Remove ssl renegotiation support.

anarazel · anarazel · commit 426746b93093 · 2015-07-28T22:06:31.000+02:00
While postgres' use of SSL renegotiation is a good idea in theory, it
turned out to not work well in practice. The specification and openssl's
implementation of it have lead to several security issues. Postgres' use
of renegotiation also had its share of bugs.

Additionally OpenSSL has a bunch of bugs around renegotiation, reported
and open for years, that regularly lead to connections breaking with
obscure error messages. We tried increasingly complex workarounds to get
around these bugs, but we didn't find anything complete.

Since these connection breakages often lead to hard to debug problems,
e.g. spuriously failing base backups and significant latency spikes when
synchronous replication is used, we have decided to change the default
setting for ssl renegotiation to 0 (disabled) in the released
backbranches and remove it entirely in 9.5 and master.

Author: Andres Freund
Discussion: 20150624144148.GQ4797@alap3.anarazel.de
Backpatch: 9.5 and master, 9.0-9.4 get a different patch
diff --git a/doc/src/sgml/config.sgml b/doc/src/sgml/config.sgml
@@ -1034,35 +1034,6 @@ include_dir 'conf.d'
       </listitem>
      </varlistentry>
 
-     <varlistentry id="guc-ssl-renegotiation-limit" xreflabel="ssl_renegotiation_limit">
-      <term><varname>ssl_renegotiation_limit</varname> (<type>integer</type>)
-      <indexterm>
-       <primary><varname>ssl_renegotiation_limit</> configuration parameter</primary>
-      </indexterm>
-      </term>
-      <listitem>
-       <para>
-        Specifies how much data can flow over an <acronym>SSL</>-encrypted
-        connection before renegotiation of the session keys will take
-        place. Renegotiation decreases an attacker's chances of doing
-        cryptanalysis when large amounts of traffic can be examined, but it
-        also carries a large performance penalty. The sum of sent and received
-        traffic is used to check the limit. If this parameter is set to 0,
-        renegotiation is disabled. The default is <literal>512MB</>.
-       </para>
-       <note>
-        <para>
-         SSL libraries from before November 2009 are insecure when using SSL
-         renegotiation, due to a vulnerability in the SSL protocol. As a
-         stop-gap fix for this vulnerability, some vendors shipped SSL
-         libraries incapable of doing renegotiation. If any such libraries
-         are in use on the client or server, SSL renegotiation should be
-         disabled.
-        </para>
-       </note>
-      </listitem>
-     </varlistentry>
-
      <varlistentry id="guc-ssl-ciphers" xreflabel="ssl_ciphers">
       <term><varname>ssl_ciphers</varname> (<type>string</type>)
       <indexterm>
diff --git a/src/backend/libpq/be-secure-openssl.c b/src/backend/libpq/be-secure-openssl.c
@@ -16,12 +16,8 @@
  *	  backend can restart automatically, it is important that
  *	  we select an algorithm that continues to provide confidentiality
  *	  even if the attacker has the server's private key.  Ephemeral
- *	  DH (EDH) keys provide this, and in fact provide Perfect Forward
- *	  Secrecy (PFS) except for situations where the session can
- *	  be hijacked during a periodic handshake/renegotiation.
- *	  Even that backdoor can be closed if client certificates
- *	  are used (since the imposter will be unable to successfully
- *	  complete renegotiation).
+ *	  DH (EDH) keys provide this and more (Perfect Forward Secrecy
+ *	  aka PFS).
  *
  *	  N.B., the static private key should still be protected to
  *	  the largest extent possible, to minimize the risk of
@@ -37,12 +33,6 @@
  *	  session.  In this case you'll need to temporarily disable
  *	  EDH by commenting out the callback.
  *
- *	  ...
- *
- *	  Because the risk of cryptanalysis increases as large
- *	  amounts of data are sent with the same session key, the
- *	  session keys are periodically renegotiated.
- *
  *-------------------------------------------------------------------------
  */
 
@@ -92,9 +82,6 @@ static const char *SSLerrmessage(void);
 
 static char *X509_NAME_to_cstring(X509_NAME *name);
 
-/* are we in the middle of a renegotiation? */
-static bool in_ssl_renegotiation = false;
-
 static SSL_CTX *SSL_context = NULL;
 
 /* ------------------------------------------------------------ */
@@ -570,37 +557,6 @@ be_tls_write(Port *port, void *ptr, size_t len, int *waitfor)
 	ssize_t		n;
 	int			err;
 
