mod_ssl: Add SSLClientHelloVars directive which exposes various

ClientHello properties in new SSL_CLIENTHELLO_* variables.

* modules/ssl/ssl_engine_kernel.c (ssl_hook_Fixup_vars): Add
  SSL_CLIENTHELLO_* vars.
  (copy_clienthello_vars): New function.
  (ssl_callback_ClientHello): Call it when needed.

* modules/ssl/ssl_engine_vars.c (ssl_var_lookup_ssl_clienthello): New
  function.
  (ssl_var_lookup_ssl): Call it for SSL_CLIENTHELLO_*.

* modules/ssl/ssl_private.h (modssl_clienthello_vars): Add type.
  (SSLConnRec): Add clienthello_vars pointer.

* modules/ssl/ssl_engine_config.c, modules/ssl/mod_ssl.c: Add handling
  of new SSLClientHelloVars directive.

Submitted by: Charles Smutz <csmutz gmail.com>
Github: closes apache#483


git-svn-id: https://svn.apache.org/repos/asf/httpd/httpd/trunk@1921074 13f79535-47bb-0310-9956-ffa450edef68

Author: notroj

changes-entries/ssl-hello-vars.txt

@@ -0,0 +1,3 @@
+  *) mod_ssl: Add SSLClientHelloVars directive to expose various
+     ClientHello properties as SSL_CLIENTHELLO_* variables.
+     [Charles Smutz <csmutz gmail.com>]

docs/manual/mod/mod_ssl.xml

@@ -110,6 +110,14 @@ compatibility variables.</p>
 <tr><td><code>SSL_SRP_USERINFO</code></td>              <td>string</td>    <td>SRP user info</td></tr>
 <tr><td><code>SSL_TLS_SNI</code></td>                   <td>string</td>    <td>Contents of the SNI TLS extension (if supplied with ClientHello)</td></tr>
 <tr><td><code>SSL_HANDSHAKE_RTT</code></td>             <td>number</td>    <td>Round-trip time of TLS handshake in microseconds including endpoint processing (set to empty string if OpenSSL version prior to 3.2 or if round-trip time can not be determined)</td></tr>
+<tr><td><code>SSL_CLIENTHELLO_VERSION</code></td>       <td>string</td>    <td>Version field (legacy) from ClientHello as four hex encoded characters</td></tr>
+<tr><td><code>SSL_CLIENTHELLO_CIPHERS</code></td>       <td>string</td>    <td>Cipher Suites from ClientHello as four hex encoded characters per item</td></tr>
+<tr><td><code>SSL_CLIENTHELLO_EXTENSIONS</code></td>    <td>string</td>    <td>Extension IDs from ClientHello as four hex encoded characters per item</td></tr>
+<tr><td><code>SSL_CLIENTHELLO_GROUPS</code></td>        <td>string</td>    <td>Value of Supported Groups extension (10) from ClientHello as four hex encoded characters per item</td></tr>
+<tr><td><code>SSL_CLIENTHELLO_EC_FORMATS</code></td>    <td>string</td>    <td>Value of EC Point Formats extension (11) from ClientHello as two hex encoded characters per item</td></tr>
+<tr><td><code>SSL_CLIENTHELLO_SIG_ALGOS</code></td>     <td>string</td>    <td>Value of Signature Algorithms extension (13) from ClientHello as four hex encoded characters per item</td></tr>
+<tr><td><code>SSL_CLIENTHELLO_ALPN</code></td>          <td>string</td>    <td>Value of ALPN extension (16) from ClientHello as hex encoded string including leading string lengths</td></tr>
+<tr><td><code>SSL_CLIENTHELLO_VERSIONS</code></td>      <td>string</td>    <td>Value of Supported Versions extension (43) from ClientHello as four hex encoded characters per item</td></tr>
 </table>
 
 <p><em>x509</em> specifies a component of an X.509 DN; one of
@@ -142,6 +150,10 @@ suffix (if any). For example, <code>SSL_SERVER_S_DN_OU_RAW</code> or
 <p><code>SSL_CLIENT_V_REMAIN</code> is only available in version 2.1
 and later.</p>
 
