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) 2006, Thomas Leonard
  10 # See the README file for details, or visit http://0install.net.
  11
  12 import base64, re
  13 import os
  14 import tempfile
  15 import traceback
  16 from trust import trust_db
  17 from model import SafeException
  18
  19 class Signature(object):
  20         """Abstract base class for signature check results."""
  21         status = None
  22
  23         def __init__(self, status):
  24                 self.status = status
  25
  26         def is_trusted(self, domain = None):
  27                 return False
  28
  29         def need_key(self):
  30                 """Returns the ID of the key that must be downloaded to check this signature."""
  31                 return None
  32
  33 class ValidSig(Signature):
  34         """A valid signature check result."""
  35         FINGERPRINT = 0
  36         TIMESTAMP = 2
  37
  38         def __str__(self):
  39                 return "Valid signature from " + self.status[self.FINGERPRINT]
  40
  41         def is_trusted(self, domain = None):
  42                 return trust_db.is_trusted(self.status[self.FINGERPRINT], domain)
  43
  44         def get_timestamp(self):
  45                 return int(self.status[self.TIMESTAMP])
  46
  47         fingerprint = property(lambda self: self.status[self.FINGERPRINT])
  48
  49         def get_details(self):
  50                 cin, cout = os.popen2(('gpg', '--with-colons', '--no-secmem-warning', '--list-keys', self.fingerprint))
  51                 cin.close()
  52                 details = []
  53                 for line in cout:
  54                         details.append(line.split(':'))
  55                 cout.close()
  56                 return details
  57
  58 class BadSig(Signature):
  59         """A bad signature (doesn't match the message)."""
  60         KEYID = 0
  61
  62         def __str__(self):
  63                 return "BAD signature by " + self.status[self.KEYID] + \
  64                         " (the message has been tampered with)"
  65
  66 class ErrSig(Signature):
  67         """Error while checking a signature."""
  68         KEYID = 0
  69         ALG = 1
  70         RC = -1
  71
  72         def __str__(self):
  73                 msg = "ERROR signature by %s: " % self.status[self.KEYID]
  74                 rc = int(self.status[self.RC])
  75                 if rc == 4:
  76                         msg += "Unknown or unsupported algorithm '%s'" % self.status[self.ALG]
  77                 elif rc == 9:
  78                         msg += "Unknown key. Try 'gpg --recv-key %s'" % self.status[self.KEYID]
  79                 else:
  80                         msg += "Unknown reason code %d" % rc
  81                 return msg
  82
  83         def need_key(self):
  84                 rc = int(self.status[self.RC])
  85                 if rc == 9:
  86                         return self.status[self.KEYID]
  87                 return None
  88
  89 class Key:
  90         """A GPG key.
  91         @since: 0.27
  92         """
  93         def __init__(self, fingerprint):
  94                 self.fingerprint = fingerprint
  95                 self.name = '(unknown)'
  96
  97         def get_short_name(self):
  98                 return self.name.split(' (', 1)[0].split(' <', 1)[0]
  99
 100 def load_keys(fingerprints):
 101         """Load a set of keys at once.
 102         This is much more efficient than making individual calls to L{load_key}.
 103         @return: a list of loaded keys, indexed by fingerprint
 104         @rtype: {str: L{Key}}
 105         @since 0.27"""
 106
 107         keys = {}
 108
 109         # Otherwise GnuPG returns everything...
 110         if not fingerprints: return keys
 111
 112         for fp in fingerprints:
 113                 keys[fp] = Key(fp)
 114
 115         current_fpr = None
 116         current_uid = None
 117
 118         cin, cout = os.popen2(['gpg', '--fixed-list-mode', '--with-colons', '--list-keys',
 119                                 '--with-fingerprint', '--with-fingerprint'] + fingerprints)
 120         cin.close()
 121         try:
 122                 for line in cout:
 123                         if line.startswith('pub:'):
 124                                 current_fpr = None
 125                                 current_uid = None
 126                         if line.startswith('fpr:'):
 127                                 current_fpr = line.split(':')[9]
 128                                 if current_fpr in keys and current_uid:
 129                                         # This is probably a subordinate key, where the fingerprint
 130                                         # comes after the uid, not before. Note: we assume the subkey is
 131                                         # cross-certified, as recent always ones are.
