \
+ /* if (lo != arg.lo) goto MATCH; */ \
+ BPF_JUMP(BPF_JMP+BPF_JEQ+BPF_K, (lo), 2, 0), \
+ BPF_STMT(BPF_LD+BPF_MEM, 1), \
+ jt, \
+ BPF_STMT(BPF_LD+BPF_MEM, 1)
+
+#define JA64(lo, hi, jt) \
+ /* if (hi & arg.hi) goto MATCH; */ \
+ BPF_JUMP(BPF_JMP+BPF_JSET+BPF_K, (hi), 3, 0), \
+ BPF_STMT(BPF_LD+BPF_MEM, 0), \
+ /* if (lo & arg.lo) goto MATCH; */ \
+ BPF_JUMP(BPF_JMP+BPF_JSET+BPF_K, (lo), 0, 2), \
+ BPF_STMT(BPF_LD+BPF_MEM, 1), \
+ jt, \
+ BPF_STMT(BPF_LD+BPF_MEM, 1)
+
+#define JGE64(lo, hi, jt) \
+ /* if (hi > arg.hi) goto MATCH; */ \
+ BPF_JUMP(BPF_JMP+BPF_JGT+BPF_K, (hi), 4, 0), \
+ /* if (hi != arg.hi) goto NOMATCH; */ \
+ BPF_JUMP(BPF_JMP+BPF_JEQ+BPF_K, (hi), 0, 5), \
+ BPF_STMT(BPF_LD+BPF_MEM, 0), \
+ /* if (lo >= arg.lo) goto MATCH; */ \
+ BPF_JUMP(BPF_JMP+BPF_JGE+BPF_K, (lo), 0, 2), \
+ BPF_STMT(BPF_LD+BPF_MEM, 1), \
+ jt, \
+ BPF_STMT(BPF_LD+BPF_MEM, 1)
+
+#define JGT64(lo, hi, jt) \
+ /* if (hi > arg.hi) goto MATCH; */ \
+ BPF_JUMP(BPF_JMP+BPF_JGT+BPF_K, (hi), 4, 0), \
+ /* if (hi != arg.hi) goto NOMATCH; */ \
+ BPF_JUMP(BPF_JMP+BPF_JEQ+BPF_K, (hi), 0, 5), \
+ BPF_STMT(BPF_LD+BPF_MEM, 0), \
+ /* if (lo > arg.lo) goto MATCH; */ \
+ BPF_JUMP(BPF_JMP+BPF_JGT+BPF_K, (lo), 0, 2), \
+ BPF_STMT(BPF_LD+BPF_MEM, 1), \
+ jt, \
+ BPF_STMT(BPF_LD+BPF_MEM, 1)
+
+#define JLE64(lo, hi, jt) \
+ /* if (hi < arg.hi) goto MATCH; */ \
+ BPF_JUMP(BPF_JMP+BPF_JGE+BPF_K, (hi), 0, 4), \
+ /* if (hi != arg.hi) goto NOMATCH; */ \
+ BPF_JUMP(BPF_JMP+BPF_JEQ+BPF_K, (hi), 0, 5), \
+ BPF_STMT(BPF_LD+BPF_MEM, 0), \
+ /* if (lo <= arg.lo) goto MATCH; */ \
+ BPF_JUMP(BPF_JMP+BPF_JGT+BPF_K, (lo), 2, 0), \
+ BPF_STMT(BPF_LD+BPF_MEM, 1), \
+ jt, \
+ BPF_STMT(BPF_LD+BPF_MEM, 1)
+
+#define JLT64(lo, hi, jt) \
+ /* if (hi < arg.hi) goto MATCH; */ \
+ BPF_JUMP(BPF_JMP+BPF_JGE+BPF_K, (hi), 0, 4), \
+ /* if (hi != arg.hi) goto NOMATCH; */ \
+ BPF_JUMP(BPF_JMP+BPF_JEQ+BPF_K, (hi), 0, 5), \
+ BPF_STMT(BPF_LD+BPF_MEM, 0), \
+ /* if (lo < arg.lo) goto MATCH; */ \
+ BPF_JUMP(BPF_JMP+BPF_JGE+BPF_K, (lo), 2, 0), \
+ BPF_STMT(BPF_LD+BPF_MEM, 1), \
+ jt, \
+ BPF_STMT(BPF_LD+BPF_MEM, 1)
+
+#define LOAD_SYSCALL_NR \
+ BPF_STMT(BPF_LD+BPF_W+BPF_ABS, \
+ offsetof(struct seccomp_data, nr))
+#define LOAD_ARCH \
+ BPF_STMT(BPF_LD+BPF_W+BPF_ABS, \
+ offsetof(struct seccomp_data, arch))
+
+#endif /* __BPF_HELPER_H__ */
+
diff --git a/src/config.h b/src/config.h
index 4c03e2c..3f5ef52 100644
--- a/src/config.h
+++ b/src/config.h
@@ -180,6 +180,7 @@ RESOLVFILE
/* #define HAVE_LIBIDN2 */
/* #define HAVE_CONNTRACK */
/* #define HAVE_DNSSEC */
+/* #define HAVE_SECCOMP */
/* Default locations for important system files. */
@@ -232,6 +233,10 @@ HAVE_GETOPT_LONG
HAVE_SOCKADDR_SA_LEN
defined if struct sockaddr has sa_len field (*BSD)
+
+HAVE_SECCOMP
