Add SSL_CTX early callback

Provide a callback interface that gives the application the ability
to adjust the nascent SSL object at the earliest stage of ClientHello
processing, immediately after extensions have been collected but
before they have been processed.

This is akin to BoringSSL's "select_certificate_cb" (though it is not
API compatible), and as the name indicates, one major use is to examine
the supplied server name indication and select what certificate to
present to the client.  However, it can also be used to make more
sweeping configuration changes to the SSL object according to the
selected server identity and configuration.  That may include adjusting
the permitted TLS versions, swapping out the SSL_CTX object (as is
traditionally done in a tlsext_servername_callback), changing the
server's cipher list, and more.

We also wish to allow an early callback to indicate that it needs to perform
additional work asynchronously and resume processing later.  To that effect,
refactor the second half of tls_process_client_hello() into a subroutine to be
called at the post-processing stage (including the early callback itself), to
allow the callback to result in remaining in the same work stage for a later
call to succeed.  This requires allocating for and storing the CLIENTHELLO_MSG
in the SSL object to be preserved across such calls, but the storage is
reclaimed after ClientHello processing finishes.

Information about the CliehtHello is available to the callback by means of
accessor functions that can only be used from the early callback.  This allows
extensions to make use of the existing internal parsing machinery without
exposing structure internals (e.g., of PACKET), so that applications do not
have to write fragile parsing code.

Applications are encouraged to utilize an early callback and not use
a servername_callback, in order to avoid unexpected behavior that
occurs due to the relative order of processing between things like
session resumption and the historical servername callback.

Also tidy up nearby style by removing unnecessary braces around one-line
conditional bodies.

Reviewed-by: Matt Caswell <matt@openssl.org>
Reviewed-by: Richard Levitte <levitte@openssl.org>
(Merged from https://github.com/openssl/openssl/pull/2279)

4 files changed, 269 insertions, 134 deletions

diff --git a/ssl/ssl_err.c b/ssl/ssl_err.c
index d937ba2c6e..bcb9ddb4f7 100644
--- a/ssl/ssl_err.c
+++ b/ssl/ssl_err.c
@@ -376,6 +376,8 @@ static ERR_STRING_DATA SSL_str_functs[] = {
      "tls_construct_stoc_status_request"},
     {ERR_FUNC(SSL_F_TLS_CONSTRUCT_STOC_USE_SRTP),
      "tls_construct_stoc_use_srtp"},
+    {ERR_FUNC(SSL_F_TLS_EARLY_POST_PROCESS_CLIENT_HELLO),
+     "tls_early_post_process_client_hello"},
     {ERR_FUNC(SSL_F_TLS_GET_MESSAGE_BODY), "tls_get_message_body"},
     {ERR_FUNC(SSL_F_TLS_GET_MESSAGE_HEADER), "tls_get_message_header"},
     {ERR_FUNC(SSL_F_TLS_PARSE_CLIENTHELLO_TLSEXT),
diff --git a/ssl/ssl_lib.c b/ssl/ssl_lib.c
index ff99c0f707..8304c732ae 100644
--- a/ssl/ssl_lib.c
+++ b/ssl/ssl_lib.c
@@ -1014,6 +1014,7 @@ void SSL_free(SSL *s)
 #endif
     OPENSSL_free(s->ext.ocsp.resp);
     OPENSSL_free(s->ext.alpn);
+    OPENSSL_free(s->clienthello);
 
     sk_X509_NAME_pop_free(s->client_CA, X509_NAME_free);
 
@@ -3012,15 +3013,14 @@ int SSL_get_error(const SSL *s, int i)
                 return (SSL_ERROR_SYSCALL);
         }
     }
-    if (SSL_want_x509_lookup(s)) {
+    if (SSL_want_x509_lookup(s))
         return (SSL_ERROR_WANT_X509_LOOKUP);
-    }
-    if (SSL_want_async(s)) {
+    if (SSL_want_async(s))
         return SSL_ERROR_WANT_ASYNC;
-    }
-    if (SSL_want_async_job(s)) {
+    if (SSL_want_async_job(s))
         return SSL_ERROR_WANT_ASYNC_JOB;
-    }
+    if (SSL_want_early(s))
+        return SSL_ERROR_WANT_EARLY;
 
     if ((s->shutdown & SSL_RECEIVED_SHUTDOWN) &&
         (s->s3->warn_alert == SSL_AD_CLOSE_NOTIFY))
@@ -4305,7 +4305,84 @@ const CTLOG_STORE *SSL_CTX_get0_ctlog_store(const SSL_CTX *ctx)
     return ctx->ctlog_store;
 }
 
