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Diffstat (limited to 'src/crypto/x509/verify.go')
| -rw-r--r-- | src/crypto/x509/verify.go | 1176 |
1 files changed, 1176 insertions, 0 deletions
diff --git a/src/crypto/x509/verify.go b/src/crypto/x509/verify.go new file mode 100644 index 0000000..56a1a17 --- /dev/null +++ b/src/crypto/x509/verify.go @@ -0,0 +1,1176 @@ +// Copyright 2011 The Go Authors. All rights reserved. +// Use of this source code is governed by a BSD-style +// license that can be found in the LICENSE file. + +package x509 + +import ( + "bytes" + "crypto" + "crypto/x509/pkix" + "errors" + "fmt" + "net" + "net/url" + "reflect" + "runtime" + "strings" + "time" + "unicode/utf8" +) + +type InvalidReason int + +const ( + // NotAuthorizedToSign results when a certificate is signed by another + // which isn't marked as a CA certificate. + NotAuthorizedToSign InvalidReason = iota + // Expired results when a certificate has expired, based on the time + // given in the VerifyOptions. + Expired + // CANotAuthorizedForThisName results when an intermediate or root + // certificate has a name constraint which doesn't permit a DNS or + // other name (including IP address) in the leaf certificate. + CANotAuthorizedForThisName + // TooManyIntermediates results when a path length constraint is + // violated. + TooManyIntermediates + // IncompatibleUsage results when the certificate's key usage indicates + // that it may only be used for a different purpose. + IncompatibleUsage + // NameMismatch results when the subject name of a parent certificate + // does not match the issuer name in the child. + NameMismatch + // NameConstraintsWithoutSANs is a legacy error and is no longer returned. + NameConstraintsWithoutSANs + // UnconstrainedName results when a CA certificate contains permitted + // name constraints, but leaf certificate contains a name of an + // unsupported or unconstrained type. + UnconstrainedName + // TooManyConstraints results when the number of comparison operations + // needed to check a certificate exceeds the limit set by + // VerifyOptions.MaxConstraintComparisions. This limit exists to + // prevent pathological certificates can consuming excessive amounts of + // CPU time to verify. + TooManyConstraints + // CANotAuthorizedForExtKeyUsage results when an intermediate or root + // certificate does not permit a requested extended key usage. + CANotAuthorizedForExtKeyUsage +) + +// CertificateInvalidError results when an odd error occurs. Users of this +// library probably want to handle all these errors uniformly. +type CertificateInvalidError struct { + Cert *Certificate + Reason InvalidReason + Detail string +} + +func (e CertificateInvalidError) Error() string { + switch e.Reason { + case NotAuthorizedToSign: + return "x509: certificate is not authorized to sign other certificates" + case Expired: + return "x509: certificate has expired or is not yet valid: " + e.Detail + case CANotAuthorizedForThisName: + return "x509: a root or intermediate certificate is not authorized to sign for this name: " + e.Detail + case CANotAuthorizedForExtKeyUsage: + return "x509: a root or intermediate certificate is not authorized for an extended key usage: " + e.Detail + case TooManyIntermediates: + return "x509: too many intermediates for path length constraint" + case IncompatibleUsage: + return "x509: certificate specifies an incompatible key usage" + case NameMismatch: + return "x509: issuer name does not match subject from issuing certificate" + case NameConstraintsWithoutSANs: + return "x509: issuer has name constraints but leaf doesn't have a SAN extension" + case UnconstrainedName: + return "x509: issuer has name constraints but leaf contains unknown or unconstrained name: " + e.Detail + } + return "x509: unknown error" +} + +// HostnameError results when the set of authorized names doesn't match the +// requested name. +type HostnameError struct { + Certificate *Certificate + Host string +} + +func (h HostnameError) Error() string { + c := h.Certificate + + if !c.hasSANExtension() && matchHostnames(c.Subject.CommonName, h.Host) { + return "x509: certificate relies on legacy Common Name field, use SANs instead" + } + + var valid string + if ip := net.ParseIP(h.Host); ip != nil { + // Trying to validate an IP + if len(c.IPAddresses) == 0 { + return "x509: cannot validate certificate for " + h.Host + " because it doesn't contain any IP SANs" + } + for _, san := range c.IPAddresses { + if len(valid) > 0 { + valid += ", " + } + valid += san.String() + } + } else { + valid = strings.Join(c.DNSNames, ", ") + } + + if len(valid) == 0 { + return "x509: certificate is not valid for any names, but wanted to match " + h.Host + } + return "x509: certificate is valid for " + valid + ", not " + h.Host +} + +// UnknownAuthorityError results when the certificate issuer is unknown +type UnknownAuthorityError struct { + Cert *Certificate + // hintErr contains an error that may be helpful in determining why an + // authority wasn't found. + hintErr error + // hintCert contains a possible authority certificate that was rejected + // because of the error in hintErr. + hintCert *Certificate +} + +func (e UnknownAuthorityError) Error() string { + s := "x509: certificate signed by unknown authority" + if e.hintErr != nil { + certName := e.hintCert.Subject.CommonName + if len(certName) == 0 { + if len(e.hintCert.Subject.Organization) > 0 { + certName = e.hintCert.Subject.Organization[0] + } else { + certName = "serial:" + e.hintCert.SerialNumber.String() + } + } + s += fmt.Sprintf(" (possibly because of %q while trying to verify candidate authority certificate %q)", e.hintErr, certName) + } + return s +} + +// SystemRootsError results when we fail to load the system root certificates. +type SystemRootsError struct { + Err error +} + +func (se SystemRootsError) Error() string { + msg := "x509: failed to load system roots and no roots provided" + if se.Err != nil { + return msg + "; " + se.Err.Error() + } + return msg +} + +func (se SystemRootsError) Unwrap() error { return se.Err } + +// errNotParsed is returned when a certificate without ASN.1 contents is +// verified. Platform-specific verification needs the ASN.1 contents. +var errNotParsed = errors.New("x509: missing ASN.1 contents; use ParseCertificate") + +// VerifyOptions contains parameters for Certificate.Verify. +type VerifyOptions struct { + // DNSName, if set, is checked against the leaf certificate with + // Certificate.VerifyHostname or the platform verifier. + DNSName string + + // Intermediates is an optional pool of certificates that are not trust + // anchors, but can be used to form a chain from the leaf certificate to a + // root certificate. + Intermediates *CertPool + // Roots is the set of trusted root certificates the leaf certificate needs + // to chain up to. If nil, the system roots or the platform verifier are used. + Roots *CertPool + + // CurrentTime is used to check the validity of all certificates in the + // chain. If zero, the current time is used. + CurrentTime time.Time + + // KeyUsages specifies which Extended Key Usage values are acceptable. A + // chain is accepted if it allows any of the listed values. An empty list + // means ExtKeyUsageServerAuth. To accept any key usage, include ExtKeyUsageAny. + KeyUsages []ExtKeyUsage + + // MaxConstraintComparisions is the maximum number of comparisons to + // perform when checking a given certificate's name constraints. If + // zero, a sensible default is used. This limit prevents pathological + // certificates from consuming excessive amounts of CPU time when + // validating. It does not apply to the platform verifier. + MaxConstraintComparisions int +} + +const ( + leafCertificate = iota + intermediateCertificate + rootCertificate +) + +// rfc2821Mailbox represents a “mailbox” (which is an email address to most +// people) by breaking it into the “local” (i.e. before the '@') and “domain” +// parts. +type rfc2821Mailbox struct { + local, domain string +} + +// parseRFC2821Mailbox parses an email address into local and domain parts, +// based on the ABNF for a “Mailbox” from RFC 2821. According to RFC 5280, +// Section 4.2.1.6 that's correct for an rfc822Name from a certificate: “The +// format of an rfc822Name is a "Mailbox" as defined in RFC 2821, Section 4.1.2”. +func parseRFC2821Mailbox(in string) (mailbox rfc2821Mailbox, ok bool) { + if len(in) == 0 { + return mailbox, false + } + + localPartBytes := make([]byte, 0, len(in)/2) + + if in[0] == '"' { + // Quoted-string = DQUOTE *qcontent DQUOTE + // non-whitespace-control = %d1-8 / %d11 / %d12 / %d14-31 / %d127 + // qcontent = qtext / quoted-pair + // qtext = non-whitespace-control / + // %d33 / %d35-91 / %d93-126 + // quoted-pair = ("\" text) / obs-qp + // text = %d1-9 / %d11 / %d12 / %d14-127 / obs-text + // + // (Names beginning with “obs-” are the obsolete syntax from RFC 2822, + // Section 4. Since it has been 16 years, we no longer accept that.) + in = in[1:] + QuotedString: + for { + if len(in) == 0 { + return mailbox, false + } + c := in[0] + in = in[1:] + + switch { + case c == '"': + break QuotedString + + case c == '\\': + // quoted-pair + if len(in) == 0 { + return mailbox, false + } + if in[0] == 11 || + in[0] == 12 || + (1 <= in[0] && in[0] <= 9) || + (14 <= in[0] && in[0] <= 127) { + localPartBytes = append(localPartBytes, in[0]) + in = in[1:] + } else { + return mailbox, false + } + + case c == 11 || + c == 12 || + // Space (char 32) is not allowed based on the + // BNF, but RFC 3696 gives an example that + // assumes that it is. Several “verified” + // errata continue to argue about this point. + // We choose to accept it. + c == 32 || + c == 33 || + c == 127 || + (1 <= c && c <= 8) || + (14 <= c && c <= 31) || + (35 <= c && c <= 91) || + (93 <= c && c <= 126): + // qtext + localPartBytes = append(localPartBytes, c) + + default: + return mailbox, false + } + } + } else { + // Atom ("." Atom)* + NextChar: + for len(in) > 0 { + // atext from RFC 2822, Section 3.2.4 + c := in[0] + + switch { + case c == '\\': + // Examples given in RFC 3696 suggest that + // escaped characters can appear outside of a + // quoted string. Several “verified” errata + // continue to argue the point. We choose to + // accept it. + in = in[1:] + if len(in) == 0 { + return mailbox, false + } + fallthrough + + case ('0' <= c && c <= '9') || + ('a' <= c && c <= 'z') || + ('A' <= c && c <= 'Z') || + c == '!' || c == '#' || c == '$' || c == '%' || + c == '&' || c == '\'' || c == '*' || c == '+' || + c == '-' || c == '/' || c == '=' || c == '?' || + c == '^' || c == '_' || c == '`' || c == '{' || + c == '|' || c == '}' || c == '~' || c == '.': + localPartBytes = append(localPartBytes, in[0]) + in = in[1:] + + default: + break NextChar + } + } + + if len(localPartBytes) == 0 { + return mailbox, false + } + + // From RFC 3696, Section 3: + // “period (".") may also appear, but may not be used to start + // or end the local part, nor may two or more consecutive + // periods appear.” + twoDots := []byte{'.', '.'} + if localPartBytes[0] == '.' || + localPartBytes[len(localPartBytes)-1] == '.' || + bytes.Contains(localPartBytes, twoDots) { + return mailbox, false + } + } + + if len(in) == 0 || in[0] != '@' { + return mailbox, false + } + in = in[1:] + + // The RFC species a format for domains, but that's known to be + // violated in practice so we accept that anything after an '@' is the + // domain part. + if _, ok := domainToReverseLabels(in); !ok { + return mailbox, false + } + + mailbox.local = string(localPartBytes) + mailbox.domain = in + return mailbox, true +} + +// domainToReverseLabels converts a textual domain name like foo.example.com to +// the list of labels in reverse order, e.g. ["com", "example", "foo"]. +func domainToReverseLabels(domain string) (reverseLabels []string, ok bool) { + for len(domain) > 0 { + if i := strings.LastIndexByte(domain, '.'); i == -1 { + reverseLabels = append(reverseLabels, domain) + domain = "" + } else { + reverseLabels = append(reverseLabels, domain[i+1:]) + domain = domain[:i] + } + } + + if len(reverseLabels) > 0 && len(reverseLabels[0]) == 0 { + // An empty label at the end indicates an absolute value. + return nil, false + } + + for _, label := range reverseLabels { + if len(label) == 0 { + // Empty labels are otherwise invalid. + return nil, false + } + + for _, c := range label { + if c < 33 || c > 126 { + // Invalid character. + return nil, false + } + } + } + + return reverseLabels, true +} + +func matchEmailConstraint(mailbox rfc2821Mailbox, constraint string) (bool, error) { + // If the constraint contains an @, then it specifies an exact mailbox + // name. + if strings.Contains(constraint, "@") { + constraintMailbox, ok := parseRFC2821Mailbox(constraint) + if !ok { + return false, fmt.Errorf("x509: internal error: cannot parse constraint %q", constraint) + } + return mailbox.local == constraintMailbox.local && strings.EqualFold(mailbox.domain, constraintMailbox.domain), nil + } + + // Otherwise the constraint is like a DNS constraint of the domain part + // of the mailbox. + return matchDomainConstraint(mailbox.domain, constraint) +} + +func matchURIConstraint(uri *url.URL, constraint string) (bool, error) { + // From RFC 5280, Section 4.2.1.10: + // “a uniformResourceIdentifier that does not include an authority + // component with a host name specified as a fully qualified domain + // name (e.g., if the URI either does not include an authority + // component or includes an authority component in which the host name + // is specified as an IP address), then the application MUST reject