src/codesigdb.cpp

   1 /*
   2  * Copyright (c) 2003-2008 Apple Inc. All Rights Reserved.
   3  *
   4  * @APPLE_LICENSE_HEADER_START@
   5  *
   6  * This file contains Original Code and/or Modifications of Original Code
   7  * as defined in and that are subject to the Apple Public Source License
   8  * Version 2.0 (the 'License'). You may not use this file except in
   9  * compliance with the License. Please obtain a copy of the License at
  10  * http://www.opensource.apple.com/apsl/ and read it before using this
  11  * file.
  12  *
  13  * The Original Code and all software distributed under the License are
  14  * distributed on an 'AS IS' basis, WITHOUT WARRANTY OF ANY KIND, EITHER
  15  * EXPRESS OR IMPLIED, AND APPLE HEREBY DISCLAIMS ALL SUCH WARRANTIES,
  16  * INCLUDING WITHOUT LIMITATION, ANY WARRANTIES OF MERCHANTABILITY,
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  18  * Please see the License for the specific language governing rights and
  19  * limitations under the License.
  20  *
  21  * @APPLE_LICENSE_HEADER_END@
  22  */
  23
  24
  25 //
  26 // codesigdb - code-hash equivalence database
  27 //
  28 #include "codesigdb.h"
  29 #include "process.h"
  30 #include "server.h"
  31 #include "agentquery.h"
  32 #include <security_utilities/memutils.h>
  33 #include <security_utilities/logging.h>
  34 #include <Security/SecRequirementPriv.h>
  35
  36
  37 //
  38 // A self-constructing database key class.
  39 // Key format is <t><uid|S><key data>
  40 //  where
  41 // <t> single ASCII character type code ('H' for hash links)
  42 // <uid|S> decimal userid of owning user, or 'S' for system entries. Followed by null byte.
  43 // <key data> variable length key value (binary).
  44 //
  45 class DbKey : public CssmAutoData {
  46 public:
  47         DbKey(char type, const CssmData &key, bool perUser = false, uid_t user = 0);
  48 };
  49
  50 DbKey::DbKey(char type, const CssmData &key, bool perUser, uid_t user)
  51         : CssmAutoData(Allocator::standard())
  52 {
  53         using namespace LowLevelMemoryUtilities;
  54         char header[20];
  55         size_t headerLength;
  56         if (perUser)
  57                 headerLength = 1 + sprintf(header, "%c%d", type, user);
  58         else
  59                 headerLength = 1 + sprintf(header, "%cS", type);
  60         malloc(headerLength + key.length());
  61         memcpy(this->data(), header, headerLength);
  62         memcpy(get().at(headerLength), key.data(), key.length());
  63 }
  64
  65
  66 //
  67 // A subclass of Identity made of whole cloth (from a raw CodeSignature ACL information)
  68 //
  69 struct AclIdentity : public CodeSignatures::Identity {
  70         AclIdentity(const CssmData hash, string path) : mHash(hash), mPath(path) { }
  71
  72         string getPath() const { return mPath; }
  73         const CssmData getHash() const { return mHash; }
  74
  75 private:
  76         const CssmData mHash;
  77         const string mPath;
  78 };
  79
  80
  81 //
  82 // Construct a CodeSignatures objects
  83 //
  84 CodeSignatures::CodeSignatures(const char *path)
  85 {
  86         try {
  87                 mDb.open(path, O_RDWR | O_CREAT, 0644);
  88         } catch (const CommonError &err) {
  89                 try {
  90                         mDb.open(path, O_RDONLY, 0644);
  91                         Syslog::warning("database %s opened READONLY (R/W failed errno=%d)", path, err.unixError());
  92                         secdebug("codesign", "database %s opened READONLY (R/W failed errno=%d)", path, err.unixError());
  93                 } catch (...) {
  94                         Syslog::warning("cannot open %s; using no code equivalents", path);
  95                         secdebug("codesign", "unable to open %s; using no code equivalents", path);
  96                 }
  97         }
  98         if (mDb)
  99                 mDb.flush();    // in case we just created it
 100         IFDUMPING("equiv", debugDump("open"));
 101 }
 102
 103 CodeSignatures::~CodeSignatures()
 104 {
 105 }
 106
 107
 108 //
 109 // (Re)open the equivalence database.
