cert_pool.go

     1  // Copyright 2011 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  	"crypto/sha256"
    10  	"encoding/pem"
    11  	"sync"
    12  )
    13  
    14  type sum224 [sha256.Size224]byte
    15  
    16  // CertPool is a set of certificates.
    17  type CertPool struct {
    18  	byName map[string][]int // cert.RawSubject => index into lazyCerts
    19  
    20  	// lazyCerts contains funcs that return a certificate,
    21  	// lazily parsing/decompressing it as needed.
    22  	lazyCerts []lazyCert
    23  
    24  	// haveSum maps from sum224(cert.Raw) to true. It's used only
    25  	// for AddCert duplicate detection, to avoid CertPool.contains
    26  	// calls in the AddCert path (because the contains method can
    27  	// call getCert and otherwise negate savings from lazy getCert
    28  	// funcs).
    29  	haveSum map[sum224]bool
    30  
    31  	// systemPool indicates whether this is a special pool derived from the
    32  	// system roots. If it includes additional roots, it requires doing two
    33  	// verifications, one using the roots provided by the caller, and one using
    34  	// the system platform verifier.
    35  	systemPool bool
    36  }
    37  
    38  // lazyCert is minimal metadata about a Cert and a func to retrieve it
    39  // in its normal expanded *Certificate form.
    40  type lazyCert struct {
    41  	// rawSubject is the Certificate.RawSubject value.
    42  	// It's the same as the CertPool.byName key, but in []byte
    43  	// form to make CertPool.Subjects (as used by crypto/tls) do
    44  	// fewer allocations.
    45  	rawSubject []byte
    46  
    47  	// getCert returns the certificate.
    48  	//
    49  	// It is not meant to do network operations or anything else
    50  	// where a failure is likely; the func is meant to lazily
    51  	// parse/decompress data that is already known to be good. The
    52  	// error in the signature primarily is meant for use in the
    53  	// case where a cert file existed on local disk when the program
    54  	// started up is deleted later before it's read.
    55  	getCert func() (*Certificate, error)
    56  }
    57  
    58  // NewCertPool returns a new, empty CertPool.
    59  func NewCertPool() *CertPool {
    60  	return &CertPool{
    61  		byName:  make(map[string][]int),
    62  		haveSum: make(map[sum224]bool),
    63  	}
    64  }
    65  
    66  // len returns the number of certs in the set.
    67  // A nil set is a valid empty set.
    68  func (s *CertPool) len() int {
    69  	if s == nil {
    70  		return 0
    71  	}
    72  	return len(s.lazyCerts)
    73  }
    74  
    75  // cert returns cert index n in s.
    76  func (s *CertPool) cert(n int) (*Certificate, error) {
    77  	return s.lazyCerts[n].getCert()
    78  }
    79  
    80  func (s *CertPool) copy() *CertPool {
    81  	p := &CertPool{
    82  		byName:     make(map[string][]int, len(s.byName)),
    83  		lazyCerts:  make([]lazyCert, len(s.lazyCerts)),
    84  		haveSum:    make(map[sum224]bool, len(s.haveSum)),
    85  		systemPool: s.systemPool,
    86  	}
    87  	for k, v := range s.byName {
    88  		indexes := make([]int, len(v))
    89  		copy(indexes, v)
    90  		p.byName[k] = indexes
    91  	}
    92  	for k := range s.haveSum {
    93  		p.haveSum[k] = true
    94  	}
    95  	copy(p.lazyCerts, s.lazyCerts)
    96  	return p
    97  }
    98  
    99  // SystemCertPool returns a copy of the system cert pool.
   100  //
   101  // On Unix systems other than macOS the environment variables SSL_CERT_FILE and
   102  // SSL_CERT_DIR can be used to override the system default locations for the SSL
   103  // certificate file and SSL certificate files directory, respectively. The
   104  // latter can be a colon-separated list.
   105  //
   106  // Any mutations to the returned pool are not written to disk and do not affect
   107  // any other pool returned by SystemCertPool.
   108  //
   109  // New changes in the system cert pool might not be reflected in subsequent calls.
   110  func SystemCertPool() (*CertPool, error) {
   111  	if sysRoots := systemRootsPool(); sysRoots != nil {
   112  		return sysRoots.copy(), nil
   113  	}
   114  
   115  	return loadSystemRoots()
   116  }
   117  
   118  // findPotentialParents returns the indexes of certificates in s which might
   119  // have signed cert.
   120  func (s *CertPool) findPotentialParents(cert *Certificate) []*Certificate {
   121  	if s == nil {
   122  		return nil
   123  	}
   124  
   125  	// consider all candidates where cert.Issuer matches cert.Subject.
