OF-405 : Perform proper path validation on certificate chains

What this patch actually does is place existing certificates into a CertStore,
including those from its (untrusted) keystore, the trust store, and any from
the chain supplied by the peer, and then rebuild a chain back to a known trust
anchor (from the trust store).

This strategy will cope with unknown ICAs in chains, abbreviated chains, and so
on, and replaces attempts to specifically handle self-signed certificates.

That last said, there is an explicit shortcut to handle self-signed certificates
which are supplied as end-entity certificates. These are simply checked against
the trust store without any attempt to build a path.

src/java/org/jivesoftware/openfire/net/SASLAuthentication.java

@@ -187,24 +187,18 @@ public class SASLAuthentication {
         if (session instanceof IncomingServerSession) {
             // Server connections don't follow the same rules as clients
             if (session.isSecure()) {
-                boolean usingSelfSigned;
-                final Certificate[] chain = session.getConnection().getLocalCertificates();
-                if (chain == null || chain.length == 0) {
-                	usingSelfSigned = true;
-                } else {
+                boolean usingSelfSigned = true;
+
                 try {
-						usingSelfSigned = CertificateManager.isSelfSignedCertificate(SSLConfig.getKeyStore(), (X509Certificate) chain[0]);
-					} catch (KeyStoreException ex) {
-						Log.warn("Exception occurred while trying to determine whether local certificate is self-signed. Proceeding as if it is.", ex);
-						usingSelfSigned = true;
+                    X509Certificate trusted = CertificateManager.getEndEntityCertificate(session.getConnection().getPeerCertificates(), SSLConfig.getKeyStore(), SSLConfig.gets2sTrustStore());
+                    usingSelfSigned = trusted == null;
                 } catch (IOException ex) {
-						Log.warn("Exception occurred while trying to determine whether local certificate is self-signed. Proceeding as if it is.", ex);
+                    Log.warn("Exception occurred while trying to determine whether remote certificate is trusted. Proceeding as if it is.", ex);
                     usingSelfSigned = true;
                 }
-                }
                 
                 if (!usingSelfSigned) {
-                    // Offer SASL EXTERNAL only if TLS has already been negotiated and we are not
+                    // Offer SASL EXTERNAL only if TLS has already been negotiated and the peer is not
                     // using a self-signed certificate
                     sb.append("<mechanism>EXTERNAL</mechanism>");
                 }
@@ -229,13 +223,23 @@ public class SASLAuthentication {
         Element mechs = DocumentHelper.createElement(new QName("mechanisms",
                 new Namespace("", "urn:ietf:params:xml:ns:xmpp-sasl")));
         if (session instanceof IncomingServerSession) {
-            // Server connections dont follow the same rules as clients
+            // Server connections don't follow the same rules as clients
             if (session.isSecure()) {
-                // Offer SASL EXTERNAL only if TLS has already been negotiated
+                boolean usingSelfSigned = true;
+                try {
+                    X509Certificate trusted = CertificateManager.getEndEntityCertificate(((LocalSession)session).getConnection().getPeerCertificates(), SSLConfig.getKeyStore(), SSLConfig.gets2sTrustStore());
+                    usingSelfSigned = trusted == null;
+                } catch (IOException ex) {
+                    Log.warn("Exception occurred while trying to determine whether remote certificate is trusted. Proceeding as if it is.", ex);
+                    usingSelfSigned = true;
+                }
+                if (!usingSelfSigned) {
+                    // Offer SASL EXTERNAL only if TLS has already been negotiated and the peer has a trusted cert.
                     Element mechanism = mechs.addElement("mechanism");
                     mechanism.setText("EXTERNAL");
                 }
             }
+        }
         else {
             for (String mech : getSupportedMechanisms()) {
                 Element mechanism = mechs.addElement("mechanism");
@@ -546,7 +550,7 @@ public class SASLAuthentication {
             }
     
             hostname = new String(StringUtils.decodeBase64(hostname), CHARSET);
-            // Check if cerificate validation is disabled for s2s
+            // Check if certificate validation is disabled for s2s
             // Flag that indicates if certificates of the remote server should be validated.
             // Disabling certificate validation is not recommended for production environments.
             boolean verify =
@@ -557,9 +561,11 @@ public class SASLAuthentication {
             }
             // Check that hostname matches the one provided in a certificate
             Connection connection = session.getConnection();
+            try {
+                X509Certificate trusted = CertificateManager.getEndEntityCertificate(connection.getPeerCertificates(), SSLConfig.getKeyStore(), SSLConfig.gets2sTrustStore());
 
-            for (Certificate certificate : connection.getPeerCertificates()) {
-                for (String identity : CertificateManager.getPeerIdentities((X509Certificate) certificate)) {
+                if (trusted != null) {
+                    for (String identity : CertificateManager.getPeerIdentities(trusted)) {
                         // Verify that either the identity is the same as the hostname, or for wildcarded
                         // identities that the hostname ends with .domainspecified or -is- domainspecified.
                         if ((identity.startsWith("*.")
@@ -571,6 +577,9 @@ public class SASLAuthentication {
                         }
                     }
                 }
+            } catch(IOException e) {
+                /// Keystore problem.
+            }
 