 110 // This is useful to switch to database in another volume.
 111 //
 112 void CodeSignatures::open(const char *path)
 113 {
 114         mDb.open(path, O_RDWR | O_CREAT, 0644);
 115         mDb.flush();
 116         IFDUMPING("equiv", debugDump("reopen"));
 117 }
 118
 119
 120 //
 121 // Basic Identity objects
 122 //
 123 CodeSignatures::Identity::Identity() : mState(untried)
 124 { }
 125
 126 CodeSignatures::Identity::~Identity()
 127 { }
 128
 129 string CodeSignatures::Identity::canonicalName(const string &path)
 130 {
 131         string::size_type slash = path.rfind('/');
 132         if (slash == string::npos)      // bloody unlikely, but whatever...
 133                 return path;
 134         return path.substr(slash+1);
 135 }
 136
 137
 138 //
 139 // Find and store database objects (primitive layer)
 140 //
 141 bool CodeSignatures::find(Identity &id, uid_t user)
 142 {
 143         if (id.mState != Identity::untried)
 144                 return id.mState == Identity::valid;
 145         try {
 146                 DbKey userKey('H', id.getHash(), true, user);
 147                 CssmData linkValue;
 148                 if (mDb.get(userKey, linkValue)) {
 149                         id.mName = string(linkValue.interpretedAs<const char>(), linkValue.length());
 150                         IFDUMPING("equiv", id.debugDump("found/user"));
 151                         id.mState = Identity::valid;
 152                         return true;
 153                 }
 154                 DbKey sysKey('H', id.getHash());
 155                 if (mDb.get(sysKey, linkValue)) {
 156                         id.mName = string(linkValue.interpretedAs<const char>(), linkValue.length());
 157                         IFDUMPING("equiv", id.debugDump("found/system"));
 158                         id.mState = Identity::valid;
 159                         return true;
 160                 }
 161         } catch (...) {
 162                 secdebug("codesign", "exception validating identity for %s - marking failed", id.path().c_str());
 163                 id.mState = Identity::invalid;
 164         }
 165         return id.mState == Identity::valid;
 166 }
 167
 168 void CodeSignatures::makeLink(Identity &id, const string &ident, bool forUser, uid_t user)
 169 {
 170         DbKey key('H', id.getHash(), forUser, user);
 171         if (!mDb.put(key, StringData(ident)))
 172                 UnixError::throwMe();
 173 }
 174
 175
 176 //
 177 // Administrative manipulation calls
 178 //
 179 void CodeSignatures::addLink(const CssmData &oldHash, const CssmData &newHash,
 180         const char *inName, bool forSystem)
 181 {
 182         string name = Identity::canonicalName(inName);
 183         uid_t user = Server::process().uid();
 184         if (forSystem && user)  // only root user can establish forSystem links
 185                 UnixError::throwMe(EACCES);
 186         if (!forSystem) // in fact, for now we don't allow per-user calls at all
 187                 UnixError::throwMe(EACCES);
 188         AclIdentity oldCode(oldHash, name);
 189         AclIdentity newCode(newHash, name);
 190         secdebug("codesign", "addlink for name %s", name.c_str());
 191         StLock<Mutex> _(mDatabaseLock);
 192         if (oldCode) {
 193                 if (oldCode.trustedName() != name) {
 194                         secdebug("codesign", "addlink does not match existing name %s",
 195                                 oldCode.trustedName().c_str());
 196                         MacOSError::throwMe(CSSMERR_CSP_VERIFY_FAILED);
 197                 }
 198         } else {
 199                 makeLink(oldCode, name, !forSystem, user);
 200         }
 201         if (!newCode)
 202                 makeLink(newCode, name, !forSystem, user);
 203         mDb.flush();
 204 }
 205
 206 void CodeSignatures::removeLink(const CssmData &hash, const char *name, bool forSystem)
 207 {
 208         AclIdentity code(hash, name);
 209         uid_t user = Server::process().uid();
 210         if (forSystem && user)  // only root user can remove forSystem links
 211                 UnixError::throwMe(EACCES);
 212         DbKey key('H', hash, !forSystem, user);
 213         StLock<Mutex> _(mDatabaseLock);
 214         mDb.erase(key);
 215         mDb.flush();
 216 }
 217
 218
 219 //
 220 // Verify signature matches.