+<p>The <code>SSL_CLIENTHELLO_*</code> variables require the directive 
+<directive module="mod_ssl">SSLClientHelloVars</directive> to be 
+enabled or they will not be populated.</p>
+ 
 <p>A number of additional environment variables can also be used
 in <directive>SSLRequire</directive> expressions, or in custom log
 formats:</p>
@@ -2858,6 +2870,26 @@ be protected with file permissions similar to those used for
 </usage>
 </directivesynopsis>
 
+<directivesynopsis>
+<name>SSLClientHelloVars</name>
+<description>Enable collection of ClientHello variables</description>
+<syntax>SSLClientHelloVars on|off</syntax>
+<default>SSLClientHelloVars off</default>
+<contextlist><context>server config</context>
+<context>virtual host</context></contextlist>
+<compatibility>Available in httpd 2.5.2 and later, requires OpenSSL 1.1.1 or later</compatibility>
+
+<usage>
+<p>This directive enables collection of ClientHello data during the handshake that is retained for 
+the length of the connection so it can be exposed as <code>SSL_CLIENTHELLLO_*</code> environment 
+variables for requests depending upon the <code>StdEnvVars</code> setting. The variables are 
+formatted as the hex-encoded raw buffers seen in the raw network protocol and as provided 
+by OpenSSL. GREASE (RFC 8701) values are filtered by OpenSSL when enumerating extension IDs, but 
+otherwise, are passed through unchanged for other variables. If this directive is not enabled or 
+if OpenSSL prior to version 1.1.1 is used, these variables will not have a value set.</p>
+</usage> 
+</directivesynopsis>
+ 
 <directivesynopsis>
 <name>SSLCompression</name>
 <description>Enable compression on the SSL level</description>

modules/ssl/mod_ssl.c

@@ -166,6 +166,9 @@ static const command_rec ssl_config_cmds[] = {
                 "('[+-][" SSL_PROTOCOLS "] ...' - see manual)")
     SSL_CMD_SRV(HonorCipherOrder, FLAG,
                 "Use the server's cipher ordering preference")
+    SSL_CMD_SRV(ClientHelloVars, FLAG,
+                "Enable SSL ClientHello variable collection "
+                "(`on', `off')")
     SSL_CMD_SRV(Compression, FLAG,
                 "Enable SSL level compression "
                 "(`on', `off')")

modules/ssl/ssl_engine_config.c

@@ -220,6 +220,7 @@ static SSLSrvConfigRec *ssl_config_server_new(apr_pool_t *p)
 #ifndef OPENSSL_NO_COMP
     sc->compression            = UNSET;
 #endif
+    sc->clienthello_vars       = UNSET;
     sc->session_tickets        = UNSET;
 
     modssl_ctx_init_server(sc, p);
@@ -347,6 +348,7 @@ void *ssl_config_server_merge(apr_pool_t *p, void *basev, void *addv)
     cfgMerge(enabled, SSL_ENABLED_UNSET);
     cfgMergeInt(session_cache_timeout);
     cfgMergeBool(cipher_server_pref);
+    cfgMergeBool(clienthello_vars);
 #ifdef HAVE_TLSEXT
     cfgMerge(strict_sni_vhost_check, SSL_ENABLED_UNSET);
 #endif
@@ -957,6 +959,13 @@ const char *ssl_cmd_SSLCompression(cmd_parms *cmd, void *dcfg, int flag)
     return NULL;
 }
 
+const char *ssl_cmd_SSLClientHelloVars(cmd_parms *cmd, void *dcfg, int flag)
+{
+    SSLSrvConfigRec *sc = mySrvConfig(cmd->server);
+    sc->clienthello_vars = flag ? TRUE : FALSE;
+    return NULL;
+}
+
 const char *ssl_cmd_SSLHonorCipherOrder(cmd_parms *cmd, void *dcfg, int flag)
 {
 #ifdef SSL_OP_CIPHER_SERVER_PREFERENCE

modules/ssl/ssl_engine_kernel.c

@@ -1547,6 +1547,14 @@ static const char *const ssl_hook_Fixup_vars[] = {
     "SSL_SRP_USERINFO",
 #endif
     "SSL_HANDSHAKE_RTT",
+    "SSL_CLIENTHELLO_VERSION",
+    "SSL_CLIENTHELLO_CIPHERS",
+    "SSL_CLIENTHELLO_EXTENSIONS",
+    "SSL_CLIENTHELLO_GROUPS",
+    "SSL_CLIENTHELLO_EC_FORMATS",
+    "SSL_CLIENTHELLO_SIG_ALGOS",
+    "SSL_CLIENTHELLO_ALPN",
+    "SSL_CLIENTHELLO_VERSIONS",
     NULL
 };
 