the + // certificate.” + + host := uri.Host + if len(host) == 0 { + return false, fmt.Errorf("URI with empty host (%q) cannot be matched against constraints", uri.String()) + } + + if strings.Contains(host, ":") && !strings.HasSuffix(host, "]") { + var err error + host, _, err = net.SplitHostPort(uri.Host) + if err != nil { + return false, err + } + } + + if strings.HasPrefix(host, "[") && strings.HasSuffix(host, "]") || + net.ParseIP(host) != nil { + return false, fmt.Errorf("URI with IP (%q) cannot be matched against constraints", uri.String()) + } + + return matchDomainConstraint(host, constraint) +} + +func matchIPConstraint(ip net.IP, constraint *net.IPNet) (bool, error) { + if len(ip) != len(constraint.IP) { + return false, nil + } + + for i := range ip { + if mask := constraint.Mask[i]; ip[i]&mask != constraint.IP[i]&mask { + return false, nil + } + } + + return true, nil +} + +func matchDomainConstraint(domain, constraint string) (bool, error) { + // The meaning of zero length constraints is not specified, but this + // code follows NSS and accepts them as matching everything. + if len(constraint) == 0 { + return true, nil + } + + domainLabels, ok := domainToReverseLabels(domain) + if !ok { + return false, fmt.Errorf("x509: internal error: cannot parse domain %q", domain) + } + + // RFC 5280 says that a leading period in a domain name means that at + // least one label must be prepended, but only for URI and email + // constraints, not DNS constraints. The code also supports that + // behaviour for DNS constraints. + + mustHaveSubdomains := false + if constraint[0] == '.' { + mustHaveSubdomains = true + constraint = constraint[1:] + } + + constraintLabels, ok := domainToReverseLabels(constraint) + if !ok { + return false, fmt.Errorf("x509: internal error: cannot parse domain %q", constraint) + } + + if len(domainLabels) < len(constraintLabels) || + (mustHaveSubdomains && len(domainLabels) == len(constraintLabels)) { + return false, nil + } + + for i, constraintLabel := range constraintLabels { + if !strings.EqualFold(constraintLabel, domainLabels[i]) { + return false, nil + } + } + + return true, nil +} + +// checkNameConstraints checks that c permits a child certificate to claim the +// given name, of type nameType. The argument parsedName contains the parsed +// form of name, suitable for passing to the match function. The total number +// of comparisons is tracked in the given count and should not exceed the given +// limit. +func (c *Certificate) checkNameConstraints(count *int, + maxConstraintComparisons int, + nameType string, + name string, + parsedName any, + match func(parsedName, constraint any) (match bool, err error), + permitted, excluded any) error { + + excludedValue := reflect.ValueOf(excluded) + + *count += excludedValue.Len() + if *count > maxConstraintComparisons { + return CertificateInvalidError{c, TooManyConstraints, ""} + } + + for i := 0; i < excludedValue.Len(); i++ { + constraint := excludedValue.Index(i).Interface() + match, err := match(parsedName, constraint) + if err != nil { + return CertificateInvalidError{c, CANotAuthorizedForThisName, err.Error()} + } + + if match { + return CertificateInvalidError{c, CANotAuthorizedForThisName, fmt.Sprintf("%s %q is excluded by constraint %q", nameType, name, constraint)} + } + } + + permittedValue := reflect.ValueOf(permitted) + + *count += permittedValue.Len() + if *count > maxConstraintComparisons { + return CertificateInvalidError{c, TooManyConstraints, ""} + } + + ok := true + for i := 0; i < permittedValue.Len(); i++ { + constraint := permittedValue.Index(i).Interface() + + var err error + if ok, err = match(parsedName, constraint); err != nil { + return CertificateInvalidError{c, CANotAuthorizedForThisName, err.Error()} + } + + if ok { + break + } + } + + if !ok { + return CertificateInvalidError{c, CANotAuthorizedForThisName, fmt.Sprintf("%s %q is not permitted by any constraint", nameType, name)} + } + + return nil +} + +// isValid performs validity checks on c given that it is a candidate to append +// to the chain in currentChain. +func (c *Certificate) isValid(certType int, currentChain []*Certificate, opts *VerifyOptions) error { + if len(c.UnhandledCriticalExtensions) > 0 { + return UnhandledCriticalExtension{} + } + + if len(currentChain) > 0 { + child := currentChain[len(currentChain)-1] + if !bytes.Equal(child.RawIssuer, c.RawSubject) { + return CertificateInvalidError{c, NameMismatch, ""} + } + } + + now := opts.CurrentTime + if now.IsZero() { + now = time.Now() + } + if