-#endif
+#endif  /* OPENSSL_NO_CT */
+
+void SSL_CTX_set_early_cb(SSL_CTX *c, SSL_early_cb_fn cb, void *arg)
+{
+    c->early_cb = cb;
+    c->early_cb_arg = arg;
+}
+
+int SSL_early_isv2(SSL *s)
+{
+    if (s->clienthello == NULL)
+        return 0;
+    return s->clienthello->isv2;
+}
+
+unsigned int SSL_early_get0_legacy_version(SSL *s)
+{
+    if (s->clienthello == NULL)
+        return 0;
+    return s->clienthello->legacy_version;
+}
+
+size_t SSL_early_get0_random(SSL *s, const unsigned char **out)
+{
+    if (s->clienthello == NULL)
+        return 0;
+    if (out != NULL)
+        *out = s->clienthello->random;
+    return SSL3_RANDOM_SIZE;
+}
+
+size_t SSL_early_get0_session_id(SSL *s, const unsigned char **out)
+{
+    if (s->clienthello == NULL)
+        return 0;
+    if (out != NULL)
+        *out = s->clienthello->session_id;
+    return s->clienthello->session_id_len;
+}
+
+size_t SSL_early_get0_ciphers(SSL *s, const unsigned char **out)
+{
+    if (s->clienthello == NULL)
+        return 0;
+    if (out != NULL)
+        *out = PACKET_data(&s->clienthello->ciphersuites);
+    return PACKET_remaining(&s->clienthello->ciphersuites);
+}
+
+size_t SSL_early_get0_compression_methods(SSL *s, const unsigned char **out)
+{
+    if (s->clienthello == NULL)
+        return 0;
+    if (out != NULL)
+        *out = s->clienthello->compressions;
+    return s->clienthello->compressions_len;
+}
+
+int SSL_early_get0_ext(SSL *s, unsigned int type, const unsigned char **out,
+                       size_t *outlen)
+{
+    size_t i;
+    RAW_EXTENSION *r;
+
+    if (s->clienthello == NULL)
+        return 0;
+    for (i = 0; i < s->clienthello->pre_proc_exts_len; ++i) {
+        r = s->clienthello->pre_proc_exts + i;
+        if (r->present && r->type == type) {
+            if (out != NULL)
+                *out = PACKET_data(&r->data);
+            if (outlen != NULL)
+                *outlen = PACKET_remaining(&r->data);
+            return 1;
+        }
+    }
+    return 0;
+}
 
 void SSL_CTX_set_keylog_callback(SSL_CTX *ctx, SSL_CTX_keylog_cb_func cb)
 {
diff --git a/ssl/ssl_locl.h b/ssl/ssl_locl.h
index 40bcdd26f2..89eeb45353 100644
--- a/ssl/ssl_locl.h
+++ b/ssl/ssl_locl.h
@@ -830,6 +830,10 @@ struct ssl_ctx_st {
     ENGINE *client_cert_engine;
 # endif
 
+    /* Early callback.  Mostly for extensions, but not entirely. */
+    SSL_early_cb_fn early_cb;
+    void *early_cb_arg;
+
     /* TLS extensions. */
     struct {
         /* TLS extensions servername callback */
@@ -1171,6 +1175,9 @@ struct ssl_st {
         int use_etm;
     } ext;
 
+    /* Parsed form of the ClientHello, kept around across early_cb calls. */
+    CLIENTHELLO_MSG *clienthello;
+
     /*-
      * no further mod of servername
      * 0 : call the servername extension callback.
diff --git a/ssl/statem/statem_srvr.c b/ssl/statem/statem_srvr.c
index 880996b126..9c422e4752 100644
--- a/ssl/statem/statem_srvr.c
+++ b/ssl/statem/statem_srvr.c
@@ -1217,22 +1217,17 @@ static void ssl_check_for_safari(SSL *s, const CLIENTHELLO_MSG *hello)
 
 MSG_PROCESS_RETURN tls_process_client_hello(SSL *s, PACKET *pkt)
 {
-    int i, al = SSL_AD_INTERNAL_ERROR;
-    unsigned int j;
-    size_t loop;
-    unsigned long id;
-    const SSL_CIPHER *c;
-#ifndef OPENSSL_NO_COMP
-    SSL_COMP *comp = NULL;
-#endif
-    STACK_OF(SSL_CIPHER) *ciphers = NULL;
-    STACK_OF(SSL_CIPHER) *scsvs = NULL;
-    int protverr;
+    int al = SSL_AD_INTERNAL_ERROR;
     /* |cookie| will only be initialized for DTLS. */
     PACKET session_id, compression, extensions, cookie;
     static const unsigned char null_compression = 0;
-    CLIENTHELLO_MSG clienthello;
+    CLIENTHELLO_MSG *clienthello;
 
+    clienthello = OPENSSL_zalloc(sizeof(*clienthello));
+    if (clienthello == NULL) {
+        SSLerr(SSL_F_TLS_PROCESS_CLIENT_HELLO, ERR_R_INTERNAL_ERROR);
+        goto err;
+    }
     /* Check if this is actually an unexpected renegotiation ClientHello */
     if (s->renegotiate == 0 && !SSL_IS_FIRST_HANDSHAKE(s)) {
         s->renegotiate = 1;
@@ -1245,11 +1240,10 @@ MSG_PROCESS_RETURN tls_process_client_hello(SSL *s, PACKET *pkt)
     /*
      * First, parse the raw ClientHello data into the CLIENTHELLO_MSG structure.
      */
-    memset(&clienthello, 0, sizeof(clienthello));
-    clienthello.isv2 = RECORD_LAYER_is_sslv2_record(&s->rlayer);
+    clienthello->isv2 = RECORD_LAYER_is_sslv2_record(&s->rlayer);
     PACKET_null_init(&cookie);
 