 221 // This ends up getting called when a CodeSignatureAclSubject is validated.
 222 // The OSXVerifier describes what we require of the client code; the process represents
 223 // the requesting client; and the context gives us access to the ACL and its environment
 224 // in case we want to, well, creatively rewrite it for some reason.
 225 //
 226 bool CodeSignatures::verify(Process &process,
 227         const OSXVerifier &verifier, const AclValidationContext &context)
 228 {
 229         secdebug("codesign", "start verify");
 230
 231         StLock<Mutex> _(process);
 232         SecCodeRef code = process.currentGuest();
 233         if (!code) {
 234                 secdebug("codesign", "no code base: fail");
 235                 return false;
 236         }
 237         if (SecRequirementRef requirement = verifier.requirement()) {
 238                 // If the ACL contains a code signature (requirement), we won't match against unsigned code at all.
 239                 // The legacy hash is ignored (it's for use by pre-Leopard systems).
 240                 secdebug("codesign", "CS requirement present; ignoring legacy hashes");
 241                 Server::active().longTermActivity();
 242                 switch (OSStatus rc = SecCodeCheckValidity(code, kSecCSDefaultFlags, requirement)) {
 243                 case noErr:
 244                         secdebug("codesign", "CS verify passed");
 245                         return true;
 246                 case errSecCSUnsigned:
 247                         secdebug("codesign", "CS verify against unsigned binary failed");
 248                         return false;
 249                 default:
 250                         secdebug("codesign", "CS verify failed OSStatus=%d", int32_t(rc));
 251                         return false;
 252                 }
 253         }
 254         switch (matchSignedClientToLegacyACL(process, code, verifier, context)) {
 255         case noErr:                                             // handled, allow access
 256                 return true;
 257         case errSecCSUnsigned:                  // unsigned client, complete legacy case
 258                 secdebug("codesign", "no CS requirement - using legacy hash");
 259                 return verifyLegacy(process,
 260                         CssmData::wrap(verifier.legacyHash(), SHA1::digestLength),
 261                         verifier.path());
 262         default:                                                // client unsuitable, reject this match
 263                 return false;
 264         }
 265 }
 266
 267
 268 //
 269 // See if we can rewrite the ACL from legacy to Code Signing form without losing too much security.
 270 // Returns true if the present validation should succeed (we probably rewrote the ACL).
 271 // Returns false if the present validation shouldn't succeed based on what we did here (we may still
 272 // have rewritten the ACL, in principle).
 273 //
 274 // Note that these checks add nontrivial overhead to ACL processing. We want to eventually phase
 275 // this out, or at least make it an option that doesn't run all the time - perhaps an "extra legacy
 276 // effort" per-client mode bit.