         }
         else if (session instanceof LocalClientSession) {

src/java/org/jivesoftware/util/CertificateManager.java

@@ -37,9 +37,19 @@ import java.security.Provider;
 import java.security.PublicKey;
 import java.security.SecureRandom;
 import java.security.Security;
+import java.security.cert.CertPath;
+import java.security.cert.CertPathBuilder;
+import java.security.cert.CertPathBuilderException;
+import java.security.cert.CertPathValidator;
+import java.security.cert.CertPathValidatorException;
+import java.security.cert.CertStore;
 import java.security.cert.Certificate;
 import java.security.cert.CertificateFactory;
 import java.security.cert.CertificateParsingException;
+import java.security.cert.CollectionCertStoreParameters;
+import java.security.cert.PKIXBuilderParameters;
+import java.security.cert.TrustAnchor;
+import java.security.cert.X509CertSelector;
 import java.security.cert.X509Certificate;
 import java.util.ArrayList;
 import java.util.Collection;
@@ -47,6 +57,7 @@ import java.util.Collections;
 import java.util.Date;
 import java.util.Enumeration;
 import java.util.HashMap;
+import java.util.HashSet;
 import java.util.Hashtable;
 import java.util.LinkedList;
 import java.util.List;
@@ -208,6 +219,110 @@ public class CertificateManager {
         }
     }
 
+    /**
+     * Decide whether or not to trust the given supplied certificate chain, returning the
+     * End Entity Certificate in this case where it can, and null otherwise.
+     * A self-signed certificate will, for example, return null.
+     * For certain failures, we SHOULD generate an exception - revocations and the like.
+     *
+     * @param certChain an array of X509Certificate where the first one is the endEntityCertificate.
+     * @return a boolean indicating whether the endEntityCertificate should be trusted.
+     */
+    public static X509Certificate getEndEntityCertificate(Certificate chain[],
+            KeyStore certStore, KeyStore trustStore) {
+        if (chain.length == 0) {
+            return null;
+        }
+        X509Certificate first = (X509Certificate) chain[0];
+        if (chain.length == 1
+                && first.getSubjectDN().equals(first.getIssuerDN())) {
+            // Chain is single cert, and self-signed.
+            try {
+                if (trustStore.getCertificateAlias(first) != null) {
+                    // Interesting case: trusted self-signed cert.
+                    return first;
+                }
+            } catch (KeyStoreException e) {
+                // Ignore.
+            }
+            return null;
+        }
+        ArrayList<Object> all_certs = new ArrayList<Object>();
+        try {
+            // First, load up certStore contents into a CertStore.
+            // It's a mystery why these objects are different.
+            for (Enumeration<String> aliases = certStore.aliases(); aliases
+                    .hasMoreElements();) {
+                String alias = aliases.nextElement();
+                if (certStore.isCertificateEntry(alias)) {
+                    X509Certificate cert = (X509Certificate) certStore
+                            .getCertificate(alias);
+                    all_certs.add(cert);
+                }
+            }
+            // Now add the trusted certs.
+            for (Enumeration<String> aliases = trustStore.aliases(); aliases
+                    .hasMoreElements();) {
+                String alias = aliases.nextElement();
+                if (trustStore.isCertificateEntry(alias)) {
+                    X509Certificate cert = (X509Certificate) trustStore
+                            .getCertificate(alias);
+                    all_certs.add(cert);
+                }
+            }
+            // Finally, add all the certs in the chain except the first:
+            for (int i = 0; i < chain.length; ++i) {
+                all_certs.add(chain[i]);
+            }
+            CertStore cs = CertStore.getInstance("Collection",
+                    new CollectionCertStoreParameters(all_certs));
+            X509CertSelector selector = new X509CertSelector();
+            selector.setCertificate(first);
+            // / selector.setSubject(first.getSubjectX500Principal());
+            PKIXBuilderParameters params = new PKIXBuilderParameters(
+                    trustStore, selector);
+            params.addCertStore(cs);
+            params.setDate(new Date());
+            params.setRevocationEnabled(false);
+            /* Code here is the right way to do things. */
+            CertPathBuilder pathBuilder = CertPathBuilder
+                    .getInstance(CertPathBuilder.getDefaultType());
+            CertPath cp = pathBuilder.build(params).getCertPath();
+            /**
+             * This section is an alternative to using CertPathBuilder which is
+             * not as complete (or safe), but will emit much better errors. If
+             * things break, swap around the code.
+             *
+             **** COMMENTED OUT. ****
+            ArrayList<X509Certificate> ls = new ArrayList<X509Certificate>();
+            for (int i = 0; i < chain.length; ++i) {
+                ls.add((X509Certificate) chain[i]);
+            }
+            for (X509Certificate last = ls.get(ls.size() - 1); !last
+                    .getIssuerDN().equals(last.getSubjectDN()); last = ls
+                    .get(ls.size() - 1)) {
+                X509CertSelector sel = new X509CertSelector();
+                sel.setSubject(last.getIssuerX500Principal());
+                ls.add((X509Certificate) cs.getCertificates(sel).toArray()[0]);
+            }
+            CertPath cp = CertificateFactory.getInstance("X.509").generateCertPath(ls);
+             ****** END ALTERNATIVE. ****
+             */
+            // Not entirely sure if I need to do this with CertPathBuilder.
+            // Can't hurt.
+            CertPathValidator pathValidator = CertPathValidator
+                    .getInstance("PKIX");
+            pathValidator.validate(cp, params);
+            return (X509Certificate) cp.getCertificates().get(0);
+        } catch (CertPathBuilderException e) {
+            Log.warn("Path builder: " + e.getMessage());
+        } catch (CertPathValidatorException e) {
+            Log.warn("Path validator: " + e.getMessage());
+        } catch (Exception e) {
+        }
+        return null;
+    }
+
     /**
      * Returns the identities of the remote server as defined in the specified certificate. The
      * identities are defined in the subjectDN of the certificate and it can also be defined in