1 files changed, 219 insertions, 0 deletions

diff --git a/tls/ocsp.go b/tls/ocsp.go
new file mode 100644
index 0000000..94f7f68
--- /dev/null
+++ b/tls/ocsp.go
@@ -0,0 +1,219 @@
+package tls
+
+import (
+        "bytes"
+        "context"
+        "crypto/tls"
+        "crypto/x509"
+        "errors"
+        "fmt"
+        "io"
+        "net/http"
+        "sync"
+        "time"
+
+        "golang.org/x/crypto/ocsp"
+)
+
+type OcspError struct {
+        Err    error
+        AtBoot bool
+}
+
+func (e OcspError) Error() string {
+        return e.Err.Error()
+}
+
+func (e OcspError) Unwrap() error {
+        return e.Err
+}
+
+type OcspLogger interface {
+        Info(...interface{})
+        Errorf(string, ...interface{})
+}
+
+func OcspErrorLogger(l OcspLogger, c <-chan OcspError) func(context.Context, *sync.WaitGroup) error {
+        return func(ctx context.Context, wg *sync.WaitGroup) error {
+                wg.Add(1)
+                defer wg.Done()
+
+                for {
+                        select {
+                        case err := <-c:
+                                l.Errorf("Error in OCSP stapling: %w", errors.Unwrap(err))
+                        case <-ctx.Done():
+                                l.Info("Shutting down OCSP logger")
+                                return nil
+                        }
+                }
+        }
+}
+
+type OcspManager struct {
+        CertPath, KeyPath string
+        Errors            chan<- OcspError
+        cert              *tls.Certificate
+        ocspRes           *ocsp.Response
+        sync.RWMutex
+}
+
+func (m *OcspManager) loadCert() error {
+        cert, err := tls.LoadX509KeyPair(m.CertPath, m.KeyPath)
+        if err != nil {
+                return err
+        }
+        m.Lock()
+        m.cert = &cert
+        m.Unlock()
+
+        return nil
+}
+
+func (m *OcspManager) stapleCert() error {
+        // This makes a network request to an unknown server so don't hold the full
+        // lock while this is happening
+        m.RLock()
+        raw, ocspRes, err := GetOcspResponse(m.cert)
+        if err != nil {
+                return err
+        }
+        m.RUnlock()
+
+        m.Lock()
+        m.cert.OCSPStaple = raw
+        m.ocspRes = ocspRes
+        m.Unlock()
+
+        return nil
+}
+
+func (m *OcspManager) Init() error {
+        // All functions called here will handle locking themselves
+        if err := m.loadCert(); err != nil {
+                return err
+        }
+
+        if err := m.stapleCert(); err != nil {
+                return err
+        }
+
+        return nil
+}
+
+func (m *OcspManager) Run(ctx context.Context, wg *sync.WaitGroup) error {
+        wg.Add(1)
+        defer wg.Done()
+
+        t := time.NewTimer(m.ocspRes.NextUpdate.Sub(time.Now()) - time.Hour)
+
+        for {
+                select {
+                case <-t.C:
+                        if err := m.stapleCert(); err != nil {
+                                if m.Errors != nil {
+                                        m.Errors <- OcspError{err, false}
+                                }
+                                t.Reset(time.Hour)
+                                continue
+                        }
+                        // We own this object and only we write it, no need to lock
+                        t.Reset(m.ocspRes.NextUpdate.Sub(time.Now()) - time.Hour)
+                case <-ctx.Done():
+                        return nil
+                }
+        }
+}
+
+func (m *OcspManager) GetCertificate(h *tls.ClientHelloInfo) (*tls.Certificate, error) {
+        m.RLock()
+        defer m.RUnlock()
+
+        if m.cert != nil {
+                return m.cert, nil
+        }
+
+        return nil, fmt.Errorf("OCSP manager has no certificate stored")
+}
+
+func GetOcspResponse(chain *tls.Certificate) ([]byte, *ocsp.Response, error) {
+        var certs []*x509.Certificate
+        for _, c := range chain.Certificate {
+                cert, err := x509.ParseCertificate(c)
+                if err != nil {
+                        return nil, nil, err
+                }
+                certs = append(certs, cert)
+        }
+        if len(certs) == 0 {
+                return nil, nil, fmt.Errorf("no certificates found in bundle")
+        }
+
+        // We expect the certificate slice to be ordered downwards the chain.
+        // SRV CRT -> CA. We need to pull the leaf and issuer certs out of it,
+        // which should always be the first two certificates. If there's no
+        // OCSP server listed in the leaf cert, there's nothing to do. And if
+        // we have only one certificate so far, we need to get the issuer cert.
+        leaf := certs[0]
+        if len(leaf.OCSPServer) == 0 {
+                return nil, nil, fmt.Errorf("no OCSP server specified in certificate")
+        }
+
+        if len(certs) == 1 {
+                if len(leaf.IssuingCertificateURL) == 0 {
+                        return nil, nil, fmt.Errorf("no URL to issuing certificate")
+                }
+
+                resp, err := http.Get(leaf.IssuingCertificateURL[0])
+                if err != nil {
+                        return nil, nil, fmt.Errorf("getting issuer certificate: %w", err)
+                }
+                defer resp.Body.Close()
+
+                issuerBytes, err := io.ReadAll(io.LimitReader(resp.Body, 1024*1024))
+                if err != nil {
+                        return nil, nil, fmt.Errorf("reading issuer certificate: %w", err)
+                }
+
+                issuer, err := x509.ParseCertificate(issuerBytes)
+                if err != nil {
+                        return nil, nil, fmt.Errorf("parsing issuer certificate: %w", err)
+                }
+
+                certs = append(certs, issuer)
+        }
+
+        issuer := certs[1]
+
+        req, err := ocsp.CreateRequest(leaf, issuer, nil)
+        if err != nil {
+                return nil, nil, fmt.Errorf("creating OCSP request: %w", err)
+        }
+
+        httpRes, err := http.Post(leaf.OCSPServer[0], "application/ocsp-request", bytes.NewReader(req))
+        if err != nil {
+                return nil, nil, fmt.Errorf("making OCSP request: %w", err)
+        }
+        defer httpRes.Body.Close()
+
+        rawRes, err := io.ReadAll(io.LimitReader(httpRes.Body, 1024*1024))
+        if err != nil {
+                return nil, nil, fmt.Errorf("reading OCSP response: %w", err)
+        }
+
+        res, err := ocsp.ParseResponse(rawRes, issuer)
+        if err != nil {
+                return nil, nil, fmt.Errorf("parsing OCSP response: %w", err)
+        }
+
+        if res.Status != ocsp.Good {
+                return nil, nil, fmt.Errorf("invalid: OCSP response was not of Good status")
+        }
+
+        // This is invalid, the response expires after the certificate
+        if res.NextUpdate.After(leaf.NotAfter) {
+                return nil, nil, fmt.Errorf("invalid: OCSP response valid after certificate expiration")
+        }
+
+        return rawRes, res, nil
+}