 277 //
 278 static string trim(string s, char delimiter)
 279 {
 280         string::size_type p = s.rfind(delimiter);
 281         if (p != string::npos)
 282                 s = s.substr(p + 1);
 283         return s;
 284 }
 285
 286 static string trim(string s, char delimiter, string suffix)
 287 {
 288         s = trim(s, delimiter);
 289         int preLength = s.length() - suffix.length();
 290         if (preLength > 0 && s.substr(preLength) == suffix)
 291                 s = s.substr(0, preLength);
 292         return s;
 293 }
 294
 295 OSStatus CodeSignatures::matchSignedClientToLegacyACL(Process &process,
 296         SecCodeRef code, const OSXVerifier &verifier, const AclValidationContext &context)
 297 {
 298         //
 299         // Check whether we seem to be matching a legacy .Mac ACL against a member of the .Mac group
 300         //
 301         if (SecurityServerAcl::looksLikeLegacyDotMac(context)) {
 302                 Server::active().longTermActivity();
 303                 CFRef<SecRequirementRef> dotmac;
 304                 MacOSError::check(SecRequirementCreateGroup(CFSTR("dot-mac"), NULL, kSecCSDefaultFlags, &dotmac.aref()));
 305                 if (SecCodeCheckValidity(code, kSecCSDefaultFlags, dotmac) == noErr) {
 306                         secdebug("codesign", "client is a dot-mac application; update the ACL accordingly");
 307
 308                         // create a suitable AclSubject (this is the above-the-API-line way)
 309                         CFRef<CFDataRef> reqdata;
 310                         MacOSError::check(SecRequirementCopyData(dotmac, kSecCSDefaultFlags, &reqdata.aref()));
 311                         RefPointer<CodeSignatureAclSubject> subject = new CodeSignatureAclSubject(NULL, "group://dot-mac");
 312                         subject->add((const BlobCore *)CFDataGetBytePtr(reqdata));
 313
 314                         // add it to the ACL and pass the access check (we just quite literally did it above)
 315                         SecurityServerAcl::addToStandardACL(context, subject);
 316                         return noErr;
 317                 }
 318         }
 319
 320         //
 321         // Get best names for the ACL (legacy) subject and the (signed) client
 322         //
 323         CFRef<CFDictionaryRef> info;
 324         MacOSError::check(SecCodeCopySigningInformation(code, kSecCSSigningInformation, &info.aref()));
 325         CFStringRef signingIdentity = CFStringRef(CFDictionaryGetValue(info, kSecCodeInfoIdentifier));
 326         if (!signingIdentity)           // unsigned
 327                 return errSecCSUnsigned;
 328
 329         string bundleName;      // client
 330         if (CFDictionaryRef infoList = CFDictionaryRef(CFDictionaryGetValue(info, kSecCodeInfoPList)))
 331                 if (CFStringRef name = CFStringRef(CFDictionaryGetValue(infoList, kCFBundleNameKey)))
 332                         bundleName = trim(cfString(name), '.');
 333         if (bundleName.empty()) // fall back to signing identifier
 334                 bundleName = trim(cfString(signingIdentity), '.');
 335
 336         string aclName = trim(verifier.path(), '/', ".app");    // ACL
 337
 338         secdebug("codesign", "matching signed client \"%s\" against legacy ACL \"%s\"",
 339                 bundleName.c_str(), aclName.c_str());
 340
 341         //
 342         // Check whether we're matching a signed APPLE application against a legacy ACL by the same name
 343         //
 344         if (bundleName == aclName) {
 345                 const unsigned char reqData[] = {               // "anchor apple", version 1 blob, embedded here
 346                         0xfa, 0xde, 0x0c, 0x00, 0x00, 0x00, 0x00, 0x10,
 347                         0x00, 0x00, 0x00, 0x01, 0x00, 0x00, 0x00, 0x03
 348                 };
 349                 CFRef<SecRequirementRef> apple;
 350                 MacOSError::check(SecRequirementCreateWithData(CFTempData(reqData, sizeof(reqData)),
 351                         kSecCSDefaultFlags, &apple.aref()));
 352                 Server::active().longTermActivity();
 353                 switch (OSStatus rc = SecCodeCheckValidity(code, kSecCSDefaultFlags, apple)) {
 354                 case noErr:
 355                         {
 356                                 secdebug("codesign", "withstands strict scrutiny; quietly adding new ACL");
