zeroinstall/injector/gpg.py

   1 """
   2 Python interface to GnuPG.
   3
   4 This module is used to invoke GnuPG to check the digital signatures on interfaces.
   5
   6 @see: L{iface_cache.PendingFeed}
   7 """
   8
   9 # Copyright (C) 2009, Thomas Leonard
  10 # See the README file for details, or visit http://0install.net.
  11
  12 import subprocess
  13 import base64, re
  14 import os
  15 import tempfile
  16 from logging import info
  17
  18 from zeroinstall.support import find_in_path, basedir
  19 from zeroinstall.injector.trust import trust_db
  20 from zeroinstall.injector.model import SafeException
  21
  22 _gnupg_options = ['gpg', '--no-secmem-warning']
  23 if hasattr(os, 'geteuid') and os.geteuid() == 0 and 'GNUPGHOME' not in os.environ:
  24         _gnupg_options += ['--homedir', os.path.join(basedir.home, '.gnupg')]
  25         info("Running as root, so setting GnuPG home to %s", _gnupg_options[-1])
  26
  27 class Signature(object):
  28         """Abstract base class for signature check results."""
  29         status = None
  30
  31         def __init__(self, status):
  32                 self.status = status
  33
  34         def is_trusted(self, domain = None):
  35                 """Whether this signature is trusted by the user."""
  36                 return False
  37
  38         def need_key(self):
  39                 """Returns the ID of the key that must be downloaded to check this signature."""
  40                 return None
  41
  42 class ValidSig(Signature):
  43         """A valid signature check result."""
  44         FINGERPRINT = 0
  45         TIMESTAMP = 2
  46
  47         def __str__(self):
  48                 return "Valid signature from " + self.status[self.FINGERPRINT]
  49
  50         def is_trusted(self, domain = None):
  51                 """Asks the L{trust.trust_db}."""
  52                 return trust_db.is_trusted(self.status[self.FINGERPRINT], domain)
  53
  54         def get_timestamp(self):
  55                 """Get the time this signature was made."""
  56                 return int(self.status[self.TIMESTAMP])
  57
  58         fingerprint = property(lambda self: self.status[self.FINGERPRINT])
  59
  60         def get_details(self):
  61                 """Call 'gpg --list-keys' and return the results split into lines and columns.
  62                 @rtype: [[str]]"""
  63                 child = subprocess.Popen(_gnupg_options + ['--with-colons', '--list-keys', self.fingerprint], stdout = subprocess.PIPE)
  64                 cout, unused = child.communicate()
  65                 if child.returncode:
  66                         info("GPG exited with code %d" % child.returncode)
  67                 details = []
  68                 for line in cout.split('\n'):
  69                         details.append(line.split(':'))
  70                 return details
  71
  72 class BadSig(Signature):
  73         """A bad signature (doesn't match the message)."""
  74         KEYID = 0
  75
  76         def __str__(self):
  77                 return "BAD signature by " + self.status[self.KEYID] + \
  78                         " (the message has been tampered with)"
  79
  80 class ErrSig(Signature):
  81         """Error while checking a signature."""
  82         KEYID = 0
  83         ALG = 1
  84         RC = -1
  85
  86         def __str__(self):
  87                 msg = "ERROR signature by %s: " % self.status[self.KEYID]
  88                 rc = int(self.status[self.RC])
  89                 if rc == 4:
  90                         msg += "Unknown or unsupported algorithm '%s'" % self.status[self.ALG]
  91                 elif rc == 9:
  92                         msg += "Unknown key. Try 'gpg --recv-key %s'" % self.status[self.KEYID]
  93                 else:
  94                         msg += "Unknown reason code %d" % rc
  95                 return msg
  96
  97         def need_key(self):
  98                 rc = int(self.status[self.RC])
  99                 if rc == 9:
 100                         return self.status[self.KEYID]
 101                 return None
 102
 103 class Key:
 104         """A GPG key.
 105         @since: 0.27
 106         @param fingerprint: the fingerprint of the key
 107         @type fingerprint: str
 108         @ivar name: a short name for the key, extracted from the full name
 109         @type name: str
 110         """
 111         def __init__(self, fingerprint):
 112                 self.fingerprint = fingerprint
 113                 self.name = '(unknown)'
 114
 115         def get_short_name(self):
 116                 return self.name.split(' (', 1)[0].split(' <', 1)[0]
 117
 118 def load_keys(fingerprints):
 119         """Load a set of keys at once.