   126  	// when picking possible candidates the list is built in the order
   127  	// of match plausibility as to save cycles in buildChains:
   128  	//   AKID and SKID match
   129  	//   AKID present, SKID missing / AKID missing, SKID present
   130  	//   AKID and SKID don't match
   131  	var matchingKeyID, oneKeyID, mismatchKeyID []*Certificate
   132  	for _, c := range s.byName[string(cert.RawIssuer)] {
   133  		candidate, err := s.cert(c)
   134  		if err != nil {
   135  			continue
   136  		}
   137  		kidMatch := bytes.Equal(candidate.SubjectKeyId, cert.AuthorityKeyId)
   138  		switch {
   139  		case kidMatch:
   140  			matchingKeyID = append(matchingKeyID, candidate)
   141  		case (len(candidate.SubjectKeyId) == 0 && len(cert.AuthorityKeyId) > 0) ||
   142  			(len(candidate.SubjectKeyId) > 0 && len(cert.AuthorityKeyId) == 0):
   143  			oneKeyID = append(oneKeyID, candidate)
   144  		default:
   145  			mismatchKeyID = append(mismatchKeyID, candidate)
   146  		}
   147  	}
   148  
   149  	found := len(matchingKeyID) + len(oneKeyID) + len(mismatchKeyID)
   150  	if found == 0 {
   151  		return nil
   152  	}
   153  	candidates := make([]*Certificate, 0, found)
   154  	candidates = append(candidates, matchingKeyID...)
   155  	candidates = append(candidates, oneKeyID...)
   156  	candidates = append(candidates, mismatchKeyID...)
   157  	return candidates
   158  }
   159  
   160  func (s *CertPool) contains(cert *Certificate) bool {
   161  	if s == nil {
   162  		return false
   163  	}
   164  	return s.haveSum[sha256.Sum224(cert.Raw)]
   165  }
   166  
   167  // AddCert adds a certificate to a pool.
   168  func (s *CertPool) AddCert(cert *Certificate) {
   169  	if cert == nil {
   170  		panic("adding nil Certificate to CertPool")
   171  	}
   172  	s.addCertFunc(sha256.Sum224(cert.Raw), string(cert.RawSubject), func() (*Certificate, error) {
   173  		return cert, nil
   174  	})
   175  }
   176  
   177  // addCertFunc adds metadata about a certificate to a pool, along with
   178  // a func to fetch that certificate later when needed.
   179  //
   180  // The rawSubject is Certificate.RawSubject and must be non-empty.
   181  // The getCert func may be called 0 or more times.
   182  func (s *CertPool) addCertFunc(rawSum224 sum224, rawSubject string, getCert func() (*Certificate, error)) {
   183  	if getCert == nil {
   184  		panic("getCert can't be nil")
   185  	}
   186  
   187  	// Check that the certificate isn't being added twice.
   188  	if s.haveSum[rawSum224] {
   189  		return
   190  	}
   191  
   192  	s.haveSum[rawSum224] = true
   193  	s.lazyCerts = append(s.lazyCerts, lazyCert{
   194  		rawSubject: []byte(rawSubject),
   195  		getCert:    getCert,
   196  	})
   197  	s.byName[rawSubject] = append(s.byName[rawSubject], len(s.lazyCerts)-1)
   198  }
   199  
   200  // AppendCertsFromPEM attempts to parse a series of PEM encoded certificates.
   201  // It appends any certificates found to s and reports whether any certificates
   202  // were successfully parsed.
   203  //
   204  // On many Linux systems, /etc/ssl/cert.pem will contain the system wide set
   205  // of root CAs in a format suitable for this function.
   206  func (s *CertPool) AppendCertsFromPEM(pemCerts []byte) (ok bool) {
   207  	for len(pemCerts) > 0 {
   208  		var block *pem.Block
   209  		block, pemCerts = pem.Decode(pemCerts)
   210  		if block == nil {
   211  			break
   212  		}
   213  		if block.Type != "CERTIFICATE" || len(block.Headers) != 0 {
   214  			continue
   215  		}
   216  
   217  		certBytes := block.Bytes
   218  		cert, err := ParseCertificate(certBytes)
   219  		if err != nil {
   220  			continue
   221  		}
   222  		var lazyCert struct {
   223  			sync.Once
   224  			v *Certificate
   225  		}
   226  		s.addCertFunc(sha256.Sum224(cert.Raw), string(cert.RawSubject), func() (*Certificate, error) {
   227  			lazyCert.Do(func() {
   228  				// This can't fail, as the same bytes already parsed above.
   229  				lazyCert.v, _ = ParseCertificate(certBytes)
   230  				certBytes = nil
   231  			})
   232  			return lazyCert.v, nil
   233  		})
   234  		ok = true
   235  	}
   236  
   237  	return ok
   238  }
   239  
   240  // Subjects returns a list of the DER-encoded subjects of
   241  // all of the certificates in the pool.
   242  //
   243  // Deprecated: if s was returned by SystemCertPool, Subjects
   244  // will not include the system roots.
   245  func (s *CertPool) Subjects() [][]byte {
   246  	res := make([][]byte, s.len())
   247  	for i, lc := range s.lazyCerts {
   248  		res[i] = lc.rawSubject
   249  	}
   250  	return res
   251  }
   252
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