Remove support for SSL3_FLAGS_DELAY_CLIENT_FINISHED

This flag was not set anywhere within the codebase (only read). It could
only be set by an app reaching directly into s->s3->flags and setting it
directly. However that method became impossible when libssl was opaquified.

Even in 1.0.2/1.0.1 if an app set the flag directly it is only relevant to
ssl3_connect(), which calls SSL_clear() during initialisation that clears
any flag settings. Therefore it could take effect if the app set the flag
after the handshake has started but before it completed. It seems quite
unlikely that any apps really do this (especially as it is completely
undocumented).

The purpose of the flag is suppress flushing of the write bio on the client
side at the end of the handshake after the client has written the Finished
message whilst resuming a session. This enables the client to send
application data as part of the same flight as the Finished message.

This flag also controls the setting of a second flag SSL3_FLAGS_POP_BUFFER.
There is an interesting comment in the code about this second flag in the
implementation of ssl3_write:

	/* This is an experimental flag that sends the
	 * last handshake message in the same packet as the first
	 * use data - used to see if it helps the TCP protocol during
	 * session-id reuse */

It seems the experiment did not work because as far as I can tell nothing
is using this code. The above comment has been in the code since SSLeay.

This commit removes support for SSL3_FLAGS_DELAY_CLIENT_FINISHED, as well
as the associated SSL3_FLAGS_POP_BUFFER.
Reviewed-by: NRich Salz <rsalz@openssl.org>

CHANGES

@@ -3,6 +3,12 @@
  _______________
 
  Changes between 1.0.2 and 1.1.0  [xx XXX xxxx]
+  *) Dropped support for the SSL3_FLAGS_DELAY_CLIENT_FINISHED flag. This SSLeay
+     era flag was never set throughout the codebase (only read). Also removed
+     SSL3_FLAGS_POP_BUFFER which was only used if
+     SSL3_FLAGS_DELAY_CLIENT_FINISHED was also set.
+     [Matt Caswell]
+
   *) Changed the default name options in the "ca", "crl", "req" and "x509"
      to be "oneline" instead of "compat".
      [Richard Levitte]

include/openssl/ssl3.h

@@ -360,10 +360,10 @@ extern "C" {
 # define SSL3_CT_NUMBER                  9
 
 # define SSL3_FLAGS_NO_RENEGOTIATE_CIPHERS       0x0001
-# define SSL3_FLAGS_DELAY_CLIENT_FINISHED        0x0002
-# define SSL3_FLAGS_POP_BUFFER                   0x0004
+
 /* Removed from OpenSSL 1.1.0 */
 # define TLS1_FLAGS_TLS_PADDING_BUG              0x0
+
 # define TLS1_FLAGS_SKIP_CERT_VERIFY             0x0010
 /*
  * Set when the handshake is ready to process peer's ChangeCipherSpec message.

ssl/d1_clnt.c

@@ -604,8 +604,6 @@ int dtls1_connect(SSL *s)
                 goto end;
             s->state = SSL3_ST_CW_FLUSH;
 
-            /* clear flags */
-            s->s3->flags &= ~SSL3_FLAGS_POP_BUFFER;
             if (s->hit) {
                 s->s3->tmp.next_state = SSL_ST_OK;
 #ifndef OPENSSL_NO_SCTP
@@ -614,17 +612,6 @@ int dtls1_connect(SSL *s)
                     s->s3->tmp.next_state = DTLS1_SCTP_ST_CW_WRITE_SOCK;
                 }
 #endif
-                if (s->s3->flags & SSL3_FLAGS_DELAY_CLIENT_FINISHED) {
-                    s->state = SSL_ST_OK;
-#ifndef OPENSSL_NO_SCTP
-                    if (BIO_dgram_is_sctp(SSL_get_wbio(s))) {
-                        s->d1->next_state = SSL_ST_OK;
-                        s->state = DTLS1_SCTP_ST_CW_WRITE_SOCK;
-                    }
-#endif
-                    s->s3->flags |= SSL3_FLAGS_POP_BUFFER;
-                    s->s3->delay_buf_pop_ret = 0;
-                }
             } else {
 #ifndef OPENSSL_NO_SCTP
                 /*
@@ -711,13 +698,8 @@ int dtls1_connect(SSL *s)
             /* clean a few things up */
             ssl3_cleanup_key_block(s);
 