-    if (clienthello.isv2) {
+    if (clienthello->isv2) {
         unsigned int mt;
 
         if (!SSL_IS_FIRST_HANDSHAKE(s) || s->hello_retry_request) {
@@ -1285,14 +1279,14 @@ MSG_PROCESS_RETURN tls_process_client_hello(SSL *s, PACKET *pkt)
         }
     }
 
-    if (!PACKET_get_net_2(pkt, &clienthello.legacy_version)) {
+    if (!PACKET_get_net_2(pkt, &clienthello->legacy_version)) {
         al = SSL_AD_DECODE_ERROR;
         SSLerr(SSL_F_TLS_PROCESS_CLIENT_HELLO, SSL_R_LENGTH_TOO_SHORT);
         goto err;
     }
 
     /* Parse the message and load client random. */
-    if (clienthello.isv2) {
+    if (clienthello->isv2) {
         /*
          * Handle an SSLv2 backwards compatible ClientHello
          * Note, this is only for SSLv3+ using the backward compatible format.
@@ -1316,9 +1310,9 @@ MSG_PROCESS_RETURN tls_process_client_hello(SSL *s, PACKET *pkt)
             goto f_err;
         }
 
-        if (!PACKET_get_sub_packet(pkt, &clienthello.ciphersuites,
+        if (!PACKET_get_sub_packet(pkt, &clienthello->ciphersuites,
                                    ciphersuite_len)
-            || !PACKET_copy_bytes(pkt, clienthello.session_id, session_id_len)
+            || !PACKET_copy_bytes(pkt, clienthello->session_id, session_id_len)
             || !PACKET_get_sub_packet(pkt, &challenge, challenge_len)
             /* No extensions. */
             || PACKET_remaining(pkt) != 0) {
@@ -1327,18 +1321,18 @@ MSG_PROCESS_RETURN tls_process_client_hello(SSL *s, PACKET *pkt)
             al = SSL_AD_DECODE_ERROR;
             goto f_err;
         }
-        clienthello.session_id_len = session_id_len;
+        clienthello->session_id_len = session_id_len;
 
         /* Load the client random and compression list. We use SSL3_RANDOM_SIZE
-         * here rather than sizeof(clienthello.random) because that is the limit
+         * here rather than sizeof(clienthello->random) because that is the limit
          * for SSLv3 and it is fixed. It won't change even if
-         * sizeof(clienthello.random) does.
+         * sizeof(clienthello->random) does.
          */
         challenge_len = challenge_len > SSL3_RANDOM_SIZE
                         ? SSL3_RANDOM_SIZE : challenge_len;
-        memset(clienthello.random, 0, SSL3_RANDOM_SIZE);
+        memset(clienthello->random, 0, SSL3_RANDOM_SIZE);
         if (!PACKET_copy_bytes(&challenge,
-                               clienthello.random + SSL3_RANDOM_SIZE -
+                               clienthello->random + SSL3_RANDOM_SIZE -
                                challenge_len, challenge_len)
             /* Advertise only null compression. */
             || !PACKET_buf_init(&compression, &null_compression, 1)) {
@@ -1347,14 +1341,14 @@ MSG_PROCESS_RETURN tls_process_client_hello(SSL *s, PACKET *pkt)
             goto f_err;
         }
 
-        PACKET_null_init(&clienthello.extensions);
+        PACKET_null_init(&clienthello->extensions);
     } else {
         /* Regular ClientHello. */
-        if (!PACKET_copy_bytes(pkt, clienthello.random, SSL3_RANDOM_SIZE)
+        if (!PACKET_copy_bytes(pkt, clienthello->random, SSL3_RANDOM_SIZE)
             || !PACKET_get_length_prefixed_1(pkt, &session_id)
-            || !PACKET_copy_all(&session_id, clienthello.session_id,
+            || !PACKET_copy_all(&session_id, clienthello->session_id,
                     SSL_MAX_SSL_SESSION_ID_LENGTH,
-                    &clienthello.session_id_len)) {
+                    &clienthello->session_id_len)) {
             al = SSL_AD_DECODE_ERROR;
             SSLerr(SSL_F_TLS_PROCESS_CLIENT_HELLO, SSL_R_LENGTH_MISMATCH);
             goto f_err;
@@ -1366,9 +1360,9 @@ MSG_PROCESS_RETURN tls_process_client_hello(SSL *s, PACKET *pkt)
                 SSLerr(SSL_F_TLS_PROCESS_CLIENT_HELLO, SSL_R_LENGTH_MISMATCH);
                 goto f_err;
             }
-            if (!PACKET_copy_all(&cookie, clienthello.dtls_cookie,
+            if (!PACKET_copy_all(&cookie, clienthello->dtls_cookie,
                                  DTLS1_COOKIE_LENGTH,
-                                 &clienthello.dtls_cookie_len)) {
+                                 &clienthello->dtls_cookie_len)) {
                 al = SSL_AD_DECODE_ERROR;
                 SSLerr(SSL_F_TLS_PROCESS_CLIENT_HELLO, SSL_R_LENGTH_MISMATCH);
                 goto f_err;
@@ -1379,12 +1373,12 @@ MSG_PROCESS_RETURN tls_process_client_hello(SSL *s, PACKET *pkt)
              * So check cookie length...
              */
             if (SSL_get_options(s) & SSL_OP_COOKIE_EXCHANGE) {
-                if (clienthello.dtls_cookie_len == 0)
+                if (clienthello->dtls_cookie_len == 0)
                     return 1;
             }
         }
 
