root_windows.go

     1  // Copyright 2012 The Go Authors. All rights reserved.
     2  // Use of this source code is governed by a BSD-style
     3  // license that can be found in the LICENSE file.
     4  
     5  package x509
     6  
     7  import (
     8  	"bytes"
     9  	"errors"
    10  	"strings"
    11  	"syscall"
    12  	"unsafe"
    13  )
    14  
    15  func loadSystemRoots() (*CertPool, error) {
    16  	return &CertPool{systemPool: true}, nil
    17  }
    18  
    19  // Creates a new *syscall.CertContext representing the leaf certificate in an in-memory
    20  // certificate store containing itself and all of the intermediate certificates specified
    21  // in the opts.Intermediates CertPool.
    22  //
    23  // A pointer to the in-memory store is available in the returned CertContext's Store field.
    24  // The store is automatically freed when the CertContext is freed using
    25  // syscall.CertFreeCertificateContext.
    26  func createStoreContext(leaf *Certificate, opts *VerifyOptions) (*syscall.CertContext, error) {
    27  	var storeCtx *syscall.CertContext
    28  
    29  	leafCtx, err := syscall.CertCreateCertificateContext(syscall.X509_ASN_ENCODING|syscall.PKCS_7_ASN_ENCODING, &leaf.Raw[0], uint32(len(leaf.Raw)))
    30  	if err != nil {
    31  		return nil, err
    32  	}
    33  	defer syscall.CertFreeCertificateContext(leafCtx)
    34  
    35  	handle, err := syscall.CertOpenStore(syscall.CERT_STORE_PROV_MEMORY, 0, 0, syscall.CERT_STORE_DEFER_CLOSE_UNTIL_LAST_FREE_FLAG, 0)
    36  	if err != nil {
    37  		return nil, err
    38  	}
    39  	defer syscall.CertCloseStore(handle, 0)
    40  
    41  	err = syscall.CertAddCertificateContextToStore(handle, leafCtx, syscall.CERT_STORE_ADD_ALWAYS, &storeCtx)
    42  	if err != nil {
    43  		return nil, err
    44  	}
    45  
    46  	if opts.Intermediates != nil {
    47  		for i := 0; i < opts.Intermediates.len(); i++ {
    48  			intermediate, _, err := opts.Intermediates.cert(i)
    49  			if err != nil {
    50  				return nil, err
    51  			}
    52  			ctx, err := syscall.CertCreateCertificateContext(syscall.X509_ASN_ENCODING|syscall.PKCS_7_ASN_ENCODING, &intermediate.Raw[0], uint32(len(intermediate.Raw)))
    53  			if err != nil {
    54  				return nil, err
    55  			}
    56  
    57  			err = syscall.CertAddCertificateContextToStore(handle, ctx, syscall.CERT_STORE_ADD_ALWAYS, nil)
    58  			syscall.CertFreeCertificateContext(ctx)
    59  			if err != nil {
    60  				return nil, err
    61  			}
    62  		}
    63  	}
    64  
    65  	return storeCtx, nil
    66  }
    67  
    68  // extractSimpleChain extracts the final certificate chain from a CertSimpleChain.
    69  func extractSimpleChain(simpleChain **syscall.CertSimpleChain, count int) (chain []*Certificate, err error) {
    70  	if simpleChain == nil || count == 0 {
    71  		return nil, errors.New("x509: invalid simple chain")
    72  	}
    73  
    74  	simpleChains := unsafe.Slice(simpleChain, count)
    75  	lastChain := simpleChains[count-1]
    76  	elements := unsafe.Slice(lastChain.Elements, lastChain.NumElements)
    77  	for i := 0; i < int(lastChain.NumElements); i++ {
    78  		// Copy the buf, since ParseCertificate does not create its own copy.
    79  		cert := elements[i].CertContext
    80  		encodedCert := unsafe.Slice(cert.EncodedCert, cert.Length)
    81  		buf := bytes.Clone(encodedCert)
    82  		parsedCert, err := ParseCertificate(buf)
    83  		if err != nil {
    84  			return nil, err
    85  		}
    86  		chain = append(chain, parsedCert)
    87  	}
    88  
    89  	return chain, nil
    90  }
    91  
    92  // checkChainTrustStatus checks the trust status of the certificate chain, translating
    93  // any errors it finds into Go errors in the process.