@@ -2465,6 +2473,53 @@ int ssl_callback_ServerNameIndication(SSL *ssl, int *al, modssl_ctx_t *mctx)
 }
 
 #if OPENSSL_VERSION_NUMBER >= 0x10101000L && !defined(LIBRESSL_VERSION_NUMBER)
+/*
+ * Copy data from clienthello for env vars use later
+ */
+static void copy_clienthello_vars(conn_rec *c, SSL *ssl)
+{
+    SSLConnRec *sslcon;
+    modssl_clienthello_vars *clienthello_vars;
+    const unsigned char *data;
+    int *ids;
+
+    sslcon = myConnConfig(c);
+
+    sslcon->clienthello_vars = apr_pcalloc(c->pool, sizeof(*clienthello_vars));
+    clienthello_vars = sslcon->clienthello_vars;
+
+    clienthello_vars->version = SSL_client_hello_get0_legacy_version(ssl);
+    clienthello_vars->ciphers_len = SSL_client_hello_get0_ciphers(ssl, &data);
+    if (clienthello_vars->ciphers_len > 0) {
+        clienthello_vars->ciphers_data = apr_pmemdup(c->pool, data, clienthello_vars->ciphers_len);
+    }
+    if (SSL_client_hello_get1_extensions_present(ssl, &ids, &clienthello_vars->extids_len) == 1) {
+        if (clienthello_vars->extids_len > 0)
+            clienthello_vars->extids_data = apr_pmemdup(c->pool, ids, clienthello_vars->extids_len * sizeof(int));
+        OPENSSL_free(ids);
+    }
+    if (SSL_client_hello_get0_ext(ssl, TLSEXT_TYPE_supported_groups, &data, &clienthello_vars->ecgroups_len) == 1) {
+        if (clienthello_vars->ecgroups_len > 0)
+            clienthello_vars->ecgroups_data = apr_pmemdup(c->pool, data, clienthello_vars->ecgroups_len);
+    }
+    if (SSL_client_hello_get0_ext(ssl, TLSEXT_TYPE_ec_point_formats, &data, &clienthello_vars->ecformats_len) == 1) {
+        if (clienthello_vars->ecformats_len > 0)
+            clienthello_vars->ecformats_data = apr_pmemdup(c->pool, data, clienthello_vars->ecformats_len);
+    }
+    if (SSL_client_hello_get0_ext(ssl, TLSEXT_TYPE_signature_algorithms, &data, &clienthello_vars->sigalgos_len) == 1) {
+        if (clienthello_vars->sigalgos_len > 0)
+            clienthello_vars->sigalgos_data = apr_pmemdup(c->pool, data, clienthello_vars->sigalgos_len);
+    }
+    if (SSL_client_hello_get0_ext(ssl, TLSEXT_TYPE_application_layer_protocol_negotiation, &data, &clienthello_vars->alpn_len) == 1) {
+        if (clienthello_vars->alpn_len > 0)
+            clienthello_vars->alpn_data = apr_pmemdup(c->pool, data, clienthello_vars->alpn_len);
+    }
+    if (SSL_client_hello_get0_ext(ssl, TLSEXT_TYPE_supported_versions, &data, &clienthello_vars->versions_len) == 1) {
+        if (clienthello_vars->versions_len > 0)
+            clienthello_vars->versions_data = apr_pmemdup(c->pool, data, clienthello_vars->versions_len);
+    }
+}
+
 /*
  * This callback function is called when the ClientHello is received.
  */
@@ -2520,6 +2575,10 @@ int ssl_callback_ClientHello(SSL *ssl, int *al, void *arg)
 