now.Before(c.NotBefore) { + return CertificateInvalidError{ + Cert: c, + Reason: Expired, + Detail: fmt.Sprintf("current time %s is before %s", now.Format(time.RFC3339), c.NotBefore.Format(time.RFC3339)), + } + } else if now.After(c.NotAfter) { + return CertificateInvalidError{ + Cert: c, + Reason: Expired, + Detail: fmt.Sprintf("current time %s is after %s", now.Format(time.RFC3339), c.NotAfter.Format(time.RFC3339)), + } + } + + maxConstraintComparisons := opts.MaxConstraintComparisions + if maxConstraintComparisons == 0 { + maxConstraintComparisons = 250000 + } + comparisonCount := 0 + + if certType == intermediateCertificate || certType == rootCertificate { + if len(currentChain) == 0 { + return errors.New("x509: internal error: empty chain when appending CA cert") + } + } + + if (certType == intermediateCertificate || certType == rootCertificate) && + c.hasNameConstraints() { + toCheck := []*Certificate{} + for _, c := range currentChain { + if c.hasSANExtension() { + toCheck = append(toCheck, c) + } + } + for _, sanCert := range toCheck { + err := forEachSAN(sanCert.getSANExtension(), func(tag int, data []byte) error { + switch tag { + case nameTypeEmail: + name := string(data) + mailbox, ok := parseRFC2821Mailbox(name) + if !ok { + return fmt.Errorf("x509: cannot parse rfc822Name %q", mailbox) + } + + if err := c.checkNameConstraints(&comparisonCount, maxConstraintComparisons, "email address", name, mailbox, + func(parsedName, constraint any) (bool, error) { + return matchEmailConstraint(parsedName.(rfc2821Mailbox), constraint.(string)) + }, c.PermittedEmailAddresses, c.ExcludedEmailAddresses); err != nil { + return err + } + + case nameTypeDNS: + name := string(data) + if _, ok := domainToReverseLabels(name); !ok { + return fmt.Errorf("x509: cannot parse dnsName %q", name) + } + + if err := c.checkNameConstraints(&comparisonCount, maxConstraintComparisons, "DNS name", name, name, + func(parsedName, constraint any) (bool, error) { + return matchDomainConstraint(parsedName.(string), constraint.(string)) + }, c.PermittedDNSDomains, c.ExcludedDNSDomains); err != nil { + return err + } + + case nameTypeURI: + name := string(data) + uri, err := url.Parse(name) + if err != nil { + return fmt.Errorf("x509: internal error: URI SAN %q failed to parse", name) + } + + if err := c.checkNameConstraints(&comparisonCount, maxConstraintComparisons, "URI", name, uri, + func(parsedName, constraint any) (bool, error) { + return matchURIConstraint(parsedName.(*url.URL), constraint.(string)) + }, c.PermittedURIDomains, c.ExcludedURIDomains); err != nil { + return err + } + + case nameTypeIP: + ip := net.IP(data) + if l := len(ip); l != net.IPv4len && l != net.IPv6len { + return fmt.Errorf("x509: internal error: IP SAN %x failed to parse", data) + } + + if err := c.checkNameConstraints(&comparisonCount, maxConstraintComparisons, "IP address", ip.String(), ip, + func(parsedName, constraint any) (bool, error) { + return matchIPConstraint(parsedName.(net.IP), constraint.(*net.IPNet)) + }, c.PermittedIPRanges, c.ExcludedIPRanges); err != nil { + return err + } + + default: + // Unknown SAN types are ignored. + } + + return nil + }) + + if err != nil { + return err + } + } + } + + // KeyUsage status flags are ignored. From Engineering Security, Peter + // Gutmann: A European government CA marked its signing certificates as + // being valid for encryption only, but no-one noticed. Another + // European CA marked its signature keys as not being valid for + // signatures. A different CA marked its own trusted root certificate + // as being invalid for certificate signing. Another national CA + // distributed a certificate to be used to encrypt data for the + // country’s tax authority that was marked as only being usable for + // digital signatures but not for encryption. Yet another CA reversed + // the order of the bit flags in the keyUsage due to confusion over + // encoding endianness, essentially setting a random keyUsage in + // certificates that it issued. Another CA created a self-invalidating + // certificate by adding a certificate policy statement stipulating + // that the certificate had to be used strictly as specified in the + // keyUsage, and a keyUsage containing a flag indicating that the RSA + // encryption key could only be used for Diffie-Hellman key agreement. + + if certType == intermediateCertificate && (!c.BasicConstraintsValid || !c.IsCA) { + return CertificateInvalidError{c, NotAuthorizedToSign, ""} + } + + if c.BasicConstraintsValid && c.MaxPathLen >= 0 { + numIntermediates := len(currentChain) - 1 + if numIntermediates > c.MaxPathLen { + return CertificateInvalidError{c, TooManyIntermediates, ""} + } + } + + if !boringAllowCert(c) { + // IncompatibleUsage is not quite right here, + // but it's also the "no chains found" error + // and is close enough. + return CertificateInvalidError{c, IncompatibleUsage, ""} + } + + return nil +} + +// Verify attempts to verify c by building one or more chains from c to a +// certificate in opts.Roots, using certificates in opts.Intermediates if +// needed. If successful, it returns one or more chains where the first +// element of the chain is c and the last element is from opts.Roots. +// +// If opts.Roots is nil, the platform verifier might be used, and +// verification details might differ from what is described below. If system +// roots are unavailable the returned error will be of type SystemRootsError. +// +// Name constraints in the intermediates will be applied to all names claimed +// in the chain, not just opts.DNSName. Thus it is invalid for a leaf to claim +// example.com if an intermediate doesn't permit it, even if example.com is not +// the name being validated. Note that DirectoryName constraints are not +// supported. +// +// Name constraint validation follows the rules from RFC 5280, with the +// addition that DNS name constraints may use the leading period format +// defined for emails and URIs. When a constraint has a leading period +// it indicates that at least one additional label must be prepended to +// the constrained name to be considered valid. +// +// Extended Key Usage values are enforced nested down a chain, so an intermediate +// or root that enumerates EKUs prevents a leaf from asserting an EKU not in that +// list. (While this is not specified, it is common practice in order to limit +// the types of certificates a CA can issue.) +// +// Certificates that use SHA1WithRSA and ECDSAWithSHA1 signatures are not supported, +// and will not be used to build chains. +// +// Certificates other than c in the returned chains should not be modified. +// +// WARNING: this function doesn't do any revocation checking. +func (c *Certificate) Verify(opts VerifyOptions) (chains [][]*Certificate, err error) { + // Platform-specific verification needs the ASN.1 contents so + // this makes the behavior consistent across platforms. + if len(c.Raw) == 0 { + return nil, errNotParsed + } + for i := 0; i < opts.Intermediates.len(); i++ { + c, err := opts.Intermediates.cert(i) + if err != nil { + return nil, fmt.Errorf("crypto/x509: error fetching intermediate: %w", err) + } + if len(c.Raw) == 0 { + return nil, errNotParsed + } + } + + // Use platform verifiers, where available, if Roots is from SystemCertPool. + if runtime.GOOS == "windows" || runtime.GOOS == "darwin" || runtime.GOOS == "ios" { + // Don't use the system verifier if the system pool was replaced with a non-system pool, + // i.e. if SetFallbackRoots was called with x509usefallbackroots=1. + systemPool := systemRootsPool() + if opts.Roots == nil && (systemPool == nil || systemPool.systemPool) { + return c.systemVerify(&opts) + } + if opts.Roots != nil && opts.Roots.systemPool { + platformChains, err := c.systemVerify(&opts) + // If the platform verifier succeeded, or there are no additional + // roots, return the platform verifier result. Otherwise, continue + // with the Go verifier. + if err == nil || opts.Roots.len() == 0 { + return platformChains, err + } + } + } + + if opts.Roots == nil { + opts.Roots = systemRootsPool() + if opts.Roots == nil { + return nil, SystemRootsError{systemRootsErr} + } + } + + err = c.isValid(leafCertificate, nil, &opts) + if err != nil { + return + } + + if len(opts.DNSName) > 0 { + err = c.VerifyHostname(opts.DNSName) + if err != nil { + return + } + } + + var candidateChains [][]*Certificate + if opts.Roots.contains(c) { + candidateChains = [][]*Certificate{{c}} + } else { + candidateChains, err = c.buildChains([]*Certificate{c}, nil, &opts) + if err != nil { + return nil, err + } + } + + if len(opts.KeyUsages) == 0 { + opts.KeyUsages = []ExtKeyUsage{ExtKeyUsageServerAuth} + } + + for _, eku := range opts.KeyUsages { + if eku == ExtKeyUsageAny { + // If any key usage is acceptable, no need to check the chain for + // key usages. + return candidateChains, nil + } + } + + chains = make([][]*Certificate, 0, len(candidateChains)) + for _, candidate := range candidateChains { + if checkChainForKeyUsage(candidate, opts.KeyUsages) { + chains = append(chains, candidate) + } + } + + if len(chains) == 