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