 give_up:
     init_vhost(c, ssl, servername);
+    
+    if (mySrvConfigFromConn(c)->clienthello_vars == TRUE)
+        copy_clienthello_vars(c, ssl);
+
     return SSL_CLIENT_HELLO_SUCCESS;
 }
 #endif /* OPENSSL_VERSION_NUMBER < 0x10101000L */

modules/ssl/ssl_engine_vars.c

@@ -52,6 +52,7 @@ static const char *ssl_var_lookup_ssl_cert_verify(apr_pool_t *p, const SSLConnRe
 static const char *ssl_var_lookup_ssl_cipher(apr_pool_t *p, const SSLConnRec *sslconn, const char *var);
 static void  ssl_var_lookup_ssl_cipher_bits(SSL *ssl, int *usekeysize, int *algkeysize);
 static const char *ssl_var_lookup_ssl_handshake_rtt(apr_pool_t *p, SSL *ssl);
+static const char *ssl_var_lookup_ssl_clienthello(apr_pool_t *p, const SSLConnRec *sslconn, const char *var);
 static const char *ssl_var_lookup_ssl_version(const char *var);
 static const char *ssl_var_lookup_ssl_compress_meth(SSL *ssl);
 
@@ -476,6 +477,9 @@ static const char *ssl_var_lookup_ssl(apr_pool_t *p, const SSLConnRec *sslconn,
     else if (ssl != NULL && strcEQ(var, "HANDSHAKE_RTT")) {
         result = ssl_var_lookup_ssl_handshake_rtt(p, ssl);
     }
+    else if (ssl != NULL && strlen(var) >= 12 && strcEQn(var, "CLIENTHELLO_", 12)) {
+        result = ssl_var_lookup_ssl_clienthello(p, sslconn, var+12);
+    }
     else if (ssl != NULL && strlen(var) > 18 && strcEQn(var, "CLIENT_CERT_CHAIN_", 18)) {
         sk = SSL_get_peer_cert_chain(ssl);
         result = ssl_var_lookup_ssl_cert_chain(p, sk, var+18, 1);
@@ -975,6 +979,62 @@ static const char *ssl_var_lookup_ssl_handshake_rtt(apr_pool_t *p, SSL *ssl)
     return NULL;
 }
 
+static const char *ssl_var_lookup_ssl_clienthello(apr_pool_t *p, const SSLConnRec *sslconn, const char *var)
+{
+#if OPENSSL_VERSION_NUMBER >= 0x10101000L && !defined(LIBRESSL_VERSION_NUMBER)
+    char *value;
+    modssl_clienthello_vars *clienthello_vars;
+    apr_size_t i;
+
+    clienthello_vars = sslconn->clienthello_vars;
+
+    if (!clienthello_vars)
+        return NULL;
+
+    if (strEQ(var, "VERSION")) {
+        return apr_psprintf(p, "%04x", (uint16_t) clienthello_vars->version);
+    }
+    else if (strEQ(var, "CIPHERS") && (clienthello_vars->ciphers_len > 0)) {
+        value = apr_palloc(p, clienthello_vars->ciphers_len * 2 + 1);
+        ap_bin2hex(clienthello_vars->ciphers_data, clienthello_vars->ciphers_len, value);
+        return value;
+    }
+    else if (strEQ(var, "EXTENSIONS") && (clienthello_vars->extids_len > 0)) {
+        value = apr_palloc(p, clienthello_vars->extids_len * 4 + 1);
+        for (i = 0; i < clienthello_vars->extids_len; i++) {
+            apr_snprintf(value + i * 4, 5, "%04x", (uint16_t) clienthello_vars->extids_data[i]);
+        }
+        return value;
+    }
+    else if (strEQ(var, "GROUPS") && (clienthello_vars->ecgroups_len > 2)) {
+        value = apr_palloc(p, clienthello_vars->ecgroups_len * 2 + 1 - 2);
+        ap_bin2hex(clienthello_vars->ecgroups_data + 2, clienthello_vars->ecgroups_len - 2, value);
+        return value;
+    }
+    else if (strEQ(var, "EC_FORMATS") && (clienthello_vars->ecformats_len > 1)) {
+        value = apr_palloc(p, clienthello_vars->ecformats_len * 2 + 1 - 1);
+        ap_bin2hex(clienthello_vars->ecformats_data + 1, clienthello_vars->ecformats_len - 1, value);
+        return value;
+    }
+    else if (strEQ(var, "SIG_ALGOS") && (clienthello_vars->sigalgos_len > 2)) {
+        value = apr_palloc(p, clienthello_vars->sigalgos_len * 2 + 1 - 2);
+        ap_bin2hex(clienthello_vars->sigalgos_data + 2, clienthello_vars->sigalgos_len - 2, value);
+        return value;
+    }
+    else if (strEQ(var, "ALPN") && (clienthello_vars->alpn_len > 2)) {
+        value = apr_palloc(p, clienthello_vars->alpn_len * 2 + 1 - 2);
+        ap_bin2hex(clienthello_vars->alpn_data + 2, clienthello_vars->alpn_len - 2, value);
+        return value;
+    }
+    else if (strEQ(var, "VERSIONS") && (clienthello_vars->versions_len > 1)) {
+        value = apr_palloc(p, clienthello_vars->versions_len * 2 + 1 - 1);
+        ap_bin2hex(clienthello_vars->versions_data + 1, clienthello_vars->versions_len - 1, value);
+        return value;
+    }
+#endif
+    return NULL;
+}
+
 static const char *ssl_var_lookup_ssl_version(const char *var)
 {
     if (strEQ(var, "INTERFACE")) {