 357                                 RefPointer<OSXCode> wrap = new OSXCodeWrap(code);
 358                                 RefPointer<AclSubject> subject = new CodeSignatureAclSubject(OSXVerifier(wrap));
 359                                 SecurityServerAcl::addToStandardACL(context, subject);
 360                                 return noErr;
 361                         }
 362                 default:
 363                         secdebug("codesign", "validation fails with rc=%d, rejecting", int32_t(rc));
 364                         return rc;
 365                 }
 366                 secdebug("codesign", "does not withstand strict scrutiny; ask the user");
 367                 QueryCodeCheck query;
 368                 query.inferHints(process);
 369                 if (!query(verifier.path().c_str())) {
 370                         secdebug("codesign", "user declined equivalence: cancel the access");
 371                         CssmError::throwMe(CSSM_ERRCODE_USER_CANCELED);
 372                 }
 373                 RefPointer<OSXCode> wrap = new OSXCodeWrap(code);
 374                 RefPointer<AclSubject> subject = new CodeSignatureAclSubject(OSXVerifier(wrap));
 375                 SecurityServerAcl::addToStandardACL(context, subject);
 376                 return noErr;
 377         }
 378
 379         // not close enough to even ask - this can't match
 380         return errSecCSReqFailed;
 381 }
 382
 383
 384 //
 385 // Perform legacy hash verification.
 386 // This is the pre-Leopard (Tiger, Panther) code path. Here we only have legacy hashes
 387 // (called, confusingly, "signatures"), which we're matching against suitably computed
 388 // "signatures" (hashes) on the requesting application. We consult the CodeEquivalenceDatabase
 389 // in a doomed attempt to track changes made to applications through updates, and issue
 390 // equivalence dialogs to users if we have a name match (but hash mismatch). That's all
 391 // there was before Code Signing; and that's what you'll continue to get if the requesting
 392 // application is unsigned. Until we throw the whole mess out altogether, hopefully by
 393 // the Next Big Cat After Leopard.
 394 //
 395 bool CodeSignatures::verifyLegacy(Process &process, const CssmData &signature, string path)
 396 {
 397         // First of all, if the signature directly matches the client's code, we're obviously fine
 398         // we don't even need the database for that...
 399         Identity &clientIdentity = process;
 400         try {
 401                 if (clientIdentity.getHash() == signature) {
 402                         secdebug("codesign", "direct match: pass");
 403                         return true;
 404                 }
 405         } catch (...) {
 406                 secdebug("codesign", "exception getting client code hash: fail");
 407                 return false;
 408         }
 409
 410 #if CONSULT_LEGACY_CODE_EQUIVALENCE_DATABASE
 411
 412         // Ah well. Establish mediator objects for database signature links
 413         AclIdentity aclIdentity(signature, path);
 414
 415         uid_t user = process.uid();
 416         {
 417                 StLock<Mutex> _(mDatabaseLock);
 418                 find(aclIdentity, user);
 419                 find(clientIdentity, user);
 420         }
 421
 422         // if both links exist, we can decide this right now
 423         if (aclIdentity && clientIdentity) {
 424                 if (aclIdentity.trustedName() == clientIdentity.trustedName()) {
 425                         secdebug("codesign", "app references match: pass");
 426                         return true;
 427                 } else {
 428                         secdebug("codesign", "client/acl links exist but are unequal: fail");
 429                         return false;
 430                 }
 431         }
 432
 433         // check for name equality
 434         secdebug("codesign", "matching client %s against acl %s",
 435                 clientIdentity.name().c_str(), aclIdentity.name().c_str());
 436         if (aclIdentity.name() != clientIdentity.name()) {
 437                 secdebug("codesign", "name/path mismatch: fail");
 438                 return false;
 439         }
 440
 441         // The names match - we have a possible update.
 442
 443         // Take the UI lock now to serialize "update rushes".
