Add SSL_early_get1_extensions_present()

It is an API to be used from the early callback that indicates what
extensions were present in the ClientHello, and in what order.
This can be used to eliminate unneeded calls to SSL_early_get0_ext()
(which itself scales linearly in the number of extensions supported
by the library).

Reviewed-by: Matt Caswell <matt@openssl.org>
(Merged from https://github.com/openssl/openssl/pull/2976)

doc/man3/SSL_CTX_set_early_cb.pod

@@ -2,7 +2,7 @@
 
 =head1 NAME
 
-SSL_CTX_set_early_cb, SSL_early_cb_fn, SSL_early_isv2, SSL_early_get0_legacy_version, SSL_early_get0_random, SSL_early_get0_session_id, SSL_early_get0_ciphers, SSL_early_get0_compression_methods, SSL_early_get0_ext - callback functions for early server-side ClientHello processing
+SSL_CTX_set_early_cb, SSL_early_cb_fn, SSL_early_isv2, SSL_early_get0_legacy_version, SSL_early_get0_random, SSL_early_get0_session_id, SSL_early_get0_ciphers, SSL_early_get0_compression_methods, SSL_early_get1_extensions_present, SSL_early_get0_ext - callback functions for early server-side ClientHello processing
 
 =head1 SYNOPSIS
 
@@ -14,6 +14,7 @@ SSL_CTX_set_early_cb, SSL_early_cb_fn, SSL_early_isv2, SSL_early_get0_legacy_ver
  size_t SSL_early_get0_session_id(SSL *s, const unsigned char **out);
  size_t SSL_early_get0_ciphers(SSL *s, const unsigned char **out);
  size_t SSL_early_get0_compression_methods(SSL *s, const unsigned char **out);
+ int SSL_early_get1_extensions_present(SSL *s, int **out, size_t *outlen);
  int SSL_early_get0_ext(SSL *s, int type, const unsigned char **out,
                         size_t *outlen);
 
@@ -53,6 +54,14 @@ from the ClientHello on a per-extension basis.  For the provided wire
 protocol extension type value, the extension value and length are returned
 in the output parameters (if present).
 
+SSL_early_get1_extensions_present() can be used prior to SSL_early_get0_ext(),
+to determine which extensions are present in the ClientHello before querying
+for them.  The B<out> and B<outlen> parameters are both required, and on
+success the caller must release the storage allocated for B<*out> using
+OPENSSL_free().  The contents of B<*out> is an array of integers holding the
+numerical value of the TLS extension types in the order they appear in the
+ClientHello.  B<*outlen> contains the number of elements in the array.
+
 =head1 NOTES
 
 The early callback provides a vast window of possibilities for application
@@ -88,6 +97,8 @@ assumed to be valid.
 SSL_early_get0_ext() returns 1 if the extension of type 'type' is present, and
 0 otherwise.
 
+SSL_early_get1_extensions_present() returns 1 on success and 0 on failure.
+
 =head1 SEE ALSO
 
 L<ssl(7)>, L<SSL_CTX_set_tlsext_servername_callback(3)>,
@@ -97,8 +108,8 @@ L<SSL_bytes_to_cipher_list>
 
 The SSL early callback, SSL_early_isv2(), SSL_early_get0_random(),
 SSL_early_get0_session_id(), SSL_early_get0_ciphers(),
-SSL_early_get0_compression_methods(), and SSL_early_get0_ext() were
+SSL_early_get0_compression_methods(), SSL_early_get0_ext(), and
-added in OpenSSL 1.1.1.
+SSL_early_get1_extensions_present() were added in OpenSSL 1.1.1.
 
 =head1 COPYRIGHT
 

include/openssl/ssl.h

@@ -1682,6 +1682,7 @@ size_t SSL_early_get0_random(SSL *s, const unsigned char **out);
 size_t SSL_early_get0_session_id(SSL *s, const unsigned char **out);
 size_t SSL_early_get0_ciphers(SSL *s, const unsigned char **out);
 size_t SSL_early_get0_compression_methods(SSL *s, const unsigned char **out);
+int SSL_early_get1_extensions_present(SSL *s, int **out, size_t *outlen);
 int SSL_early_get0_ext(SSL *s, unsigned int type, const unsigned char **out,
                        size_t *outlen);
 

ssl/ssl_lib.c

@@ -4598,6 +4598,38 @@ size_t SSL_early_get0_compression_methods(SSL *s, const unsigned char **out)
     return s->clienthello->compressions_len;
 }
 
+int SSL_early_get1_extensions_present(SSL *s, int **out, size_t *outlen)
+{
+    RAW_EXTENSION *ext;
+    int *present;
+    size_t num = 0, i;
+
+    if (s->clienthello == NULL || out == NULL || outlen == NULL)
+        return 0;
+    for (i = 0; i < s->clienthello->pre_proc_exts_len; i++) {
+        ext = s->clienthello->pre_proc_exts + i;
+        if (ext->present)
+            num++;
+    }
+    present = OPENSSL_malloc(sizeof(*present) * num);
+    if (present == NULL)
+        return 0;
+    for (i = 0; i < s->clienthello->pre_proc_exts_len; i++) {
+        ext = s->clienthello->pre_proc_exts + i;
+        if (ext->present) {
+            if (ext->received_order >= num)
+                goto err;
+            present[ext->received_order] = ext->type;
+        }
+    }
+    *out = present;
+    *outlen = num;
+    return 1;
+ err:
+    OPENSSL_free(present);
+    return 0;
+}
+
 int SSL_early_get0_ext(SSL *s, unsigned int type, const unsigned char **out,
                        size_t *outlen)
 {

ssl/ssl_locl.h

@@ -668,6 +668,8 @@ typedef struct raw_extension_st {
     int parsed;
     /* The type of this extension, i.e. a TLSEXT_TYPE_* value */
     unsigned int type;
+    /* Track what order extensions are received in (0-based). */
+    size_t received_order;
 } RAW_EXTENSION;
 
 typedef struct {

ssl/statem/extensions.c

@@ -462,6 +462,7 @@ int tls_collect_extensions(SSL *s, PACKET *packet, unsigned int context,
         return 0;
     }
 
+    i = 0;
     while (PACKET_remaining(&extensions) > 0) {
         unsigned int type, idx;
         PACKET extension;
@@ -518,6 +519,7 @@ int tls_collect_extensions(SSL *s, PACKET *packet, unsigned int context,
             thisex->data = extension;
             thisex->present = 1;
             thisex->type = type;
+            thisex->received_order = i++;
         }
     }
 

util/libssl.num

@@ -450,3 +450,4 @@ SSL_set_block_padding                   450	1_1_1	EXIST::FUNCTION:
 SSL_set_record_padding_callback_arg     451	1_1_1	EXIST::FUNCTION:
 SSL_CTX_set_record_padding_callback_arg 452	1_1_1	EXIST::FUNCTION:
 SSL_CTX_use_serverinfo_ex               453	1_1_1	EXIST::FUNCTION:
+SSL_early_get1_extensions_present       454	1_1_1	EXIST::FUNCTION: