From e3bdb2d92600ed45bd46aaf48309a436a9628218 Mon Sep 17 00:00:00 2001
From: Peter Eisentraut <peter_e@gmx.net>
Date: Sat, 17 Mar 2018 08:56:50 -0400
Subject: [PATCH] Set libpq sslcompression to off by default

Since SSL compression is no longer recommended, turn the default in
libpq from on to off.

OpenSSL 1.1.0 and many distribution packages already turn compression
off by default, so such a server won't accept compression anyway.  So
this will mainly affect users of older OpenSSL installations.

Also update the documentation to make clear that this setting is no
longer recommended.

Discussion: https://www.postgresql.org/message-id/flat/595cf3b1-4ffe-7f05-6f72-f72b7afa7993%402ndquadrant.com
---
 doc/src/sgml/libpq.sgml                  | 31 +++++++++++++++---------
 src/interfaces/libpq/fe-connect.c        |  2 +-
 src/interfaces/libpq/fe-secure-openssl.c |  8 +++---
 3 files changed, 25 insertions(+), 16 deletions(-)

diff --git a/doc/src/sgml/libpq.sgml b/doc/src/sgml/libpq.sgml
index da9421486b..1fd5dd9fca 100644
--- a/doc/src/sgml/libpq.sgml
+++ b/doc/src/sgml/libpq.sgml
@@ -1438,19 +1438,28 @@ postgresql://%2Fvar%2Flib%2Fpostgresql/dbname
       <term><literal>sslcompression</literal></term>
       <listitem>
        <para>
-        If set to 1 (default), data sent over SSL connections will be
-        compressed.
-        If set to 0, compression will be disabled (this requires
-        <productname>OpenSSL</productname> 1.0.0 or later).
-        This parameter is ignored if a connection without SSL is made,
-        or if the version of <productname>OpenSSL</productname> used does not support
-        it.
+        If set to 1, data sent over SSL connections will be compressed.  If
+        set to 0, compression will be disabled.  The default is 0.  This
+        parameter is ignored if a connection without SSL is made.
        </para>
+
        <para>
-        Compression uses CPU time, but can improve throughput if
-        the network is the bottleneck.
-        Disabling compression can improve response time and throughput
-        if CPU performance is the limiting factor.
+        SSL compression is nowadays considered insecure and its use is no
+        longer recommended.  <productname>OpenSSL</productname> 1.1.0 disables
+        compression by default, and many operating system distributions
+        disable it in prior versions as well, so setting this parameter to on
+        will not have any effect if the server does not accept compression.
+        On the other hand, <productname>OpenSSL</productname> before 1.0.0
+        does not support disabling compression, so this parameter is ignored
+        with those versions, and whether compression is used depends on the
+        server.
+       </para>
+
+       <para>
+        If security is not a primary concern, compression can improve
+        throughput if the network is the bottleneck.  Disabling compression
+        can improve response time and throughput if CPU performance is the
+        limiting factor.
        </para>
       </listitem>
      </varlistentry>
diff --git a/src/interfaces/libpq/fe-connect.c b/src/interfaces/libpq/fe-connect.c
index 77eebb0ba1..39c19998c2 100644
--- a/src/interfaces/libpq/fe-connect.c
+++ b/src/interfaces/libpq/fe-connect.c
@@ -279,7 +279,7 @@ static const internalPQconninfoOption PQconninfoOptions[] = {
 		"SSL-Mode", "", 12,		/* sizeof("verify-full") == 12 */
 	offsetof(struct pg_conn, sslmode)},
 
-	{"sslcompression", "PGSSLCOMPRESSION", "1", NULL,
+	{"sslcompression", "PGSSLCOMPRESSION", "0", NULL,
 		"SSL-Compression", "", 1,
 	offsetof(struct pg_conn, sslcompression)},
 
diff --git a/src/interfaces/libpq/fe-secure-openssl.c b/src/interfaces/libpq/fe-secure-openssl.c
index 127122563c..1a35b30dbc 100644
--- a/src/interfaces/libpq/fe-secure-openssl.c
+++ b/src/interfaces/libpq/fe-secure-openssl.c
@@ -1188,14 +1188,14 @@ initialize_SSL(PGconn *conn)
 		SSL_set_verify(conn->ssl, SSL_VERIFY_PEER, verify_cb);
 
 	/*
-	 * If the OpenSSL version used supports it (from 1.0.0 on) and the user
-	 * requested it, disable SSL compression.
+	 * Set compression option if the OpenSSL version used supports it (from
+	 * 1.0.0 on).
 	 */
 #ifdef SSL_OP_NO_COMPRESSION
 	if (conn->sslcompression && conn->sslcompression[0] == '0')
-	{
 		SSL_set_options(conn->ssl, SSL_OP_NO_COMPRESSION);
-	}
+	else
+		SSL_clear_options(conn->ssl, SSL_OP_NO_COMPRESSION);
 #endif
 
 	return 0;