Implement Maximum Fragment Length TLS extension.

Based on patch from Tomasz Moń:
https://groups.google.com/forum/#!topic/mailing.openssl.dev/fQxXvCg1uQY

Reviewed-by: Matt Caswell <matt@openssl.org>
Reviewed-by: Bernd Edlinger <bernd.edlinger@hotmail.de>
(Merged from https://github.com/openssl/openssl/pull/1008)

1 files changed, 62 insertions, 6 deletions

diff --git a/doc/man3/SSL_CTX_set_split_send_fragment.pod b/doc/man3/SSL_CTX_set_split_send_fragment.pod
index f65540fc28..ef5e7cda35 100644
--- a/doc/man3/SSL_CTX_set_split_send_fragment.pod
+++ b/doc/man3/SSL_CTX_set_split_send_fragment.pod
@@ -5,8 +5,10 @@
 SSL_CTX_set_max_send_fragment, SSL_set_max_send_fragment,
 SSL_CTX_set_split_send_fragment, SSL_set_split_send_fragment,
 SSL_CTX_set_max_pipelines, SSL_set_max_pipelines,
-SSL_CTX_set_default_read_buffer_len, SSL_set_default_read_buffer_len - Control
-fragment sizes and pipelining operations
+SSL_CTX_set_default_read_buffer_len, SSL_set_default_read_buffer_len,
+SSL_CTX_set_tlsext_max_fragment_length,
+SSL_set_tlsext_max_fragment_length,
+SSL_SESSION_get_max_fragment_length - Control fragment size settings and pipelining operations
 
 =head1 SYNOPSIS
 
@@ -24,6 +26,10 @@ fragment sizes and pipelining operations
  void SSL_CTX_set_default_read_buffer_len(SSL_CTX *ctx, size_t len);
  void SSL_set_default_read_buffer_len(SSL *s, size_t len);
 
+ int SSL_CTX_set_tlsext_max_fragment_length(SSL_CTX *ctx, uint8_t mode);
+ int SSL_set_tlsext_max_fragment_length(SSL *ssl, uint8_t mode);
+ uint8_t SSL_SESSION_get_max_fragment_length(SSL_SESSION *session);
+
 =head1 DESCRIPTION
 
 Some engines are able to process multiple simultaneous crypto operations. This
@@ -99,15 +105,62 @@ greater than the default that would have been used anyway. The normal default
 value depends on a number of factors but it will be at least
 SSL3_RT_MAX_PLAIN_LENGTH + SSL3_RT_MAX_ENCRYPTED_OVERHEAD (16704) bytes.
 
+SSL_CTX_set_tlsext_max_fragment_length() sets the default maximum fragment
+length negotiation mode via value B<mode> to B<ctx>.
+This setting affects only SSL instances created after this function is called.
+It affects the client-side as only its side may initiate this extension use.
+
+SSL_set_tlsext_max_fragment_length() sets the maximum fragment length
+negotiation mode via value B<mode> to B<ssl>.
+This setting will be used during a handshake when extensions are exchanged
+between client and server.
+So it only affects SSL sessions created after this function is called.
+It affects the client-side as only its side may initiate this extension use.
+
+SSL_SESSION_get_max_fragment_length() gets the maximum fragment length
+negotiated in B<session>.
+
 =head1 RETURN VALUES
 
 All non-void functions return 1 on success and 0 on failure.
 
 =head1 NOTES
 
-With the exception of SSL_CTX_set_default_read_buffer_len() and
-SSL_set_default_read_buffer_len() all these functions are implemented using
-macros.
+The Maximum Fragment Length extension support is optional on the server side.
+If the server does not support this extension then
+SSL_SESSION_get_max_fragment_length() will return:
+TLSEXT_max_fragment_length_DISABLED.
+
+The following modes are available:
+
+=over 4
+
+=item TLSEXT_max_fragment_length_DISABLED
+
+Disables Maximum Fragment Length Negotiation (default).
+
+=item TLSEXT_max_fragment_length_512
+
+Sets Maximum Fragment Length to 512 bytes.
+
+=item TLSEXT_max_fragment_length_1024
+
+Sets Maximum Fragment Length to 1024.
+
+=item TLSEXT_max_fragment_length_2048
+
+Sets Maximum Fragment Length to 2048.
+
+=item TLSEXT_max_fragment_length_4096
+
+Sets Maximum Fragment Length to 4096.
+
+=back
+
+With the exception of SSL_CTX_set_default_read_buffer_len()
+SSL_set_default_read_buffer_len(), SSL_CTX_set_tlsext_max_fragment_length(),
+SSL_set_tlsext_max_fragment_length() and SSL_SESSION_get_max_fragment_length()
+all these functions are implemented using macros.
 
 =head1 HISTORY
 
@@ -116,13 +169,16 @@ SSL_CTX_set_split_send_fragment(), SSL_set_split_send_fragment(),
 SSL_CTX_set_default_read_buffer_len() and  SSL_set_default_read_buffer_len()
 functions were added in OpenSSL 1.1.0.
 
+SSL_CTX_set_tlsext_max_fragment_length(), SSL_set_tlsext_max_fragment_length()
+and SSL_SESSION_get_max_fragment_length() were added in OpenSSL 1.1.1.
+
 =head1 SEE ALSO
 
 L<SSL_CTX_set_read_ahead(3)>, L<SSL_pending(3)>
 
 =head1 COPYRIGHT
 
-Copyright 2016 The OpenSSL Project Authors. All Rights Reserved.
+Copyright 2016-2017 The OpenSSL Project Authors. All Rights Reserved.
 
 Licensed under the OpenSSL license (the "License").  You may not use
 this file except in compliance with the License.  You can obtain a copy