-        if (!PACKET_get_length_prefixed_2(pkt, &clienthello.ciphersuites)) {
+        if (!PACKET_get_length_prefixed_2(pkt, &clienthello->ciphersuites)) {
             al = SSL_AD_DECODE_ERROR;
             SSLerr(SSL_F_TLS_PROCESS_CLIENT_HELLO, SSL_R_LENGTH_MISMATCH);
             goto f_err;
@@ -1398,9 +1392,9 @@ MSG_PROCESS_RETURN tls_process_client_hello(SSL *s, PACKET *pkt)
 
         /* Could be empty. */
         if (PACKET_remaining(pkt) == 0) {
-            PACKET_null_init(&clienthello.extensions);
+            PACKET_null_init(&clienthello->extensions);
         } else {
-            if (!PACKET_get_length_prefixed_2(pkt, &clienthello.extensions)) {
+            if (!PACKET_get_length_prefixed_2(pkt, &clienthello->extensions)) {
                 al = SSL_AD_DECODE_ERROR;
                 SSLerr(SSL_F_TLS_PROCESS_CLIENT_HELLO, SSL_R_LENGTH_MISMATCH);
                 goto f_err;
@@ -1408,96 +1402,137 @@ MSG_PROCESS_RETURN tls_process_client_hello(SSL *s, PACKET *pkt)
         }
     }
 
-    if (!PACKET_copy_all(&compression, clienthello.compressions,
+    if (!PACKET_copy_all(&compression, clienthello->compressions,
                          MAX_COMPRESSIONS_SIZE,
-                         &clienthello.compressions_len)) {
+                         &clienthello->compressions_len)) {
         al = SSL_AD_DECODE_ERROR;
         SSLerr(SSL_F_TLS_PROCESS_CLIENT_HELLO, SSL_R_LENGTH_MISMATCH);
         goto f_err;
     }
 
     /* Preserve the raw extensions PACKET for later use */
-    extensions = clienthello.extensions;
+    extensions = clienthello->extensions;
     if (!tls_collect_extensions(s, &extensions, EXT_CLIENT_HELLO,
-                                &clienthello.pre_proc_exts, &al,
-                                &clienthello.pre_proc_exts_len)) {
+                                &clienthello->pre_proc_exts, &al,
+                                &clienthello->pre_proc_exts_len)) {
         /* SSLerr already been called */
         goto f_err;
     }
+    s->clienthello = clienthello;
 
+    return MSG_PROCESS_CONTINUE_PROCESSING;
+ f_err:
+    ssl3_send_alert(s, SSL3_AL_FATAL, al);
+ err:
+    ossl_statem_set_error(s);
+
+    OPENSSL_free(clienthello->pre_proc_exts);
+    OPENSSL_free(clienthello);
+
+    return MSG_PROCESS_ERROR;
+}
+
+static int tls_early_post_process_client_hello(SSL *s, int *al)
+{
+    unsigned int j;
+    int i;
+    int protverr;
+    size_t loop;
+    unsigned long id;
+#ifndef OPENSSL_NO_COMP
+    SSL_COMP *comp = NULL;
+#endif
+    const SSL_CIPHER *c;
+    STACK_OF(SSL_CIPHER) *ciphers = NULL;
+    STACK_OF(SSL_CIPHER) *scsvs = NULL;
+    CLIENTHELLO_MSG *clienthello = s->clienthello;
+
+    *al = SSL_AD_INTERNAL_ERROR;
     /* Finished parsing the ClientHello, now we can start processing it */
+    /* Give the early callback a crack at things */
+    if (s->ctx->early_cb != NULL) {
+        int code;
+        /* A failure in the early callback terminates the connection. */
+        code = s->ctx->early_cb(s, al, s->ctx->early_cb_arg);
+        if (code == 0)
+            goto err;
+        if (code < 0) {
+            s->rwstate = SSL_EARLY_WORK;
+            return code;
+        }
+    }
 
     /* Set up the client_random */
-    memcpy(s->s3->client_random, clienthello.random, SSL3_RANDOM_SIZE);
+    memcpy(s->s3->client_random, clienthello->random, SSL3_RANDOM_SIZE);
 
     /* Choose the version */
 
-    if (clienthello.isv2) {
-        if (clienthello.legacy_version == SSL2_VERSION
-                || (clienthello.legacy_version & 0xff00)
+    if (clienthello->isv2) {
+        if (clienthello->legacy_version == SSL2_VERSION
+                || (clienthello->legacy_version & 0xff00)
                    != (SSL3_VERSION_MAJOR << 8)) {
             /*
              * This is real SSLv2 or something complete unknown. We don't
              * support it.
              */
-            SSLerr(SSL_F_TLS_PROCESS_CLIENT_HELLO, SSL_R_UNKNOWN_PROTOCOL);
+            SSLerr(SSL_F_TLS_EARLY_POST_PROCESS_CLIENT_HELLO, SSL_R_UNKNOWN_PROTOCOL);
             goto err;
         }
         /* SSLv3/TLS */
-        s->client_version = clienthello.legacy_version;
+        s->client_version = clienthello->legacy_version;
     }
     /*
      * Do SSL/TLS version negotiation if applicable. For DTLS we just check
      * versions are potentially compatible. Version negotiation comes later.
      */
     if (!SSL_IS_DTLS(s)) {
-        protverr = ssl_choose_server_version(s, &clienthello);
+        protverr = ssl_choose_server_version(s, clienthello);
     } else if (s->method->version != DTLS_ANY_VERSION &&
-               DTLS_VERSION_LT((int)clienthello.legacy_version, s->version)) {
+               DTLS_VERSION_LT((int)clienthello->legacy_version, s->version)) {
         protverr = SSL_R_VERSION_TOO_LOW;
     } else {
         protverr = 0;
     }
 
     if (protverr) {
-        SSLerr(SSL_F_TLS_PROCESS_CLIENT_HELLO, protverr);
+        SSLerr(SSL_F_TLS_EARLY_POST_PROCESS_CLIENT_HELLO, protverr);
         if (SSL_IS_FIRST_HANDSHAKE(s)) {
             /* like ssl3_get_record, send alert using remote version number */
-            s->version = s->client_version = clienthello.legacy_version;
+            s->version = s->client_version = clienthello->legacy_version;
         }
-        al = SSL_AD_PROTOCOL_VERSION;
-        goto f_err;
+        *al = SSL_AD_PROTOCOL_VERSION;
+        goto err;
     }
 
     if (SSL_IS_DTLS(s)) {
         /* Empty cookie was already handled above by returning early. */
         if (SSL_get_options(s) & SSL_OP_COOKIE_EXCHANGE) {
             if (s->ctx->app_verify_cookie_cb != NULL) {
-                if (s->ctx->app_verify_cookie_cb(s, clienthello.dtls_cookie,
-                        clienthello.dtls_cookie_len) == 0) {
-                    al = SSL_AD_HANDSHAKE_FAILURE;
-                    SSLerr(SSL_F_TLS_PROCESS_CLIENT_HELLO,
+                if (s->ctx->app_verify_cookie_cb(s, clienthello->dtls_cookie,
+                        clienthello->dtls_cookie_len) == 0) {
+                    *al = SSL_AD_HANDSHAKE_FAILURE;
+                    SSLerr(SSL_F_TLS_EARLY_POST_PROCESS_CLIENT_HELLO,
                            SSL_R_COOKIE_MISMATCH);
-                    goto f_err;
+                    goto err;
                     /* else cookie verification succeeded */
                 }
                 /* default verification */
-            } else if (s->d1->cookie_len != clienthello.dtls_cookie_len
-                    || memcmp(clienthello.dtls_cookie, s->d1->cookie,
+            } else if (s->d1->cookie_len != clienthello->dtls_cookie_len
+                    || memcmp(clienthello->dtls_cookie, s->d1->cookie,
                               s->d1->cookie_len) != 0) {
-                al = SSL_AD_HANDSHAKE_FAILURE;
-                SSLerr(SSL_F_TLS_PROCESS_CLIENT_HELLO, SSL_R_COOKIE_MISMATCH);
-                goto f_err;
+                *al = SSL_AD_HANDSHAKE_FAILURE;
+                SSLerr(SSL_F_TLS_EARLY_POST_PROCESS_CLIENT_HELLO, SSL_R_COOKIE_MISMATCH);
+                goto err;
             }
             s->d1->cookie_verified = 1;
         }
         if (s->method->version == DTLS_ANY_VERSION) {
-            protverr = ssl_choose_server_version(s, &clienthello);
+            protverr = ssl_choose_server_version(s, clienthello);
             if (protverr != 0) {
-                SSLerr(SSL_F_TLS_PROCESS_CLIENT_HELLO, protverr);
+                SSLerr(SSL_F_TLS_EARLY_POST_PROCESS_CLIENT_HELLO, protverr);
                 s->version = s->client_version;
-                al = SSL_AD_PROTOCOL_VERSION;
-                goto f_err;
+                *al = SSL_AD_PROTOCOL_VERSION;
+                goto err;
             }
         }
     }
@@ -1507,9 +1542,9 @@ MSG_PROCESS_RETURN tls_process_client_hello(SSL *s, PACKET *pkt)
     /* We need to do this before getting the session */
     if (!tls_parse_extension(s, TLSEXT_IDX_extended_master_secret,
                              EXT_CLIENT_HELLO,
-                             clienthello.pre_proc_exts, NULL, 0, &al)) {
-        SSLerr(SSL_F_TLS_PROCESS_CLIENT_HELLO, SSL_R_CLIENTHELLO_TLSEXT);
-        goto f_err;
+                             clienthello->pre_proc_exts, NULL, 0, al)) {
+        SSLerr(SSL_F_TLS_EARLY_POST_PROCESS_CLIENT_HELLO, SSL_R_CLIENTHELLO_TLSEXT);
+        goto err;
     }
 
     /*
@@ -1528,18 +1563,18 @@ MSG_PROCESS_RETURN tls_process_client_hello(SSL *s, PACKET *pkt)
      * SSL_OP_NO_SESSION_RESUMPTION_ON_RENEGOTIATION setting will be
      * ignored.
      */
-    if (clienthello.isv2 ||
+    if (clienthello->isv2 ||
         (s->new_session &&
          (s->options & SSL_OP_NO_SESSION_RESUMPTION_ON_RENEGOTIATION))) {
         if (!ssl_get_new_session(s, 1))
             goto err;
     } else {
-        i = ssl_get_prev_session(s, &clienthello, &al);
+        i = ssl_get_prev_session(s, clienthello, al);
         if (i == 1) {
             /* previous session */
             s->hit = 1;
         } else if (i == -1) {
-            goto f_err;
+            goto err;
         } else {
             /* i == 0 */
             if (!ssl_get_new_session(s, 1))
@@ -1547,11 +1582,11 @@ MSG_PROCESS_RETURN tls_process_client_hello(SSL *s, PACKET *pkt)
         }
     }
 
-    if (!ssl_cache_cipherlist(s, &clienthello.ciphersuites,
-                              clienthello.isv2, &al) ||
-        !bytes_to_cipher_list(s, &clienthello.ciphersuites, &ciphers, &scsvs,
-                             clienthello.isv2, &al)) {
-        goto f_err;
+    if (!ssl_cache_cipherlist(s, &clienthello->ciphersuites,
+                              clienthello->isv2, al) ||
+        !bytes_to_cipher_list(s, &clienthello->ciphersuites, &ciphers, &scsvs,
+                             clienthello->isv2, al)) {
+        goto err;
     }
 
     s->s3->send_connection_binding = 0;
@@ -1562,10 +1597,10 @@ MSG_PROCESS_RETURN tls_process_client_hello(SSL *s, PACKET *pkt)
             if (SSL_CIPHER_get_id(c) == SSL3_CK_SCSV) {
                 if (s->renegotiate) {
                     /* SCSV is fatal if renegotiating */
-                    SSLerr(SSL_F_TLS_PROCESS_CLIENT_HELLO,
+                    SSLerr(SSL_F_TLS_EARLY_POST_PROCESS_CLIENT_HELLO,
                            SSL_R_SCSV_RECEIVED_WHEN_RENEGOTIATING);
-                    al = SSL_AD_HANDSHAKE_FAILURE;
-                    goto f_err;
+                    *al = SSL_AD_HANDSHAKE_FAILURE;
+                    goto err;
                 }
                 s->s3->send_connection_binding = 1;
             } else if (SSL_CIPHER_get_id(c) == SSL3_CK_FALLBACK_SCSV &&
@@ -1577,10 +1612,10 @@ MSG_PROCESS_RETURN tls_process_client_hello(SSL *s, PACKET *pkt)
                  * connection may have been tampered with in order to trigger
                  * an insecure downgrade.
                  */
-                SSLerr(SSL_F_TLS_PROCESS_CLIENT_HELLO,
+                SSLerr(SSL_F_TLS_EARLY_POST_PROCESS_CLIENT_HELLO,
                        SSL_R_INAPPROPRIATE_FALLBACK);
-                al = SSL_AD_INAPPROPRIATE_FALLBACK;
-                goto f_err;
+                *al = SSL_AD_INAPPROPRIATE_FALLBACK;
+                goto err;
             }
         }
     }
@@ -1609,35 +1644,35 @@ MSG_PROCESS_RETURN tls_process_client_hello(SSL *s, PACKET *pkt)
              * we need to have the cipher in the cipher list if we are asked
              * to reuse it
              */
-            al = SSL_AD_ILLEGAL_PARAMETER;
-            SSLerr(SSL_F_TLS_PROCESS_CLIENT_HELLO,
+            *al = SSL_AD_ILLEGAL_PARAMETER;
+            SSLerr(SSL_F_TLS_EARLY_POST_PROCESS_CLIENT_HELLO,
                    SSL_R_REQUIRED_CIPHER_MISSING);
-            goto f_err;
+            goto err;
         }
     }
 
-    for (loop = 0; loop < clienthello.compressions_len; loop++) {
-        if (clienthello.compressions[loop] == 0)
+    for (loop = 0; loop < clienthello->compressions_len; loop++) {
+        if (clienthello->compressions[loop] == 0)
             break;
     }
 
-    if (loop >= clienthello.compressions_len) {
+    if (loop >= clienthello->compressions_len) {
         /* no compress */
-        al = SSL_AD_DECODE_ERROR;
-        SSLerr(SSL_F_TLS_PROCESS_CLIENT_HELLO, SSL_R_NO_COMPRESSION_SPECIFIED);
-        goto f_err;
+        *al = SSL_AD_DECODE_ERROR;
+        SSLerr(SSL_F_TLS_EARLY_POST_PROCESS_CLIENT_HELLO, SSL_R_NO_COMPRESSION_SPECIFIED);
+        goto err;
     }
 
 #ifndef OPENSSL_NO_EC
     if (s->options & SSL_OP_SAFARI_ECDHE_ECDSA_BUG)
-        ssl_check_for_safari(s, &clienthello);
+        ssl_check_for_safari(s, clienthello);
 #endif                          /* !OPENSSL_NO_EC */
 
     /* TLS extensions */
     if (!tls_parse_all_extensions(s, EXT_CLIENT_HELLO,
-                                  clienthello.pre_proc_exts, NULL, 0, &al)) {
-        SSLerr(SSL_F_TLS_PROCESS_CLIENT_HELLO, SSL_R_PARSE_TLSEXT);
-        goto f_err;
+                                  clienthello->pre_proc_exts, NULL, 0, al)) {
+        SSLerr(SSL_F_TLS_EARLY_POST_PROCESS_CLIENT_HELLO, SSL_R_PARSE_TLSEXT);
+        goto err;
     }
 
     /*
@@ -1650,7 +1685,7 @@ MSG_PROCESS_RETURN tls_process_client_hello(SSL *s, PACKET *pkt)
         unsigned char *pos;
         pos = s->s3->server_random;
         if (ssl_fill_hello_random(s, 1, pos, SSL3_RANDOM_SIZE) <= 0) {
-            goto f_err;
+            goto err;
         }
     }
 
@@ -1680,9 +1715,9 @@ MSG_PROCESS_RETURN tls_process_client_hello(SSL *s, PACKET *pkt)
                 pref_cipher = ssl3_choose_cipher(s, s->session->ciphers,
                                                  SSL_get_ciphers(s));
             if (pref_cipher == NULL) {
-                al = SSL_AD_HANDSHAKE_FAILURE;
-                SSLerr(SSL_F_TLS_PROCESS_CLIENT_HELLO, SSL_R_NO_SHARED_CIPHER);
-                goto f_err;
+                *al = SSL_AD_HANDSHAKE_FAILURE;
+                SSLerr(SSL_F_TLS_EARLY_POST_PROCESS_CLIENT_HELLO, SSL_R_NO_SHARED_CIPHER);
+                goto err;
             }
 
             s->session->cipher = pref_cipher;
@@ -1707,9 +1742,9 @@ MSG_PROCESS_RETURN tls_process_client_hello(SSL *s, PACKET *pkt)
         /* Perform sanity checks on resumed compression algorithm */
         /* Can't disable compression */
         if (!ssl_allow_compression(s)) {
-            SSLerr(SSL_F_TLS_PROCESS_CLIENT_HELLO,
+            SSLerr(SSL_F_TLS_EARLY_POST_PROCESS_CLIENT_HELLO,
                    SSL_R_INCONSISTENT_COMPRESSION);
-            goto f_err;
+            goto err;
         }
         /* Look for resumed compression method */
         for (m = 0; m < sk_SSL_COMP_num(s->ctx->comp_methods); m++) {
@@ -1720,20 +1755,20 @@ MSG_PROCESS_RETURN tls_process_client_hello(SSL *s, PACKET *pkt)
             }
         }
         if (s->s3->tmp.new_compression == NULL) {
-            SSLerr(SSL_F_TLS_PROCESS_CLIENT_HELLO,
+            SSLerr(SSL_F_TLS_EARLY_POST_PROCESS_CLIENT_HELLO,
                    SSL_R_INVALID_COMPRESSION_ALGORITHM);
-            goto f_err;
+            goto err;
         }
         /* Look for resumed method in compression list */
-        for (k = 0; k < clienthello.compressions_len; k++) {
-            if (clienthello.compressions[k] == comp_id)
+        for (k = 0; k < clienthello->compressions_len; k++) {
+            if (clienthello->compressions[k] == comp_id)
                 break;
         }
-        if (k >= clienthello.compressions_len) {
-            al = SSL_AD_ILLEGAL_PARAMETER;
-            SSLerr(SSL_F_TLS_PROCESS_CLIENT_HELLO,
+        if (k >= clienthello->compressions_len) {
+            *al = SSL_AD_ILLEGAL_PARAMETER;
+            SSLerr(SSL_F_TLS_EARLY_POST_PROCESS_CLIENT_HELLO,
                    SSL_R_REQUIRED_COMPRESSION_ALGORITHM_MISSING);
-            goto f_err;
+            goto err;
         }
     } else if (s->hit)
         comp = NULL;
@@ -1746,8 +1781,8 @@ MSG_PROCESS_RETURN tls_process_client_hello(SSL *s, PACKET *pkt)
         for (m = 0; m < nn; m++) {
             comp = sk_SSL_COMP_value(s->ctx->comp_methods, m);
             v = comp->id;
-            for (o = 0; o < clienthello.compressions_len; o++) {
-                if (v == clienthello.compressions[o]) {
+            for (o = 0; o < clienthello->compressions_len; o++) {
+                if (v == clienthello->compressions[o]) {
                     done = 1;
                     break;
                 }
@@ -1766,8 +1801,8 @@ MSG_PROCESS_RETURN tls_process_client_hello(SSL *s, PACKET *pkt)
      * using compression.
      */
     if (s->session->compress_meth != 0) {
-        SSLerr(SSL_F_TLS_PROCESS_CLIENT_HELLO, SSL_R_INCONSISTENT_COMPRESSION);
-        goto f_err;
+        SSLerr(SSL_F_TLS_EARLY_POST_PROCESS_CLIENT_HELLO, SSL_R_INCONSISTENT_COMPRESSION);
+        goto err;
     }
 #endif
 
