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crypto/x509: enforce path length constraint.
An X.509 path length constrains the number of certificate that may follow in the chain. This is a little simplistic for a first pass as it doesn't check self-signed certificates (which don't count towards the length), but it's conservatively simplistic. R=golang-dev, r CC=golang-dev https://golang.org/cl/5727057
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@ -23,6 +23,9 @@ const (
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// certificate has a name constraint which doesn't include the name
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// being checked.
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CANotAuthorizedForThisName
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// TooManyIntermediates results when a path length constraint is
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// violated.
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TooManyIntermediates
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)
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// CertificateInvalidError results when an odd error occurs. Users of this
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@ -40,6 +43,8 @@ func (e CertificateInvalidError) Error() string {
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return "x509: certificate has expired or is not yet valid"
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case CANotAuthorizedForThisName:
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return "x509: a root or intermediate certificate is not authorized to sign in this domain"
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case TooManyIntermediates:
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return "x509: too many intermediates for path length constraint"
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}
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return "x509: unknown error"
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}
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@ -87,7 +92,7 @@ const (
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)
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// isValid performs validity checks on the c.
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func (c *Certificate) isValid(certType int, opts *VerifyOptions) error {
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func (c *Certificate) isValid(certType int, currentChain []*Certificate, opts *VerifyOptions) error {
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now := opts.CurrentTime
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if now.IsZero() {
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now = time.Now()
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@ -130,6 +135,13 @@ func (c *Certificate) isValid(certType int, opts *VerifyOptions) error {
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return CertificateInvalidError{c, NotAuthorizedToSign}
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}
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if c.BasicConstraintsValid && c.MaxPathLen >= 0 {
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numIntermediates := len(currentChain) - 1
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if numIntermediates > c.MaxPathLen {
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return CertificateInvalidError{c, TooManyIntermediates}
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}
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}
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return nil
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}
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@ -140,7 +152,7 @@ func (c *Certificate) isValid(certType int, opts *VerifyOptions) error {
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//
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// WARNING: this doesn't do any revocation checking.
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func (c *Certificate) Verify(opts VerifyOptions) (chains [][]*Certificate, err error) {
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err = c.isValid(leafCertificate, &opts)
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err = c.isValid(leafCertificate, nil, &opts)
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if err != nil {
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return
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}
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@ -163,7 +175,7 @@ func appendToFreshChain(chain []*Certificate, cert *Certificate) []*Certificate
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func (c *Certificate) buildChains(cache map[int][][]*Certificate, currentChain []*Certificate, opts *VerifyOptions) (chains [][]*Certificate, err error) {
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for _, rootNum := range opts.Roots.findVerifiedParents(c) {
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root := opts.Roots.certs[rootNum]
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err = root.isValid(rootCertificate, opts)
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err = root.isValid(rootCertificate, currentChain, opts)
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if err != nil {
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continue
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}
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@ -178,7 +190,7 @@ nextIntermediate:
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continue nextIntermediate
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}
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}
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err = intermediate.isValid(intermediateCertificate, opts)
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err = intermediate.isValid(intermediateCertificate, currentChain, opts)
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if err != nil {
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continue
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}
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@ -429,7 +429,7 @@ func (h UnhandledCriticalExtension) Error() string {
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type basicConstraints struct {
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IsCA bool `asn1:"optional"`
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MaxPathLen int `asn1:"optional"`
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MaxPathLen int `asn1:"optional,default:-1"`
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}
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// RFC 5280 4.2.1.4
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