    94  func checkChainTrustStatus(c *Certificate, chainCtx *syscall.CertChainContext) error {
    95  	if chainCtx.TrustStatus.ErrorStatus != syscall.CERT_TRUST_NO_ERROR {
    96  		status := chainCtx.TrustStatus.ErrorStatus
    97  		switch status {
    98  		case syscall.CERT_TRUST_IS_NOT_TIME_VALID:
    99  			return CertificateInvalidError{c, Expired, ""}
   100  		case syscall.CERT_TRUST_IS_NOT_VALID_FOR_USAGE:
   101  			return CertificateInvalidError{c, IncompatibleUsage, ""}
   102  		// TODO(filippo): surface more error statuses.
   103  		default:
   104  			return UnknownAuthorityError{c, nil, nil}
   105  		}
   106  	}
   107  	return nil
   108  }
   109  
   110  // checkChainSSLServerPolicy checks that the certificate chain in chainCtx is valid for
   111  // use as a certificate chain for a SSL/TLS server.
   112  func checkChainSSLServerPolicy(c *Certificate, chainCtx *syscall.CertChainContext, opts *VerifyOptions) error {
   113  	servernamep, err := syscall.UTF16PtrFromString(strings.TrimSuffix(opts.DNSName, "."))
   114  	if err != nil {
   115  		return err
   116  	}
   117  	sslPara := &syscall.SSLExtraCertChainPolicyPara{
   118  		AuthType:   syscall.AUTHTYPE_SERVER,
   119  		ServerName: servernamep,
   120  	}
   121  	sslPara.Size = uint32(unsafe.Sizeof(*sslPara))
   122  
   123  	para := &syscall.CertChainPolicyPara{
   124  		ExtraPolicyPara: (syscall.Pointer)(unsafe.Pointer(sslPara)),
   125  	}
   126  	para.Size = uint32(unsafe.Sizeof(*para))
   127  
   128  	status := syscall.CertChainPolicyStatus{}
   129  	err = syscall.CertVerifyCertificateChainPolicy(syscall.CERT_CHAIN_POLICY_SSL, chainCtx, para, &status)
   130  	if err != nil {
   131  		return err
   132  	}
   133  
   134  	// TODO(mkrautz): use the lChainIndex and lElementIndex fields
   135  	// of the CertChainPolicyStatus to provide proper context, instead
   136  	// using c.
   137  	if status.Error != 0 {
   138  		switch status.Error {
   139  		case syscall.CERT_E_EXPIRED:
   140  			return CertificateInvalidError{c, Expired, ""}
   141  		case syscall.CERT_E_CN_NO_MATCH:
   142  			return HostnameError{c, opts.DNSName}
   143  		case syscall.CERT_E_UNTRUSTEDROOT:
   144  			return UnknownAuthorityError{c, nil, nil}
   145  		default:
   146  			return UnknownAuthorityError{c, nil, nil}
   147  		}
   148  	}
   149  
   150  	return nil
   151  }
   152  
   153  // windowsExtKeyUsageOIDs are the C NUL-terminated string representations of the
   154  // OIDs for use with the Windows API.
   155  var windowsExtKeyUsageOIDs = make(map[ExtKeyUsage][]byte, len(extKeyUsageOIDs))
   156  
   157  func init() {
   158  	for _, eku := range extKeyUsageOIDs {
   159  		windowsExtKeyUsageOIDs[eku.extKeyUsage] = []byte(eku.oid.String() + "\x00")
   160  	}
   161  }
   162  
   163  func verifyChain(c *Certificate, chainCtx *syscall.CertChainContext, opts *VerifyOptions) (chain []*Certificate, err error) {
   164  	err = checkChainTrustStatus(c, chainCtx)
   165  	if err != nil {
   166  		return nil, err
   167  	}
   168  
   169  	if opts != nil && len(opts.DNSName) > 0 {
   170  		err = checkChainSSLServerPolicy(c, chainCtx, opts)
   171  		if err != nil {
   172  			return nil, err
   173  		}
   174  	}
   175  
   176  	chain, err = extractSimpleChain(chainCtx.Chains, int(chainCtx.ChainCount))
   177  	if err != nil {
   178  		return nil, err
   179  	}
   180  	if len(chain) == 0 {
   181  		return nil, errors.New("x509: internal error: system verifier returned an empty chain")
   182  	}
   183  
   184  	// Mitigate CVE-2020-0601, where the Windows system verifier might be
   185  	// tricked into using custom curve parameters for a trusted root, by
   186  	// double-checking all ECDSA signatures. If the system was tricked into
   187  	// using spoofed parameters, the signature will be invalid for the correct
   188  	// ones we parsed. (We don't support custom curves ourselves.)