0 { + return nil, CertificateInvalidError{c, IncompatibleUsage, ""} + } + + return chains, nil +} + +func appendToFreshChain(chain []*Certificate, cert *Certificate) []*Certificate { + n := make([]*Certificate, len(chain)+1) + copy(n, chain) + n[len(chain)] = cert + return n +} + +// alreadyInChain checks whether a candidate certificate is present in a chain. +// Rather than doing a direct byte for byte equivalency check, we check if the +// subject, public key, and SAN, if present, are equal. This prevents loops that +// are created by mutual cross-signatures, or other cross-signature bridge +// oddities. +func alreadyInChain(candidate *Certificate, chain []*Certificate) bool { + type pubKeyEqual interface { + Equal(crypto.PublicKey) bool + } + + var candidateSAN *pkix.Extension + for _, ext := range candidate.Extensions { + if ext.Id.Equal(oidExtensionSubjectAltName) { + candidateSAN = &ext + break + } + } + + for _, cert := range chain { + if !bytes.Equal(candidate.RawSubject, cert.RawSubject) { + continue + } + if !candidate.PublicKey.(pubKeyEqual).Equal(cert.PublicKey) { + continue + } + var certSAN *pkix.Extension + for _, ext := range cert.Extensions { + if ext.Id.Equal(oidExtensionSubjectAltName) { + certSAN = &ext + break + } + } + if candidateSAN == nil && certSAN == nil { + return true + } else if candidateSAN == nil || certSAN == nil { + return false + } + if bytes.Equal(candidateSAN.Value, certSAN.Value) { + return true + } + } + return false +} + +// maxChainSignatureChecks is the maximum number of CheckSignatureFrom calls +// that an invocation of buildChains will (transitively) make. Most chains are +// less than 15 certificates long, so this leaves space for multiple chains and +// for failed checks due to different intermediates having the same Subject. +const maxChainSignatureChecks = 100 + +func (c *Certificate) buildChains(currentChain []*Certificate, sigChecks *int, opts *VerifyOptions) (chains [][]*Certificate, err error) { + var ( + hintErr error + hintCert *Certificate + ) + + considerCandidate := func(certType int, candidate *Certificate) { + if candidate.PublicKey == nil || alreadyInChain(candidate, currentChain) { + return + } + + if sigChecks == nil { + sigChecks = new(int) + } + *sigChecks++ + if *sigChecks > maxChainSignatureChecks { + err = errors.New("x509: signature check attempts limit reached while verifying certificate chain") + return + } + + if err := c.CheckSignatureFrom(candidate); err != nil { + if hintErr == nil { + hintErr = err + hintCert = candidate + } + return + } + + err = candidate.isValid(certType, currentChain, opts) + if err != nil { + if hintErr == nil { + hintErr = err + hintCert = candidate + } + return + } + + switch certType { + case rootCertificate: + chains = append(chains, appendToFreshChain(currentChain, candidate)) + case intermediateCertificate: + var childChains [][]*Certificate + childChains, err = candidate.buildChains(appendToFreshChain(currentChain, candidate), sigChecks, opts) + chains = append(chains, childChains...) + } + } + + for _, root := range opts.Roots.findPotentialParents(c) { + considerCandidate(rootCertificate, root) + } + for _, intermediate := range opts.Intermediates.findPotentialParents(c) { + considerCandidate(intermediateCertificate, intermediate) + } + + if len(chains) > 0 { + err = nil + } + if len(chains) == 0 && err == nil { + err = UnknownAuthorityError{c, hintErr, hintCert} + } + + return +} + +func validHostnamePattern(host string) bool { return validHostname(host, true) } +func validHostnameInput(host string) bool { return validHostname(host, false) } + +// validHostname reports whether host is a valid hostname that can be matched or +// matched against according to RFC 6125 2.2, with some leniency to accommodate +// legacy values. +func validHostname(host string, isPattern bool) bool { + if !isPattern { + host = strings.TrimSuffix(host, ".") + } + if len(host) == 0 { + return false + } + + for i, part := range strings.Split(host, ".") { + if part == "" { + // Empty label. + return false + } + if isPattern && i == 0 && part == "*" { + // Only allow full left-most wildcards, as those are the only ones + // we match, and matching literal '*' characters is probably never + // the expected behavior. + continue + } + for j, c := range part { + if 'a' <= c && c <= 'z' { + continue + } + if '0' <= c && c <= '9' { + continue + } + if 'A' <= c && c <= 'Z' { + continue + } + if c == '-' && j != 0 { + continue + } + if c == '_' { + // Not a valid character in hostnames, but commonly + // found in deployments outside the WebPKI. + continue + } + return false + } + } + + return true +} + +func matchExactly(hostA, hostB string) bool { + if hostA == "" || hostA == "." || hostB == "" || hostB == "." { + return false + } + return toLowerCaseASCII(hostA) == toLowerCaseASCII(hostB) +} + +func matchHostnames(pattern, host string) bool { + pattern = toLowerCaseASCII(pattern) + host = toLowerCaseASCII(strings.TrimSuffix(host, ".")) + + if len(pattern) == 0 || len(host) == 0 { + return false + } + + patternParts := strings.Split(pattern, ".") + hostParts := strings.Split(host, ".") + + if len(patternParts) != len(hostParts) { + return false + } + + for i, patternPart := range patternParts { + if i == 0 && patternPart == "*" { + continue + } + if patternPart != hostParts[i] { + return false + } + } + + return true +} + +// toLowerCaseASCII returns a lower-case version of in. See RFC 6125 6.4.1. We use +// an explicitly ASCII function to avoid any sharp corners resulting from +// performing Unicode operations on DNS labels. +func toLowerCaseASCII(in string) string { + // If the string is already lower-case then there's nothing to do. + isAlreadyLowerCase := true + for _, c := range in { + if c == utf8.RuneError { + // If we get a UTF-8 error then there might be + // upper-case ASCII bytes in the invalid sequence. + isAlreadyLowerCase = false + break + } + if 'A' <= c && c <= 'Z' { + isAlreadyLowerCase = false + break + } + } + + if isAlreadyLowerCase { + return in + } + + out := []byte(in) + for i, c := range out { + if 'A' <= c && c <= 'Z' { + out[i] += 'a' - 'A' + } + } + return string(out) +} + +// VerifyHostname returns nil if c is a valid certificate for the named host. +// Otherwise it returns an error describing the mismatch. +// +// IP addresses can be optionally enclosed in square brackets and are checked +// against the IPAddresses field. Other names are checked case insensitively +// against the DNSNames field. If the names are valid hostnames, the certificate +// fields can have a wildcard as the complete left-most label (e.g. *.example.com). +// +// Note that the legacy Common Name field is ignored. +func (c *Certificate) VerifyHostname(h string) error { + // IP addresses may be written in [ ]. + candidateIP := h + if len(h) >= 3 && h[0] == '[' && h[len(h)-1] == ']' { + candidateIP = h[1 : len(h)-1] + } + if ip := net.ParseIP(candidateIP); ip != nil { + // We only match IP addresses against IP SANs. + // See RFC 6125, Appendix B.2. + for _, candidate := range c.IPAddresses { + if ip.Equal(candidate) { + return nil + } + } + return HostnameError{c, candidateIP} + } + + candidateName := toLowerCaseASCII(h) // Save allocations inside the loop. + validCandidateName := validHostnameInput(candidateName) + + for _, match := range c.DNSNames { + // Ideally, we'd only match valid hostnames according to RFC 6125 like + // browsers (more or less) do, but in practice Go is used in a wider + // array of contexts and can't even assume DNS resolution. Instead, + // always allow perfect matches, and only apply wildcard and trailing + // dot processing to valid hostnames. + if validCandidateName && validHostnamePattern(match) { + if matchHostnames(match, candidateName) { + return nil + } + } else { + if matchExactly(match, candidateName) { + return nil + } + } + } + + return HostnameError{c, h} +} + +func checkChainForKeyUsage(chain []*Certificate, keyUsages []ExtKeyUsage) bool { + usages := make([]ExtKeyUsage, len(keyUsages)) + copy(usages, keyUsages) + + if len(chain) == 0 { + return false + } + + usagesRemaining := len(usages) + + // We walk down the list and cross out any usages that aren't supported + // by each certificate. If we cross out all the usages, then the chain + // is unacceptable. + +NextCert: + for i := len(chain) - 1; i >= 0; i-- { + cert := chain[i] + if len(cert.ExtKeyUsage) == 0 && len(cert.UnknownExtKeyUsage) == 0 { + // The certificate doesn't have any extended key usage specified. + continue + } + + for _, usage := range cert.ExtKeyUsage { + if usage == ExtKeyUsageAny { + // The certificate is explicitly good for any usage. + continue NextCert + } + } + + const invalidUsage ExtKeyUsage = -1 + + NextRequestedUsage: + for i, requestedUsage := range usages { + if requestedUsage == invalidUsage { + continue + } + + for _, usage := range cert.ExtKeyUsage { + if requestedUsage == usage { + continue NextRequestedUsage + } + } + + usages[i] = invalidUsage + usagesRemaining-- + if usagesRemaining == 0 { + return false + } + } + } + + return true +} |