 120         This is much more efficient than making individual calls to L{load_key}.
 121         @return: a list of loaded keys, indexed by fingerprint
 122         @rtype: {str: L{Key}}
 123         @since: 0.27"""
 124
 125         keys = {}
 126
 127         # Otherwise GnuPG returns everything...
 128         if not fingerprints: return keys
 129
 130         for fp in fingerprints:
 131                 keys[fp] = Key(fp)
 132
 133         current_fpr = None
 134         current_uid = None
 135
 136         cin, cout = os.popen2(_gnupg_options + ['--fixed-list-mode', '--with-colons', '--list-keys',
 137                                 '--with-fingerprint', '--with-fingerprint'] + fingerprints)
 138         cin.close()
 139         try:
 140                 for line in cout:
 141                         if line.startswith('pub:'):
 142                                 current_fpr = None
 143                                 current_uid = None
 144                         if line.startswith('fpr:'):
 145                                 current_fpr = line.split(':')[9]
 146                                 if current_fpr in keys and current_uid:
 147                                         # This is probably a subordinate key, where the fingerprint
 148                                         # comes after the uid, not before. Note: we assume the subkey is
 149                                         # cross-certified, as recent always ones are.
 150                                         keys[current_fpr].name = current_uid
 151                         if line.startswith('uid:'):
 152                                 assert current_fpr is not None
 153                                 # Only take primary UID
 154                                 if current_uid: continue
 155                                 parts = line.split(':')
 156                                 current_uid = parts[9]
 157                                 if current_fpr in keys:
 158                                         keys[current_fpr].name = current_uid
 159         finally:
 160                 cout.close()
 161
 162         return keys
 163
 164 def load_key(fingerprint):
 165         """Query gpg for information about this key.
 166         @return: a new key
 167         @rtype: L{Key}
 168         @since: 0.27"""
 169         return load_keys([fingerprint])[fingerprint]
 170
 171 def import_key(stream):
 172         """Run C{gpg --import} with this stream as stdin."""
 173         errors = tempfile.TemporaryFile()
 174
 175         child = subprocess.Popen(_gnupg_options + ['--quiet', '--import'],
 176                                 stdin = stream, stderr = errors)
 177
 178         status = child.wait()
 179
 180         errors.seek(0)
 181         error_messages = errors.read().strip()
 182         errors.close()
 183
 184         if error_messages:
 185                 raise SafeException("Errors from 'gpg --import':\n%s" % error_messages)
 186
 187 def _check_plain_stream(stream):
 188         data = tempfile.TemporaryFile() # Python2.2 does not support 'prefix'
 189         errors = tempfile.TemporaryFile()
 190
 191         status_r, status_w = os.pipe()
 192
 193         # Note: Should ideally close status_r in the child, but we want to support Windows too
 194         child = subprocess.Popen(_gnupg_options + ['--decrypt',
 195                                            # Not all versions support this:
 196                                            #'--max-output', str(1024 * 1024),
 197                                            '--batch',
 198                                            '--status-fd', str(status_w)],
 199                                 stdin = stream,
 200                                 stdout = data,
 201                                 stderr = errors)
 202
 203         os.close(status_w)
 204
 205         try:
 206                 sigs = _get_sigs_from_gpg_status_stream(os.fdopen(status_r), child, errors)
 207         finally:
 208                 data.seek(0)
 209         return (data, sigs)
 210
 211 def _check_xml_stream(stream):
 212         xml_comment_start = '<!-- Base64 Signature'
 213
 214         data_to_check = stream.read()
 215
 216         last_comment = data_to_check.rfind('\n' + xml_comment_start)
 217         if last_comment < 0:
 218                 raise SafeException("No signature block in XML. Maybe this file isn't signed?")