-            /*
-             * If we are not 'joining' the last two packets, remove the
-             * buffering now
-             */
-            if (!(s->s3->flags & SSL3_FLAGS_POP_BUFFER))
-                ssl_free_wbio_buffer(s);
-            /* else do it later in ssl3_write */
+            /* Remove the buffering */
+            ssl_free_wbio_buffer(s);
 
             s->init_num = 0;
             s->renegotiate = 0;

ssl/s3_clnt.c

@@ -518,15 +518,8 @@ int ssl3_connect(SSL *s)
                 goto end;
             s->state = SSL3_ST_CW_FLUSH;
 
-            /* clear flags */
-            s->s3->flags &= ~SSL3_FLAGS_POP_BUFFER;
             if (s->hit) {
                 s->s3->tmp.next_state = SSL_ST_OK;
-                if (s->s3->flags & SSL3_FLAGS_DELAY_CLIENT_FINISHED) {
-                    s->state = SSL_ST_OK;
-                    s->s3->flags |= SSL3_FLAGS_POP_BUFFER;
-                    s->s3->delay_buf_pop_ret = 0;
-                }
             } else {
                 /*
                  * Allow NewSessionTicket if ticket expected
@@ -589,13 +582,8 @@ int ssl3_connect(SSL *s)
             BUF_MEM_free(s->init_buf);
             s->init_buf = NULL;
 
-            /*
-             * If we are not 'joining' the last two packets, remove the
-             * buffering now
-             */
-            if (!(s->s3->flags & SSL3_FLAGS_POP_BUFFER))
-                ssl_free_wbio_buffer(s);
-            /* else do it later in ssl3_write */
+            /* remove the buffering */
+            ssl_free_wbio_buffer(s);
 
             s->init_num = 0;
             s->renegotiate = 0;

ssl/s3_lib.c

@@ -4131,54 +4131,12 @@ int ssl3_shutdown(SSL *s)
 
 int ssl3_write(SSL *s, const void *buf, int len)
 {
-    int ret, n;
-
-#if 0
-    if (s->shutdown & SSL_SEND_SHUTDOWN) {
-        s->rwstate = SSL_NOTHING;
-        return (0);
-    }
-#endif
     clear_sys_error();
     if (s->s3->renegotiate)
         ssl3_renegotiate_check(s);
 
-    /*
-     * This is an experimental flag that sends the last handshake message in
-     * the same packet as the first use data - used to see if it helps the
-     * TCP protocol during session-id reuse
-     */
-    /* The second test is because the buffer may have been removed */
-    if ((s->s3->flags & SSL3_FLAGS_POP_BUFFER) && (s->wbio == s->bbio)) {
-        /* First time through, we write into the buffer */
-        if (s->s3->delay_buf_pop_ret == 0) {
-            ret = ssl3_write_bytes(s, SSL3_RT_APPLICATION_DATA, buf, len);
-            if (ret <= 0)
-                return (ret);
-
-            s->s3->delay_buf_pop_ret = ret;
-        }
-
-        s->rwstate = SSL_WRITING;
-        n = BIO_flush(s->wbio);
-        if (n <= 0)
-            return (n);
-        s->rwstate = SSL_NOTHING;
-
-        /* We have flushed the buffer, so remove it */
-        ssl_free_wbio_buffer(s);
-        s->s3->flags &= ~SSL3_FLAGS_POP_BUFFER;
-
-        ret = s->s3->delay_buf_pop_ret;
-        s->s3->delay_buf_pop_ret = 0;
-    } else {
-        ret = s->method->ssl_write_bytes(s, SSL3_RT_APPLICATION_DATA,
+    return s->method->ssl_write_bytes(s, SSL3_RT_APPLICATION_DATA,
                                          buf, len);
-        if (ret <= 0)
-            return (ret);
-    }
-
-    return (ret);
 }
 
 static int ssl3_read_internal(SSL *s, void *buf, int len, int peek)

ssl/ssl_locl.h

@@ -1184,7 +1184,6 @@ struct ssl_st {
 
 typedef struct ssl3_state_st {
     long flags;
-    int delay_buf_pop_ret;
     int read_mac_secret_size;
     unsigned char read_mac_secret[EVP_MAX_MD_SIZE];
     int write_mac_secret_size;