@@ -1784,29 +1819,33 @@ MSG_PROCESS_RETURN tls_process_client_hello(SSL *s, PACKET *pkt)
         sk_SSL_CIPHER_free(s->session->ciphers);
         s->session->ciphers = ciphers;
         if (ciphers == NULL) {
-            al = SSL_AD_INTERNAL_ERROR;
-            SSLerr(SSL_F_TLS_PROCESS_CLIENT_HELLO, ERR_R_INTERNAL_ERROR);
-            goto f_err;
+            *al = SSL_AD_INTERNAL_ERROR;
+            SSLerr(SSL_F_TLS_EARLY_POST_PROCESS_CLIENT_HELLO, ERR_R_INTERNAL_ERROR);
+            goto err;
         }
         ciphers = NULL;
         if (!tls1_set_server_sigalgs(s)) {
-            SSLerr(SSL_F_TLS_PROCESS_CLIENT_HELLO, SSL_R_CLIENTHELLO_TLSEXT);
+            SSLerr(SSL_F_TLS_EARLY_POST_PROCESS_CLIENT_HELLO, SSL_R_CLIENTHELLO_TLSEXT);
             goto err;
         }
     }
 
     sk_SSL_CIPHER_free(ciphers);
-    OPENSSL_free(clienthello.pre_proc_exts);
-    return MSG_PROCESS_CONTINUE_PROCESSING;
- f_err:
-    ssl3_send_alert(s, SSL3_AL_FATAL, al);
+    sk_SSL_CIPHER_free(scsvs);
+    OPENSSL_free(clienthello->pre_proc_exts);
+    OPENSSL_free(s->clienthello);
+    s->clienthello = NULL;
+    return 1;
  err:
     ossl_statem_set_error(s);
 
     sk_SSL_CIPHER_free(ciphers);
-    OPENSSL_free(clienthello.pre_proc_exts);
+    sk_SSL_CIPHER_free(scsvs);
+    OPENSSL_free(clienthello->pre_proc_exts);
+    OPENSSL_free(s->clienthello);
+    s->clienthello = NULL;
 
-    return MSG_PROCESS_ERROR;
+    return 0;
 }
 
 /*
@@ -1863,6 +1902,16 @@ WORK_STATE tls_post_process_client_hello(SSL *s, WORK_STATE wst)
     const SSL_CIPHER *cipher;
 
     if (wst == WORK_MORE_A) {
+        int rv = tls_early_post_process_client_hello(s, &al);
+        if (rv == 0) {
+            /* SSLErr() was already called */
+            goto f_err;
+        }
+        if (rv < 0)
+            return WORK_MORE_A;
+        wst = WORK_MORE_B;
+    }
+    if (wst == WORK_MORE_B) {
         if (!s->hit) {
             /* Let cert callback update server certificates if required */
             if (s->cert->cert_cb) {
@@ -1875,7 +1924,7 @@ WORK_STATE tls_post_process_client_hello(SSL *s, WORK_STATE wst)
                 }
                 if (rv < 0) {
                     s->rwstate = SSL_X509_LOOKUP;
-                    return WORK_MORE_A;
+                    return WORK_MORE_B;
                 }
                 s->rwstate = SSL_NOTHING;
             }
@@ -1926,17 +1975,17 @@ WORK_STATE tls_post_process_client_hello(SSL *s, WORK_STATE wst)
             goto f_err;
         }
 
-        wst = WORK_MORE_B;
+        wst = WORK_MORE_C;
     }
 #ifndef OPENSSL_NO_SRP
-    if (wst == WORK_MORE_B) {
+    if (wst == WORK_MORE_C) {
         int ret;
         if ((ret = ssl_check_srp_ext_ClientHello(s, &al)) < 0) {
             /*
              * callback indicates further work to be done
              */
             s->rwstate = SSL_X509_LOOKUP;
-            return WORK_MORE_B;
+            return WORK_MORE_C;
         }
         if (ret != SSL_ERROR_NONE) {
             /*