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Improve hostwatch robustness and documentation.
If an exception occurs in hostwatch, sshuttle exits. Problems read/writing the ~/.sshuttle.hosts cache file on the remote machine would therefore cause sshuttle to exit. With this patch, we simply continue running without writing/reading the cache file in the remote home directory. This serves as an alternate fix for pull request #322 which proposed storing the cache file elsewhere. A list of included changes: - If we can't read or write the host cache file on the server, continue running. Hosts can be collected through the netstat, /etc/hosts, etc and the information can be reconstructed each run if a cache file isn't available to read. We write a log() message when this occurs. - Add additional types of exceptions to handle. - Continue even if we cannot read /etc/hosts on the server. - Update man page to mention the cache file on the remote host. - Indicate that messages are related to remote host instead of local host. - Add comments and descriptions to the code.
This commit is contained in:
Scott Kuhl
parent
a3cbf0885f
commit
560c6b4ce8
@ -89,6 +89,13 @@ Options
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few subnets over the VPN, you probably would prefer to
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keep using your local DNS server for everything else.
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:program:`sshuttle` tries to store a cache of the hostnames in
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~/.sshuttle.hosts on the remote host. Similarly, it tries to read
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the file when you later reconnect to the host with --auto-hosts
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enabled to quickly populate the host list. When troubleshooting
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this feature, try removing this file on the remote host when
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sshuttle is not running.
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.. option:: -N, --auto-nets
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In addition to the subnets provided on the command
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@ -178,7 +185,7 @@ Options
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A comma-separated list of hostnames to use to
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initialize the :option:`--auto-hosts` scan algorithm.
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:option:`--auto-hosts` does things like poll local SMB servers
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:option:`--auto-hosts` does things like poll netstat output
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for lists of local hostnames, but can speed things up
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if you use this option to give it a few names to start
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from.
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@ -29,9 +29,12 @@ except IOError:
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def _is_ip(s):
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return re.match(r'\d+\.\d+\.\d+\.\d+$', s)
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CACHE_WRITE_FAILED = False
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def write_host_cache():
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"""If possible, write our hosts file to disk so future connections
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can reuse the hosts that we already found."""
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tmpname = '%s.%d.tmp' % (CACHEFILE, os.getpid())
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global CACHE_WRITE_FAILED
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try:
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f = open(tmpname, 'wb')
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for name, ip in sorted(hostnames.items()):
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@ -39,7 +42,15 @@ def write_host_cache():
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f.close()
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os.chmod(tmpname, 384) # 600 in octal, 'rw-------'
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os.rename(tmpname, CACHEFILE)
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finally:
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CACHE_WRITE_FAILED = False
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except (OSError, IOError):
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# Write message if we haven't yet or if we get a failure after
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# a previous success.
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if not CACHE_WRITE_FAILED:
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log("Failed to write host cache to temporary file "
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"%s and rename it to %s" % (tmpname, CACHEFILE))
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CACHE_WRITE_FAILED = True
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try:
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os.unlink(tmpname)
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except BaseException:
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@ -47,25 +58,34 @@ def write_host_cache():
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def read_host_cache():
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"""If possible, read the cache file from disk to populate hosts that
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were found in a previous sshuttle run."""
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try:
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f = open(CACHEFILE)
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except IOError:
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except (OSError, IOError):
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_, e = sys.exc_info()[:2]
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if e.errno == errno.ENOENT:
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return
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else:
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raise
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log("Failed to read existing host cache file %s on remote host"
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% CACHEFILE)
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return
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for line in f:
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words = line.strip().split(',')
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if len(words) == 2:
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(name, ip) = words
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name = re.sub(r'[^-\w\.]', '-', name).strip()
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# Remove characters that shouldn't be in IP
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ip = re.sub(r'[^0-9.]', '', ip).strip()
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if name and ip:
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found_host(name, ip)
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def found_host(name, ip):
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"""The provided name maps to the given IP. Add the host to the
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hostnames list, send the host to the sshuttle client via
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stdout, and write the host to the cache file.
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"""
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hostname = re.sub(r'\..*', '', name)
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hostname = re.sub(r'[^-\w\.]', '_', hostname)
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if (ip.startswith('127.') or ip.startswith('255.') or
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@ -84,29 +104,37 @@ def found_host(name, ip):
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def _check_etc_hosts():
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debug2(' > hosts')
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for line in open('/etc/hosts'):
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line = re.sub(r'#.*', '', line)
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words = line.strip().split()
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if not words:
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continue
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ip = words[0]
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names = words[1:]
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if _is_ip(ip):
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debug3('< %s %r' % (ip, names))
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for n in names:
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check_host(n)
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found_host(n, ip)
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"""If possible, read /etc/hosts to find hosts."""
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filename = '/etc/hosts'
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debug2(' > Reading %s on remote host' % filename)
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try:
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for line in open(filename):
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line = re.sub(r'#.*', '', line) # remove comments
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words = line.strip().split()
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if not words:
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continue
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ip = words[0]
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if _is_ip(ip):
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names = words[1:]
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debug3('< %s %r' % (ip, names))
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for n in names:
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check_host(n)
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found_host(n, ip)
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except (OSError, IOError):
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debug1("Failed to read %s on remote host" % filename)
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def _check_revdns(ip):
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"""Use reverse DNS to try to get hostnames from an IP addresses."""
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debug2(' > rev: %s' % ip)
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try:
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r = socket.gethostbyaddr(ip)
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debug3('< %s' % r[0])
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check_host(r[0])
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found_host(r[0], ip)
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except (socket.herror, UnicodeError):
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except (OSError, socket.error, UnicodeError):
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# This case is expected to occur regularly.
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#debug3('< %s gethostbyaddr failed on remote host' % ip)
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pass
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@ -134,7 +162,14 @@ def _check_netstat():
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log('%r failed: %r' % (argv, e))
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return
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# The same IPs may appear multiple times. Consolidate them so the
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# debug message doesn't print the same IP repeatedly.
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ip_list = []
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for ip in re.findall(r'\d+\.\d+\.\d+\.\d+', content):
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if ip not in ip_list:
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ip_list.append(ip)
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for ip in sorted(ip_list):
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debug3('< %s' % ip)
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check_host(ip)
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@ -179,13 +214,19 @@ def hw_main(seed_hosts, auto_hosts):
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while 1:
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now = time.time()
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# For each item in the queue
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for t, last_polled in list(queue.items()):
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(op, args) = t
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if not _stdin_still_ok(0):
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break
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# Determine if we need to run.
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maxtime = POLL_TIME
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# netstat runs more often than other jobs
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if op == _check_netstat:
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maxtime = NETSTAT_POLL_TIME
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# Check if this jobs needs to run.
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if now - last_polled > maxtime:
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queue[t] = time.time()
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op(*args)
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@ -195,5 +236,5 @@ def hw_main(seed_hosts, auto_hosts):
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break
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# FIXME: use a smarter timeout based on oldest last_polled
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if not _stdin_still_ok(1):
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if not _stdin_still_ok(1): # sleeps for up to 1 second
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break
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