Add a new GUC parameter backslash_quote, which determines whether the SQL

parser will allow "\'" to be used to represent a literal quote mark.  The
"\'" representation has been deprecated for some time in favor of the
SQL-standard representation "''" (two single quote marks), but it has been
used often enough that just disallowing it immediately won't do.  Hence
backslash_quote allows the settings "on", "off", and "safe_encoding",
the last meaning to allow "\'" only if client_encoding is a valid server
encoding.  That is now the default, and the reason is that in encodings
such as SJIS that allow 0x5c (ASCII backslash) to be the last byte of a
multibyte character, accepting "\'" allows SQL-injection attacks as per
CVE-2006-2314 (further details will be published after release).  The
"on" setting is available for backward compatibility, but it must not be
used with clients that are exposed to untrusted input.

Thanks to Akio Ishida and Yasuo Ohgaki for identifying this security issue.

doc/src/sgml/config.sgml

@@ -1,5 +1,5 @@
 <!--
-$PostgreSQL: pgsql/doc/src/sgml/config.sgml,v 1.36.2.5 2006/04/18 12:41:29 momjian Exp $
+$PostgreSQL: pgsql/doc/src/sgml/config.sgml,v 1.36.2.6 2006/05/21 20:11:02 tgl Exp $
 -->
 <chapter Id="runtime-config">
   <title>Server Configuration</title>
@@ -3660,6 +3660,35 @@ dynamic_library_path = 'C:\tools\postgresql;H:\my_project\lib;$libdir'
       </listitem>
      </varlistentry>
 
+     <varlistentry id="guc-backslash-quote" xreflabel="backslash_quote">
+      <term><varname>backslash_quote</varname> (<type>string</type>)</term>
+      <indexterm><primary>strings</><secondary>backslash quotes</></>
+      <indexterm>
+       <primary><varname>backslash_quote</> configuration parameter</primary>
+      </indexterm>
+      <listitem>
+       <para>
+        This controls whether a quote mark can be represented by
+        <literal>\'</> in a string literal.  The preferred, SQL-standard way
+        to represent a quote mark is by doubling it (<literal>''</>) but
+        <productname>PostgreSQL</> has historically also accepted
+        <literal>\'</>. However, use of <literal>\'</> creates security risks
+        because in some client character set encodings, there are multibyte
+        characters in which the last byte is numerically equivalent to ASCII
+        <literal>\</>.  If client-side code does escaping incorrectly then a
+        SQL-injection attack is possible.  This risk can be prevented by
+        making the server reject queries in which a quote mark appears to be
+        escaped by a backslash.
+        The allowed values of <varname>backslash_quote</> are
+        <literal>on</> (allow <literal>\'</> always),
+        <literal>off</> (reject always), and
+        <literal>safe_encoding</> (allow only if client encoding does not
+        allow ASCII <literal>\</> within a multibyte character).
+        <literal>safe_encoding</> is the default setting.
+       </para>
+      </listitem>
+     </varlistentry>
+
      <varlistentry id="guc-default-with-oids" xreflabel="default_with_oids">
       <term><varname>default_with_oids</varname> (<type>boolean</type>)</term>
       <indexterm>

src/backend/parser/scan.l

@@ -24,7 +24,7 @@
  * Portions Copyright (c) 1994, Regents of the University of California
  *
  * IDENTIFICATION
- *	  $PostgreSQL: pgsql/src/backend/parser/scan.l,v 1.128 2005/08/16 00:48:12 tgl Exp $
+ *	  $PostgreSQL: pgsql/src/backend/parser/scan.l,v 1.128.2.1 2006/05/21 20:11:02 tgl Exp $
  *
  *-------------------------------------------------------------------------
  */
@@ -51,13 +51,14 @@ static int		xcdepth = 0;	/* depth of nesting in slash-star comments */
 static char    *dolqstart;      /* current $foo$ quote start string */
 