 132                                         keys[current_fpr].name = current_uid
 133                         if line.startswith('uid:'):
 134                                 assert current_fpr is not None
 135                                 parts = line.split(':')
 136                                 current_uid = parts[9]
 137                                 if current_fpr in keys:
 138                                         keys[current_fpr].name = current_uid
 139         finally:
 140                 cout.close()
 141
 142         return keys
 143
 144 def load_key(fingerprint):
 145         """Query gpg for information about this key.
 146         @return: a new key
 147         @rtype: L{Key}
 148         @since: 0.27"""
 149         return load_keys([fingerprint])[fingerprint]
 150
 151 def import_key(stream):
 152         """Run C{gpg --import} with this stream as stdin."""
 153         errors = tempfile.TemporaryFile()
 154
 155         child = os.fork()
 156         if child == 0:
 157                 # We are the child
 158                 try:
 159                         try:
 160                                 os.dup2(stream.fileno(), 0)
 161                                 os.dup2(errors.fileno(), 2)
 162                                 os.execlp('gpg', 'gpg', '--no-secmem-warning', '--quiet', '--import')
 163                         except:
 164                                 traceback.print_exc()
 165                 finally:
 166                         os._exit(1)
 167                 assert False
 168
 169         pid, status = os.waitpid(child, 0)
 170         assert pid == child
 171
 172         errors.seek(0)
 173         error_messages = errors.read().strip()
 174         errors.close()
 175
 176         if error_messages:
 177                 raise SafeException("Errors from 'gpg --import':\n%s" % error_messages)
 178
 179 def _check_plain_stream(stream):
 180         data = tempfile.TemporaryFile() # Python2.2 does not support 'prefix'
 181         errors = tempfile.TemporaryFile()
 182
 183         status_r, status_w = os.pipe()
 184
 185         child = os.fork()
 186
 187         if child == 0:
 188                 # We are the child
 189                 try:
 190                         try:
 191                                 os.close(status_r)
 192                                 os.dup2(stream.fileno(), 0)
 193                                 os.dup2(data.fileno(), 1)
 194                                 os.dup2(errors.fileno(), 2)
 195                                 os.execlp('gpg', 'gpg', '--no-secmem-warning', '--decrypt',
 196                                            # Not all versions support this:
 197                                            #'--max-output', str(1024 * 1024),
 198                                            '--batch',
 199                                            '--status-fd', str(status_w))
 200                         except:
 201                                 traceback.print_exc()
 202                 finally:
 203                         os._exit(1)
 204                 assert False
 205
 206         # We are the parent
 207         os.close(status_w)
 208
 209         try:
 210                 sigs = _get_sigs_from_gpg_status_stream(status_r, child, errors)
 211         finally:
 212                 data.seek(0)
 213         return (data, sigs)
 214
 215 def _check_xml_stream(stream):
 216         xml_comment_start = '<!-- Base64 Signature'
 217
 218         data_to_check = stream.read()
 219
 220         last_comment = data_to_check.rfind('\n' + xml_comment_start)
 221         if last_comment < 0:
 222                 raise SafeException("No signature block in XML. Maybe this file isn't signed?")