+ defined if seccomp-bpf and mount namespaces Linux-only features are
+ available, to enable the sandbox code.
*/
/* Must precede __linux__ since uClinux defines __linux__ too. */
@@ -265,6 +270,10 @@ HAVE_SOCKADDR_SA_LEN
#elif defined(__linux__)
#define HAVE_LINUX_NETWORK
#define HAVE_GETOPT_LONG
+#if defined(__x86_64__) || defined(__i386__) || defined(__aarch64__) || \
+ defined(__arm__) || defined(__powerpc__)
+#define HAVE_SECCOMP
+#endif
#undef HAVE_SOCKADDR_SA_LEN
#elif defined(__FreeBSD__) || \
@@ -365,6 +374,10 @@ HAVE_SOCKADDR_SA_LEN
#undef HAVE_LOOP
#endif
+#ifdef NO_SECCOMP
+#undef HAVE_SECCOMP
+#endif
+
#if defined (HAVE_LINUX_NETWORK) && !defined(NO_INOTIFY)
#define HAVE_INOTIFY
#endif
@@ -443,6 +456,10 @@ static char *compile_opts =
"no-"
#endif
"DNSSEC "
+#ifndef HAVE_SECCOMP
+"no-"
+#endif
+"SECCOMP "
#ifdef NO_ID
"no-ID "
#endif
diff --git a/src/dnsmasq.c b/src/dnsmasq.c
index 771bec1..79562b3 100644
--- a/src/dnsmasq.c
+++ b/src/dnsmasq.c
@@ -67,7 +67,6 @@ int main (int argc, char **argv)
bindtextdomain("dnsmasq", LOCALEDIR);
textdomain("dnsmasq");
#endif
-
sigact.sa_handler = sig_handler;
sigact.sa_flags = 0;
sigemptyset(&sigact.sa_mask);
@@ -87,7 +86,27 @@ int main (int argc, char **argv)
rand_init(); /* Must precede read_opts() */
read_opts(argc, argv, compile_opts);
-
+
+ /* Enabling sandbox */
+#ifndef HAVE_SECCOMP
+ if (!option_bool(OPT_NO_SANDBOX) && option_bool(OPT_SANDBOX_FORCE))
+ {
+ die(_("Seccomp not available: see HAVE_SECCOMP in src/config.h"), NULL, EC_BADCONF);
+ }
+#else
+ if (!option_bool(OPT_NO_SANDBOX))
+ {
+ if (setup_mount_namespace(daemon) && option_bool(OPT_SANDBOX_FORCE))
+ {
+ die(_("mount namespace initialization failed"), NULL, EC_MISC);
+ }
+ if (setup_seccomp(daemon) && option_bool(OPT_SANDBOX_FORCE))
+ {
+ die(_("seccomp initialization failed"), NULL, EC_MISC);
+ }
+ }
+#endif
+
if (daemon->edns_pktsz < PACKETSZ)
daemon->edns_pktsz = PACKETSZ;
diff --git a/src/dnsmasq.h b/src/dnsmasq.h
index 24dda08..ae85dc9 100644
--- a/src/dnsmasq.h
+++ b/src/dnsmasq.h
@@ -239,7 +239,10 @@ struct event_desc {
#define OPT_MAC_B64 54
#define OPT_MAC_HEX 55
#define OPT_TFTP_APREF_MAC 56
-#define OPT_LAST 57
+#define OPT_NO_SANDBOX 57
+#define OPT_SANDBOX_FORCE 58
+#define OPT_SANDBOX_TEST 59
+#define OPT_LAST 60
/* extra flags for my_syslog, we use a couple of facilities since they are known
not to occupy the same bits as priorities, no matter how syslog.h is set up. */
@@ -1558,3 +1561,19 @@ int check_source(struct dns_header *header, size_t plen, unsigned char *pseudohe
/* arp.c */
int find_mac(union mysockaddr *addr, unsigned char *mac, int lazy, time_t now);
int do_arp_script_run(void);
+
+/* seccomp.c */
+#ifdef HAVE_SECCOMP
+int setup_seccomp(struct daemon *daemon);
+#endif
+