 /*
- * GUC variable.  This is a DIRECT violation of the warning given at the
+ * GUC variables.  This is a DIRECT violation of the warning given at the
  * head of gram.y, ie flex/bison code must not depend on any GUC variables;
- * as such, changing its value can induce very unintuitive behavior.
+ * as such, changing their values can induce very unintuitive behavior.
  * But we shall have to live with it as a short-term thing until the switch
  * to SQL-standard string syntax is complete.
  */
-bool			escape_string_warning;
+BackslashQuoteType backslash_quote = BACKSLASH_QUOTE_SAFE_ENCODING;
+bool			escape_string_warning = true;
 
 static bool		warn_on_first_escape;
 
@@ -453,6 +454,14 @@ other			.
 <xq>{xqescape}  {
 					if (yytext[1] == '\'')
 					{
+						if (backslash_quote == BACKSLASH_QUOTE_OFF ||
+							(backslash_quote == BACKSLASH_QUOTE_SAFE_ENCODING &&
+							 PG_ENCODING_IS_CLIENT_ONLY(pg_get_client_encoding())))
+							ereport(ERROR,
+									(errcode(ERRCODE_NONSTANDARD_USE_OF_ESCAPE_CHARACTER),
+									 errmsg("unsafe use of \\' in a string literal"),
+									 errhint("Use '' to write quotes in strings. \\' is insecure in client-only encodings."),
+									 errposition(pg_err_position())));
 						if (warn_on_first_escape && escape_string_warning)
 							ereport(WARNING,
 									(errcode(ERRCODE_NONSTANDARD_USE_OF_ESCAPE_CHARACTER),

src/backend/utils/misc/guc.c

@@ -10,7 +10,7 @@
  * Written by Peter Eisentraut <peter_e@gmx.net>.
  *
  * IDENTIFICATION
- *	  $PostgreSQL: pgsql/src/backend/utils/misc/guc.c,v 1.299.2.2 2006/02/12 22:32:57 tgl Exp $
+ *	  $PostgreSQL: pgsql/src/backend/utils/misc/guc.c,v 1.299.2.3 2006/05/21 20:11:02 tgl Exp $
  *
  *--------------------------------------------------------------------
  */
@@ -46,6 +46,7 @@
 #include "optimizer/geqo.h"
 #include "optimizer/paths.h"
 #include "optimizer/prep.h"
+#include "parser/gramparse.h"
 #include "parser/parse_expr.h"
 #include "parser/parse_relation.h"
 #include "parser/scansup.h"
@@ -135,6 +136,7 @@ static bool assign_stage_log_stats(bool newval, bool doit, GucSource source);
 static bool assign_log_stats(bool newval, bool doit, GucSource source);
 static bool assign_transaction_read_only(bool newval, bool doit, GucSource source);
 static const char *assign_canonical_path(const char *newval, bool doit, GucSource source);
+static const char *assign_backslash_quote(const char *newval, bool doit, GucSource source);
 
 static bool assign_tcp_keepalives_idle(int newval, bool doit, GucSource source);
 static bool assign_tcp_keepalives_interval(int newval, bool doit, GucSource source);
@@ -203,6 +205,7 @@ static char *syslog_ident_str;
 static bool phony_autocommit;
 static bool session_auth_is_superuser;
 static double phony_random_seed;
+static char *backslash_quote_string;
 static char *client_encoding_string;
 static char *datestyle_string;
 static char *default_iso_level_string;
@@ -1659,6 +1662,15 @@ static struct config_string ConfigureNamesString[] =
 		"", NULL, NULL
 	},
 
