Fix dblink_connect() so that it verifies that a password is supplied in the

conninfo string *before* trying to connect to the remote server, not after.
As pointed out by Marko Kreen, in certain not-very-plausible situations
this could result in sending a password from the postgres user's .pgpass file,
or other places that non-superusers shouldn't have access to, to an
untrustworthy remote server.  The cleanest fix seems to be to expose libpq's
conninfo-string-parsing code so that dblink can check for a password option
without duplicating the parsing logic.

Joe Conway, with a little cleanup by Tom Lane

src/interfaces/libpq/exports.txt

@@ -1,4 +1,4 @@
-# $PostgreSQL: pgsql/src/interfaces/libpq/exports.txt,v 1.21 2008/09/19 20:06:13 tgl Exp $
+# $PostgreSQL: pgsql/src/interfaces/libpq/exports.txt,v 1.22 2008/09/22 13:55:14 tgl Exp $
 # Functions to be exported by libpq DLLs
 PQconnectdb               1
 PQsetdbLogin              2
@@ -151,3 +151,4 @@ PQsetInstanceData         148
 PQresultInstanceData      149
 PQresultSetInstanceData   150
 PQfireResultCreateEvents  151
+PQconninfoParse           152

src/interfaces/libpq/fe-connect.c

@@ -8,7 +8,7 @@
  *
  *
  * IDENTIFICATION
- *	  $PostgreSQL: pgsql/src/interfaces/libpq/fe-connect.c,v 1.360 2008/09/17 04:31:08 tgl Exp $
+ *	  $PostgreSQL: pgsql/src/interfaces/libpq/fe-connect.c,v 1.361 2008/09/22 13:55:14 tgl Exp $
  *
  *-------------------------------------------------------------------------
  */
@@ -232,7 +232,8 @@ static PGconn *makeEmptyPGconn(void);
 static void freePGconn(PGconn *conn);
 static void closePGconn(PGconn *conn);
 static PQconninfoOption *conninfo_parse(const char *conninfo,
-			   PQExpBuffer errorMessage, bool *password_from_string);
+			   PQExpBuffer errorMessage, bool use_defaults,
+			   bool *password_from_string);
 static char *conninfo_getval(PQconninfoOption *connOptions,
 				const char *keyword);
 static void defaultNoticeReceiver(void *arg, const PGresult *res);
@@ -376,7 +377,7 @@ connectOptions1(PGconn *conn, const char *conninfo)
 	/*
 	 * Parse the conninfo string
 	 */
-	connOptions = conninfo_parse(conninfo, &conn->errorMessage,
+	connOptions = conninfo_parse(conninfo, &conn->errorMessage, true,
 								 &conn->pgpass_from_client);
 	if (connOptions == NULL)
 	{
@@ -542,7 +543,9 @@ connectOptions2(PGconn *conn)
  *		PQconndefaults
  *
  * Parse an empty string like PQconnectdb() would do and return the
- * working connection options array.
+ * resulting connection options array, ie, all the default values that are
+ * available from the environment etc.  On error (eg out of memory),
+ * NULL is returned.
  *
  * Using this function, an application may determine all possible options
  * and their current default values.
@@ -561,7 +564,10 @@ PQconndefaults(void)
 	PQconninfoOption *connOptions;
 
 	initPQExpBuffer(&errorBuf);
-	connOptions = conninfo_parse("", &errorBuf, &password_from_string);
+	if (errorBuf.data == NULL)
+		return NULL;			/* out of memory already :-( */
+	connOptions = conninfo_parse("", &errorBuf, true,
+								 &password_from_string);
 	termPQExpBuffer(&errorBuf);
 	return connOptions;
 }
@@ -3102,18 +3108,56 @@ parseServiceInfo(PQconninfoOption *options, PQExpBuffer errorMessage)
 }
 