+/* seccomp-testing.c */
+#ifdef HAVE_SECCOMP
+int setup_seccomp_testing();
+#endif
+
+/* mount-namespace.c */
+#ifdef HAVE_SECCOMP
+int setup_mount_namespace(struct daemon *daemon);
+#endif
+
diff --git a/src/mount-namespace.c b/src/mount-namespace.c
new file mode 100644
index 0000000..c3a6f8e
--- /dev/null
+++ b/src/mount-namespace.c
@@ -0,0 +1,387 @@
+/* dnsmasq is Copyright (c) 2000-2017 Simon Kelley
+
+ This program is free software; you can redistribute it and/or modify
+ it under the terms of the GNU General Public License as published by
+ the Free Software Foundation; version 2 dated June, 1991, or
+ (at your option) version 3 dated 29 June, 2007.
+
+ This program 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 General Public License for more details.
+
+ You should have received a copy of the GNU General Public License
+ along with this program. If not, see <http://www.gnu.org/licenses/>.
+*/
+
+/* Using linux mount namespace implementation to limit dnsmasq access to files.
+
+ Basically, we create a copy of the file tree in /tmp, including only files
+ and directories, necessary for the dnsmasq, mount them to their
+ versions in the original file tree and then do pivot_root into this folder
+ to prevent possible escapes. While seccomp restrict syscalls, a mount
+ namespace complements this by restricting which files can be read and
+ modified on the filesystem, so we end up with a robust sandbox.
+ Also we create a copy of our cwd in our fake tree and chdir into it later,
+ so all relative links still work.
+
+ We use mount namespaces, so all mount operations we do to establish our
+ sandbox, doesn't affect anything outside dnsmasq process.
+
+ If you want to add a file or directory there are two possibilities:
+ 1) The file or directory only need to exist, doesn't hold any data on the
+ beginning and you don't need to save the data between dnsmasq launches.
+ Then you use: create_sandbox_dir / create_sandbox_file.
+ Examples:
+ create_sandbox_file("/tmp/dnsmasq_tmp_cache")
+ create_sandbox_dir(cwd) // to chdir into it later, we don't really
+ need its content.
+ 2) You need the contents of the file/dir to be reachable by application.
+ Then you use: mount_dir / mount_file.
+ Examples:
+ mount_dir("/var/dnsmasq/hosts_file_directory")
+ mount_file("/etc/resolv.conf") */
+
+#include "dnsmasq.h"
+
+#ifdef HAVE_SECCOMP
+
+#include <sched.h>
+#include <libgen.h>
+#include <sys/mount.h>
+#include <sys/syscall.h>
+
+#define MOUNT_ROOT "/tmp/dnsmasq.sandbox"
+#define MOUNT_FILE 0
+#define MOUNT_DIR 1
+
+static char *cwd;
+
+static char* join_paths(char *first, char *second)
+{
+ /* +2 for null byte and slash, that may be added */
+ char *result = safe_malloc(strlen(first) + strlen(second) + 2);