 223         last_comment += 1       # Include new-line in data
 224
 225         data = tempfile.TemporaryFile()
 226         data.write(data_to_check[:last_comment])
 227         data.flush()
 228         os.lseek(data.fileno(), 0, 0)
 229
 230         errors = tempfile.TemporaryFile()
 231
 232         sig_lines = data_to_check[last_comment:].split('\n')
 233         if sig_lines[0].strip() != xml_comment_start:
 234                 raise SafeException('Bad signature block: extra data on comment line')
 235         while sig_lines and not sig_lines[-1].strip():
 236                 del sig_lines[-1]
 237         if sig_lines[-1].strip() != '-->':
 238                 raise SafeException('Bad signature block: last line is not end-of-comment')
 239         sig_data = '\n'.join(sig_lines[1:-1])
 240
 241         if re.match('^[ A-Za-z0-9+/=\n]+$', sig_data) is None:
 242                 raise SafeException("Invalid characters found in base 64 encoded signature")
 243         try:
 244                 sig_data = base64.decodestring(sig_data) # (b64decode is Python 2.4)
 245         except Exception, ex:
 246                 raise SafeException("Invalid base 64 encoded signature: " + str(ex))
 247
 248         sig_fd, sig_name = tempfile.mkstemp(prefix = 'injector-sig-')
 249         try:
 250                 sig_file = os.fdopen(sig_fd, 'w')
 251                 sig_file.write(sig_data)
 252                 sig_file.close()
 253
 254                 status_r, status_w = os.pipe()
 255
 256                 child = os.fork()
 257
 258                 if child == 0:
 259                         # We are the child
 260                         try:
 261                                 try:
 262                                         os.close(status_r)
 263                                         os.dup2(data.fileno(), 0)
 264                                         os.dup2(errors.fileno(), 2)
 265                                         os.execlp('gpg', 'gpg', '--no-secmem-warning',
 266                                                    # Not all versions support this:
 267                                                    #'--max-output', str(1024 * 1024),
 268                                                    '--batch',
 269                                                    '--status-fd', str(status_w),
 270                                                    '--verify', sig_name, '-')
 271                                 except:
 272                                         traceback.print_exc()
 273                         finally:
 274                                 os._exit(1)
 275                         assert False
 276
 277                 # We are the parent
 278                 os.close(status_w)
 279
 280                 try:
 281                         sigs = _get_sigs_from_gpg_status_stream(status_r, child, errors)
 282                 finally:
 283                         os.lseek(stream.fileno(), 0, 0)
 284                         stream.seek(0)
 285         finally:
 286                 os.unlink(sig_name)
 287         return (stream, sigs)
 288
 289 def _find_in_path(prog):
 290         for d in os.environ['PATH'].split(':'):
 291                 path = os.path.join(d, prog)
 292                 if os.path.isfile(path):
 293                         return path
 294         return None
 295
 296 def check_stream(stream):
 297         """Pass stream through gpg --decrypt to get the data, the error text,
 298         and a list of signatures (good or bad). If stream starts with "<?xml "
 299         then get the signature from a comment at the end instead (and the returned
 300         data is the original stream). stream must be seekable.
 301         @note: Stream returned may or may not be the one passed in. Be careful!
 302         @return: (data_stream, [Signatures])"""
 303         if not _find_in_path('gpg'):
 304                 raise SafeException("GnuPG is not installed ('gpg' not in $PATH). See http://gnupg.org")
 305
 306         #stream.seek(0)
 307         #all = stream.read()
 308         stream.seek(0)
 309
 310         start = stream.read(6)
 311         stream.seek(0)
 312         if start == "<?xml ":
 313                 return _check_xml_stream(stream)
 314         elif start == '-----B':
 315                 import warnings
 316                 warnings.warn("Plain GPG-signed feeds are deprecated!", DeprecationWarning, stacklevel = 2)
 317                 os.lseek(stream.fileno(), 0, 0)
 318                 return _check_plain_stream(stream)
 319         else:
 320                 raise SafeException("This is not a Zero Install feed! It should be an XML document, but it starts:\n%s" % repr(stream.read(120)))
 321
 322 def _get_sigs_from_gpg_status_stream(status_r, child, errors):
 323         """Read messages from status_r and collect signatures from it.
 324         When done, reap 'child'.
 325         If there are no signatures, throw SafeException (using errors
 326         for the error message if non-empty)."""
 327         sigs = []
 328
 329         # Should we error out on bad signatures, even if there's a good
 330         # signature too?
 331
 332         for line in os.fdopen(status_r):
 333                 assert line.endswith('\n')
 334                 assert line.startswith('[GNUPG:] ')
 335                 line = line[9:-1]
 336                 split_line = line.split(' ')
 337                 code = split_line[0]
 338                 args = split_line[1:]
 339                 if code == 'VALIDSIG':
 340                         sigs.append(ValidSig(args))
 341                 elif code == 'BADSIG':
 342                         sigs.append(BadSig(args))
 343                 elif code == 'ERRSIG':
 344                         sigs.append(ErrSig(args))
 345
 346         pid, status = os.waitpid(child, 0)
 347         assert pid == child
 348
 349         errors.seek(0)
 350
 351         error_messages = errors.read().strip()
 352         errors.close()
 353
 354         if not sigs:
 355                 if error_messages:
 356                         raise SafeException("No signatures found. Errors from GPG:\n%s" % error_messages)
 357                 else:
 358                         raise SafeException("No signatures found. No error messages from GPG.")
 359
 360         return sigs