 
+/*
+ *		PQconninfoParse
+ *
+ * Parse a string like PQconnectdb() would do and return the
+ * resulting connection options array.  NULL is returned on failure.
+ * The result contains only options specified directly in the string,
+ * not any possible default values.
+ *
+ * If errmsg isn't NULL, *errmsg is set to NULL on success, or a malloc'd
+ * string on failure (use PQfreemem to free it).  In out-of-memory conditions
+ * both *errmsg and the result could be NULL.
+ *
+ * NOTE: the returned array is dynamically allocated and should
+ * be freed when no longer needed via PQconninfoFree().
+ */
+PQconninfoOption *
+PQconninfoParse(const char *conninfo, char **errmsg)
+{
+	PQExpBufferData errorBuf;
+	bool		password_from_string;
+	PQconninfoOption *connOptions;
+
+	if (errmsg)
+		*errmsg = NULL;			/* default */
+	initPQExpBuffer(&errorBuf);
+	if (errorBuf.data == NULL)
+		return NULL;			/* out of memory already :-( */
+	connOptions = conninfo_parse(conninfo, &errorBuf, false,
+								 &password_from_string);
+	if (connOptions == NULL && errmsg)
+		*errmsg = errorBuf.data;
+	else
+		termPQExpBuffer(&errorBuf);
+	return connOptions;
+}
+
 /*
  * Conninfo parser routine
  *
  * If successful, a malloc'd PQconninfoOption array is returned.
  * If not successful, NULL is returned and an error message is
  * left in errorMessage.
+ * Defaults are supplied (from a service file, environment variables, etc)
+ * for unspecified options, but only if use_defaults is TRUE.
  * *password_from_string is set TRUE if we got a password from the
  * conninfo string, otherwise FALSE.
  */
 static PQconninfoOption *
 conninfo_parse(const char *conninfo, PQExpBuffer errorMessage,
-			   bool *password_from_string)
+			   bool use_defaults, bool *password_from_string)
 {
 	char	   *pname;
 	char	   *pval;
@@ -3293,6 +3337,12 @@ conninfo_parse(const char *conninfo, PQExpBuffer errorMessage,
 	/* Done with the modifiable input string */
 	free(buf);
 
+	/*
+	 * Stop here if caller doesn't want defaults filled in.
+	 */
+	if (!use_defaults)
+		return options;
+
 	/*
 	 * If there's a service spec, use it to obtain any not-explicitly-given
 	 * parameters.

src/interfaces/libpq/libpq-fe.h

@@ -7,7 +7,7 @@
  * Portions Copyright (c) 1996-2008, PostgreSQL Global Development Group
  * Portions Copyright (c) 1994, Regents of the University of California
  *
- * $PostgreSQL: pgsql/src/interfaces/libpq/libpq-fe.h,v 1.143 2008/09/17 04:31:08 tgl Exp $
+ * $PostgreSQL: pgsql/src/interfaces/libpq/libpq-fe.h,v 1.144 2008/09/22 13:55:14 tgl Exp $
  *
  *-------------------------------------------------------------------------
  */
@@ -164,6 +164,7 @@ typedef struct _PQprintOpt
 
 /* ----------------
  * Structure for the conninfo parameter definitions returned by PQconndefaults
+ * or PQconninfoParse.
  *
  * All fields except "val" point at static strings which must not be altered.
  * "val" is either NULL or a malloc'd current-value string.  PQconninfoFree()
@@ -177,7 +178,7 @@ typedef struct _PQconninfoOption
 	char	   *compiled;		/* Fallback compiled in default value	*/
 	char	   *val;			/* Option's current value, or NULL		 */
 	char	   *label;			/* Label for field in connect dialog	*/
-	char	   *dispchar;		/* Character to display for this field in a
+	char	   *dispchar;		/* Indicates how to display this field in a
 								 * connect dialog. Values are: "" Display
 								 * entered value as is "*" Password field -
 								 * hide value "D"  Debug option - don't show
@@ -243,7 +244,10 @@ extern void PQfinish(PGconn *conn);
 /* get info about connection options known to PQconnectdb */
 extern PQconninfoOption *PQconndefaults(void);
 
-/* free the data structure returned by PQconndefaults() */
+/* parse connection options in same way as PQconnectdb */
+extern PQconninfoOption *PQconninfoParse(const char *conninfo, char **errmsg);
+
+/* free the data structure returned by PQconndefaults() or PQconninfoParse() */
 extern void PQconninfoFree(PQconninfoOption *connOptions);
 
 /*