   189  	for i, parent := range chain[1:] {
   190  		if parent.PublicKeyAlgorithm != ECDSA {
   191  			continue
   192  		}
   193  		if err := parent.CheckSignature(chain[i].SignatureAlgorithm,
   194  			chain[i].RawTBSCertificate, chain[i].Signature); err != nil {
   195  			return nil, err
   196  		}
   197  	}
   198  	return chain, nil
   199  }
   200  
   201  // systemVerify is like Verify, except that it uses CryptoAPI calls
   202  // to build certificate chains and verify them.
   203  func (c *Certificate) systemVerify(opts *VerifyOptions) (chains [][]*Certificate, err error) {
   204  	storeCtx, err := createStoreContext(c, opts)
   205  	if err != nil {
   206  		return nil, err
   207  	}
   208  	defer syscall.CertFreeCertificateContext(storeCtx)
   209  
   210  	para := new(syscall.CertChainPara)
   211  	para.Size = uint32(unsafe.Sizeof(*para))
   212  
   213  	keyUsages := opts.KeyUsages
   214  	if len(keyUsages) == 0 {
   215  		keyUsages = []ExtKeyUsage{ExtKeyUsageServerAuth}
   216  	}
   217  	oids := make([]*byte, 0, len(keyUsages))
   218  	for _, eku := range keyUsages {
   219  		if eku == ExtKeyUsageAny {
   220  			oids = nil
   221  			break
   222  		}
   223  		if oid, ok := windowsExtKeyUsageOIDs[eku]; ok {
   224  			oids = append(oids, &oid[0])
   225  		}
   226  	}
   227  	if oids != nil {
   228  		para.RequestedUsage.Type = syscall.USAGE_MATCH_TYPE_OR
   229  		para.RequestedUsage.Usage.Length = uint32(len(oids))
   230  		para.RequestedUsage.Usage.UsageIdentifiers = &oids[0]
   231  	} else {
   232  		para.RequestedUsage.Type = syscall.USAGE_MATCH_TYPE_AND
   233  		para.RequestedUsage.Usage.Length = 0
   234  		para.RequestedUsage.Usage.UsageIdentifiers = nil
   235  	}
   236  
   237  	var verifyTime *syscall.Filetime
   238  	if opts != nil && !opts.CurrentTime.IsZero() {
   239  		ft := syscall.NsecToFiletime(opts.CurrentTime.UnixNano())
   240  		verifyTime = &ft
   241  	}
   242  
   243  	// The default is to return only the highest quality chain,
   244  	// setting this flag will add additional lower quality contexts.
   245  	// These are returned in the LowerQualityChains field.
   246  	const CERT_CHAIN_RETURN_LOWER_QUALITY_CONTEXTS = 0x00000080
   247  
   248  	// CertGetCertificateChain will traverse Windows's root stores in an attempt to build a verified certificate chain
   249  	var topCtx *syscall.CertChainContext
   250  	err = syscall.CertGetCertificateChain(syscall.Handle(0), storeCtx, verifyTime, storeCtx.Store, para, CERT_CHAIN_RETURN_LOWER_QUALITY_CONTEXTS, 0, &topCtx)
   251  	if err != nil {
   252  		return nil, err
   253  	}
   254  	defer syscall.CertFreeCertificateChain(topCtx)
   255  
   256  	chain, topErr := verifyChain(c, topCtx, opts)
   257  	if topErr == nil {
   258  		chains = append(chains, chain)
   259  	}
   260  
   261  	if lqCtxCount := topCtx.LowerQualityChainCount; lqCtxCount > 0 {
   262  		lqCtxs := unsafe.Slice(topCtx.LowerQualityChains, lqCtxCount)
   263  		for _, ctx := range lqCtxs {
   264  			chain, err := verifyChain(c, ctx, opts)
   265  			if err == nil {
   266  				chains = append(chains, chain)
   267  			}
   268  		}
   269  	}
   270  
   271  	if len(chains) == 0 {
   272  		// Return the error from the highest quality context.
   273  		return nil, topErr
   274  	}
   275  
   276  	return chains, nil
   277  }
   278
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