modules/ssl/ssl_private.h

@@ -574,6 +574,30 @@ typedef enum {
     SSL_SHUTDOWN_TYPE_ACCURATE
 } ssl_shutdown_type_e;
 
+/**
+ * Define the structure to hold clienthello variables
+ * (later exposed as environment vars)
+ */
+#if OPENSSL_VERSION_NUMBER >= 0x10101000L && !defined(LIBRESSL_VERSION_NUMBER)
+typedef struct {
+    unsigned int version;
+    apr_size_t ciphers_len;
+    const unsigned char *ciphers_data;
+    apr_size_t extids_len;
+    const int *extids_data;
+    apr_size_t ecgroups_len;
+    const unsigned char *ecgroups_data;
+    apr_size_t ecformats_len;
+    const unsigned char *ecformats_data;
+    apr_size_t sigalgos_len;
+    const unsigned char *sigalgos_data;
+    apr_size_t alpn_len;
+    const unsigned char *alpn_data;
+    apr_size_t versions_len;
+    const unsigned char *versions_data;
+} modssl_clienthello_vars;
+#endif
+
 typedef struct {
     SSL *ssl;
     const char *client_dn;
@@ -604,6 +628,10 @@ typedef struct {
     const char *cipher_suite; /* cipher suite used in last reneg */
     int service_unavailable;  /* thouugh we negotiate SSL, no requests will be served */
     int vhost_found;          /* whether we found vhost from SNI already */
+
+#if OPENSSL_VERSION_NUMBER >= 0x10101000L && !defined(LIBRESSL_VERSION_NUMBER)
+    modssl_clienthello_vars *clienthello_vars;  /* info from clienthello callback */
+#endif
 } SSLConnRec;
 
 /* Private keys are retained across reloads, since decryption
@@ -833,7 +861,7 @@ struct SSLSrvConfigRec {
     BOOL             compression;
 #endif
     BOOL             session_tickets;
-    
+    BOOL             clienthello_vars;
 };
 
 /**
@@ -893,6 +921,7 @@ const char  *ssl_cmd_SSLCARevocationPath(cmd_parms *, void *, const char *);
 const char  *ssl_cmd_SSLCARevocationFile(cmd_parms *, void *, const char *);
 const char  *ssl_cmd_SSLCARevocationCheck(cmd_parms *, void *, const char *);
 const char  *ssl_cmd_SSLHonorCipherOrder(cmd_parms *cmd, void *dcfg, int flag);
+const char  *ssl_cmd_SSLClientHelloVars(cmd_parms *, void *, int flag);
 const char  *ssl_cmd_SSLCompression(cmd_parms *, void *, int flag);
 const char  *ssl_cmd_SSLSessionTickets(cmd_parms *, void *, int flag);
 const char  *ssl_cmd_SSLVerifyClient(cmd_parms *, void *, const char *);