+	{
+		{"backslash_quote", PGC_USERSET, COMPAT_OPTIONS_PREVIOUS,
+			gettext_noop("Sets whether \"\\'\" is allowed in string literals."),
+			gettext_noop("Valid values are ON, OFF, and SAFE_ENCODING.")
+		},
+		&backslash_quote_string,
+		"safe_encoding", assign_backslash_quote, NULL
+	},
+
 	{
 		{"client_encoding", PGC_USERSET, CLIENT_CONN_LOCALE,
 			gettext_noop("Sets the client's character set encoding."),
@@ -5930,6 +5942,32 @@ assign_canonical_path(const char *newval, bool doit, GucSource source)
 		return newval;
 }
 
+static const char *
+assign_backslash_quote(const char *newval, bool doit, GucSource source)
+{
+	BackslashQuoteType bq;
+	bool	bqbool;
+
+	/*
+	 * Although only "on", "off", and "safe_encoding" are documented,
+	 * we use parse_bool so we can accept all the likely variants of
+	 * "on" and "off".
+	 */
+	if (pg_strcasecmp(newval, "safe_encoding") == 0)
+		bq = BACKSLASH_QUOTE_SAFE_ENCODING;
+	else if (parse_bool(newval, &bqbool))
+	{
+		bq = bqbool ? BACKSLASH_QUOTE_ON : BACKSLASH_QUOTE_OFF;
+	}
+	else
+		return NULL;			/* reject */
+
+	if (doit)
+		backslash_quote = bq;
+
+	return newval;
+}
+
 static bool
 assign_tcp_keepalives_idle(int newval, bool doit, GucSource source)
 {

src/backend/utils/misc/postgresql.conf.sample

@@ -413,10 +413,11 @@
 # - Previous Postgres Versions -
 
 #add_missing_from = off
-#regex_flavor = advanced		# advanced, extended, or basic
+#backslash_quote = safe_encoding	# on, off, or safe_encoding
-#sql_inheritance = on
 #default_with_oids = off
 #escape_string_warning = off
+#regex_flavor = advanced		# advanced, extended, or basic
+#sql_inheritance = on
 
 # - Other Platforms & Clients -
 

src/include/parser/gramparse.h

@@ -7,7 +7,7 @@
  * Portions Copyright (c) 1996-2005, PostgreSQL Global Development Group
  * Portions Copyright (c) 1994, Regents of the University of California
  *
- * $PostgreSQL: pgsql/src/include/parser/gramparse.h,v 1.31 2004/12/31 22:03:38 pgsql Exp $
+ * $PostgreSQL: pgsql/src/include/parser/gramparse.h,v 1.31.6.1 2006/05/21 20:11:02 tgl Exp $
  *
  *-------------------------------------------------------------------------
  */
@@ -18,6 +18,18 @@
 #include "nodes/parsenodes.h"
 
 
+typedef enum
+{
+	BACKSLASH_QUOTE_OFF,
+	BACKSLASH_QUOTE_ON,
+	BACKSLASH_QUOTE_SAFE_ENCODING
+} BackslashQuoteType;
+
+/* GUC variables in scan.l (every one of these is a bad idea :-() */
+extern BackslashQuoteType backslash_quote;
+extern bool escape_string_warning;
+
+
 /* from parser.c */
 extern int	yylex(void);
 

src/include/utils/guc.h

@@ -7,7 +7,7 @@
  * Copyright (c) 2000-2005, PostgreSQL Global Development Group
  * Written by Peter Eisentraut <peter_e@gmx.net>.
  *
- * $PostgreSQL: pgsql/src/include/utils/guc.h,v 1.63 2005/10/15 02:49:46 momjian Exp $
+ * $PostgreSQL: pgsql/src/include/utils/guc.h,v 1.63.2.1 2006/05/21 20:11:02 tgl Exp $
  *--------------------------------------------------------------------
  */
 #ifndef GUC_H
@@ -120,7 +120,6 @@ extern bool SQL_inheritance;
 extern bool Australian_timezones;
 
 extern bool default_with_oids;
-extern bool escape_string_warning;
 
 extern int	log_min_error_statement;
 extern int	log_min_messages;