 219         last_comment += 1       # Include new-line in data
 220
 221         data = tempfile.TemporaryFile()
 222         data.write(data_to_check[:last_comment])
 223         data.flush()
 224         os.lseek(data.fileno(), 0, 0)
 225
 226         errors = tempfile.TemporaryFile()
 227
 228         sig_lines = data_to_check[last_comment:].split('\n')
 229         if sig_lines[0].strip() != xml_comment_start:
 230                 raise SafeException('Bad signature block: extra data on comment line')
 231         while sig_lines and not sig_lines[-1].strip():
 232                 del sig_lines[-1]
 233         if sig_lines[-1].strip() != '-->':
 234                 raise SafeException('Bad signature block: last line is not end-of-comment')
 235         sig_data = '\n'.join(sig_lines[1:-1])
 236
 237         if re.match('^[ A-Za-z0-9+/=\n]+$', sig_data) is None:
 238                 raise SafeException("Invalid characters found in base 64 encoded signature")
 239         try:
 240                 sig_data = base64.decodestring(sig_data) # (b64decode is Python 2.4)
 241         except Exception, ex:
 242                 raise SafeException("Invalid base 64 encoded signature: " + str(ex))
 243
 244         sig_fd, sig_name = tempfile.mkstemp(prefix = 'injector-sig-')
 245         try:
 246                 sig_file = os.fdopen(sig_fd, 'w')
 247                 sig_file.write(sig_data)
 248                 sig_file.close()
 249
 250                 # Note: Should ideally close status_r in the child, but we want to support Windows too
 251                 child = subprocess.Popen(_gnupg_options + [
 252                                                    # Not all versions support this:
 253                                                    #'--max-output', str(1024 * 1024),
 254                                                    '--batch',
 255                                                    # Windows GPG can only cope with "1" here
 256                                                    '--status-fd', '1',
 257                                                    '--verify', sig_name, '-'],
 258                                                    stdin = data,
 259                                                    stdout = subprocess.PIPE,
 260                                                    stderr = errors)
 261
 262                 try:
 263                         sigs = _get_sigs_from_gpg_status_stream(child.stdout, child, errors)
 264                 finally:
 265                         os.lseek(stream.fileno(), 0, 0)
 266                         stream.seek(0)
 267         finally:
 268                 os.unlink(sig_name)
 269         return (stream, sigs)
 270
 271 def check_stream(stream):
 272         """Pass stream through gpg --decrypt to get the data, the error text,
 273         and a list of signatures (good or bad). If stream starts with "<?xml "
 274         then get the signature from a comment at the end instead (and the returned
 275         data is the original stream). stream must be seekable.
 276         @note: Stream returned may or may not be the one passed in. Be careful!
 277         @return: (data_stream, [Signatures])"""
 278         if not find_in_path('gpg'):
 279                 raise SafeException("GnuPG is not installed ('gpg' not in $PATH). See http://gnupg.org")
 280
 281         #stream.seek(0)
 282         #all = stream.read()
 283         stream.seek(0)
 284
 285         start = stream.read(6)
 286         stream.seek(0)
 287         if start == "<?xml ":
 288                 return _check_xml_stream(stream)
 289         elif start == '-----B':
 290                 import warnings
 291                 warnings.warn("Plain GPG-signed feeds are deprecated!", DeprecationWarning, stacklevel = 2)
 292                 os.lseek(stream.fileno(), 0, 0)
 293                 return _check_plain_stream(stream)
 294         else:
 295                 raise SafeException("This is not a Zero Install feed! It should be an XML document, but it starts:\n%s" % repr(stream.read(120)))
 296
 297 def _get_sigs_from_gpg_status_stream(status_r, child, errors):
 298         """Read messages from status_r and collect signatures from it.
 299         When done, reap 'child'.
 300         If there are no signatures, throw SafeException (using errors
 301         for the error message if non-empty)."""
 302         sigs = []
 303
 304         # Should we error out on bad signatures, even if there's a good
 305         # signature too?
 306
 307         for line in status_r:
 308                 assert line.endswith('\n')
 309                 assert line.startswith('[GNUPG:] ')
 310                 line = line[9:-1]
 311                 split_line = line.split(' ')
 312                 code = split_line[0]
 313                 args = split_line[1:]
 314                 if code == 'VALIDSIG':
 315                         sigs.append(ValidSig(args))
 316                 elif code == 'BADSIG':
 317                         sigs.append(BadSig(args))
 318                 elif code == 'ERRSIG':
 319                         sigs.append(ErrSig(args))
 320
 321         status = child.wait()
 322
 323         errors.seek(0)
 324
 325         error_messages = errors.read().strip()
 326         errors.close()
 327
 328         if not sigs:
 329                 if error_messages:
 330                         raise SafeException("No signatures found. Errors from GPG:\n%s" % error_messages)
 331                 else:
 332                         raise SafeException("No signatures found. No error messages from GPG.")
 333
 334         return sigs