 444         LongtermStLock uiLocker(mUILock);
 445
 446         // re-read the database in case some other thread beat us to the update
 447         {
 448                 StLock<Mutex> _(mDatabaseLock);
 449                 find(aclIdentity, user);
 450                 find(clientIdentity, user);
 451         }
 452         if (aclIdentity && clientIdentity) {
 453                 if (aclIdentity.trustedName() == clientIdentity.trustedName()) {
 454                         secdebug("codesign", "app references match: pass (on the rematch)");
 455                         return true;
 456                 } else {
 457                         secdebug("codesign", "client/acl links exist but are unequal: fail (on the rematch)");
 458                         return false;
 459                 }
 460         }
 461
 462         // ask the user
 463         QueryCodeCheck query;
 464     query.inferHints(process);
 465         if (!query(aclIdentity.path().c_str()))
 466     {
 467                 secdebug("codesign", "user declined equivalence: cancel the access");
 468                 CssmError::throwMe(CSSM_ERRCODE_USER_CANCELED);
 469         }
 470
 471         // take the database lock back for real
 472         StLock<Mutex> _(mDatabaseLock);
 473
 474         // user wants us to go ahead and establish trust (if possible)
 475         if (aclIdentity) {
 476                 // acl is linked but new client: link the client to this application
 477                 makeLink(clientIdentity, aclIdentity.trustedName(), true, user);
 478                 mDb.flush();
 479                 secdebug("codesign", "client %s linked to application %s: pass",
 480                         clientIdentity.path().c_str(), aclIdentity.trustedName().c_str());
 481                 return true;
 482         }
 483
 484         if (clientIdentity) {   // code link exists, acl link missing
 485                 // client is linked but ACL (hash) never seen: link the ACL to this app
 486                 makeLink(aclIdentity, clientIdentity.trustedName(), true, user);
 487                 mDb.flush();
 488                 secdebug("codesign", "acl %s linked to client %s: pass",
 489                         aclIdentity.path().c_str(), clientIdentity.trustedName().c_str());
 490                 return true;
 491         }
 492
 493         // the De Novo case: no links, must create everything
 494         string ident = clientIdentity.name();
 495         makeLink(clientIdentity, ident, true, user);
 496         makeLink(aclIdentity, ident, true, user);
 497         mDb.flush();
 498         secdebug("codesign", "new linkages established: pass");
 499         return true;
 500
 501 #else /* ignore Code Equivalence Database */
 502
 503         return false;
 504
 505 #endif
 506 }
 507
 508
 509 //
 510 // Debug dumping support
 511 //
 512 #if defined(DEBUGDUMP)
 513
 514 void CodeSignatures::debugDump(const char *how) const
 515 {
 516         using namespace Debug;
 517         using namespace LowLevelMemoryUtilities;
 518         if (!how)
 519                 how = "dump";
 520         CssmData key, value;
 521         if (!mDb.first(key, value)) {
 522                 dump("CODE EQUIVALENTS DATABASE IS EMPTY (%s)\n", how);
 523         } else {
 524                 dump("CODE EQUIVALENTS DATABASE DUMP (%s)\n", how);
 525                 do {
 526                         const char *header = key.interpretedAs<const char>();
 527                         size_t headerLength = strlen(header) + 1;
 528                         dump("%s:", header);
 529                         dumpData(key.at(headerLength), key.length() - headerLength);
 530                         dump(" => ");
 531                         dumpData(value);
 532                         dump("\n");
 533                 } while (mDb.next(key, value));
 534                 dump("END DUMP\n");
 535         }
 536 }
 537
 538 void CodeSignatures::Identity::debugDump(const char *how) const
 539 {
 540         using namespace Debug;
 541         if (!how)
 542                 how = "dump";
 543         dump("IDENTITY (%s) path=%s", how, getPath().c_str());
 544         dump(" name=%s hash=", mName.empty() ? "(unset)" : mName.c_str());
 545         dumpData(getHash());
 546         dump("\n");
 547 }
 548
 549 #endif //DEBUGDUMP