-	/*
-	 * If SSL renegotiations are enabled and we're getting close to the limit,
-	 * start one now; but avoid it if there's one already in progress.
-	 * Request the renegotiation 1kB before the limit has actually expired.
-	 */
-	if (ssl_renegotiation_limit && !in_ssl_renegotiation &&
-		port->count > (ssl_renegotiation_limit - 1) * 1024L)
-	{
-		in_ssl_renegotiation = true;
-
-		/*
-		 * The way we determine that a renegotiation has completed is by
-		 * observing OpenSSL's internal renegotiation counter.  Make sure we
-		 * start out at zero, and assume that the renegotiation is complete
-		 * when the counter advances.
-		 *
-		 * OpenSSL provides SSL_renegotiation_pending(), but this doesn't seem
-		 * to work in testing.
-		 */
-		SSL_clear_num_renegotiations(port->ssl);
-
-		/* without this, renegotiation fails when a client cert is used */
-		SSL_set_session_id_context(port->ssl, (void *) &SSL_context,
-								   sizeof(SSL_context));
-
-		if (SSL_renegotiate(port->ssl) <= 0)
-			ereport(COMMERROR,
-					(errcode(ERRCODE_PROTOCOL_VIOLATION),
-					 errmsg("SSL failure during renegotiation start")));
-	}
-
 	errno = 0;
 	n = SSL_write(port->ssl, ptr, len);
 	err = SSL_get_error(port->ssl, n);
@@ -646,28 +602,6 @@ be_tls_write(Port *port, void *ptr, size_t len, int *waitfor)
 			break;
 	}
 
-	if (n >= 0)
-	{
-		/* is renegotiation complete? */
-		if (in_ssl_renegotiation &&
-			SSL_num_renegotiations(port->ssl) >= 1)
-		{
-			in_ssl_renegotiation = false;
-			port->count = 0;
-		}
-
-		/*
-		 * if renegotiation is still ongoing, and we've gone beyond the limit,
-		 * kill the connection now -- continuing to use it can be considered a
-		 * security problem.
-		 */
-		if (in_ssl_renegotiation &&
-			port->count > ssl_renegotiation_limit * 1024L)
-			ereport(FATAL,
-					(errcode(ERRCODE_PROTOCOL_VIOLATION),
-					 errmsg("SSL failed to renegotiate connection before limit expired")));
-	}
-
 	return n;
 }
 
diff --git a/src/backend/libpq/be-secure.c b/src/backend/libpq/be-secure.c
@@ -43,13 +43,6 @@ char	   *ssl_key_file;
 char	   *ssl_ca_file;
 char	   *ssl_crl_file;
 
-/*
- *	How much data can be sent across a secure connection
- *	(total in both directions) before we require renegotiation.
- *	Set to 0 to disable renegotiation completely.
- */
-int			ssl_renegotiation_limit;
-
 #ifdef USE_SSL
 bool		ssl_loaded_verify_locations = false;
 #endif
diff --git a/src/backend/utils/misc/guc.c b/src/backend/utils/misc/guc.c
@@ -2577,17 +2577,6 @@ static struct config_int ConfigureNamesInt[] =
 		NULL, assign_tcp_keepalives_interval, show_tcp_keepalives_interval
 	},
 
-	{
-		{"ssl_renegotiation_limit", PGC_USERSET, CONN_AUTH_SECURITY,
-			gettext_noop("Set the amount of traffic to send and receive before renegotiating the encryption keys."),
-			NULL,
-			GUC_UNIT_KB,
-		},
-		&ssl_renegotiation_limit,
-		512 * 1024, 0, MAX_KILOBYTES,
-		NULL, NULL, NULL
-	},
-
 	{
 		{"tcp_keepalives_count", PGC_USERSET, CLIENT_CONN_OTHER,
 			gettext_noop("Maximum number of TCP keepalive retransmits."),
diff --git a/src/backend/utils/misc/postgresql.conf.sample b/src/backend/utils/misc/postgresql.conf.sample
@@ -83,7 +83,6 @@
 					# (change requires restart)
 #ssl_prefer_server_ciphers = on		# (change requires restart)
 #ssl_ecdh_curve = 'prime256v1'		# (change requires restart)
-#ssl_renegotiation_limit = 512MB	# amount of data between renegotiations
 #ssl_cert_file = 'server.crt'		# (change requires restart)
 #ssl_key_file = 'server.key'		# (change requires restart)
 #ssl_ca_file = ''			# (change requires restart)
diff --git a/src/include/libpq/libpq-be.h b/src/include/libpq/libpq-be.h
@@ -92,11 +92,6 @@ typedef struct
 } pg_gssinfo;
 #endif
 
-/*
- * SSL renegotiations
- */
-extern int	ssl_renegotiation_limit;
-
 /*
  * This is used by the postmaster in its communication with frontends.  It
  * contains all state information needed during this communication before the
