Fix PQencryptPasswordConn to work with older server versions.

hlinnaka · hlinnaka · commit 20bf7b2b0afc · 2017-05-04T12:28:25.000+03:00
password_encryption was a boolean before version 10, so cope with "on" and
"off".

Also, change the behavior with "plain", to treat it the same as "md5".
We're discussing removing the password_encryption='plain' option from the
server altogether, which will make this the only reasonable choice, but
even if we kept it, it seems best to never send the password in cleartext.
diff --git a/doc/src/sgml/libpq.sgml b/doc/src/sgml/libpq.sgml
@@ -5902,7 +5902,9 @@ char *PQencryptPasswordConn(PGconn *conn, const char *passwd, const char *user,
       are the cleartext password, and the SQL name of the user it is for.
       <parameter>algorithm</> specifies the encryption algorithm
       to use to encrypt the password. Currently supported algorithms are
-      <literal>md5</>, <literal>scram-sha-256</> and <literal>plain</>.
+      <literal>md5</> and <literal>scram-sha-256</> (<literal>on</> and
+      <literal>off</> are also accepted as aliases for <literal>md5</>, for
+      compatibility with older server versions). Note that support for
       <literal>scram-sha-256</> was introduced in <productname>PostgreSQL</>
       version 10, and will not work correctly with older server versions. If
       <parameter>algorithm</> is <symbol>NULL</>, this function will query
diff --git a/src/interfaces/libpq/fe-auth.c b/src/interfaces/libpq/fe-auth.c
@@ -1168,7 +1168,7 @@ PQencryptPasswordConn(PGconn *conn, const char *passwd, const char *user,
 		{
 			PQclear(res);
 			printfPQExpBuffer(&conn->errorMessage,
-							  libpq_gettext("password_encryption value too long\n"));
+					  libpq_gettext("password_encryption value too long\n"));
 			return NULL;
 		}
 		strcpy(algobuf, val);
@@ -1177,8 +1177,19 @@ PQencryptPasswordConn(PGconn *conn, const char *passwd, const char *user,
 		algorithm = algobuf;
 	}
 
-	/* Ok, now we know what algorithm to use */
+	/*
+	 * Also accept "on" and "off" as aliases for "md5", because
+	 * password_encryption was a boolean before PostgreSQL 10.  We refuse to
+	 * send the password in plaintext even if it was "off".
+	 */
+	if (strcmp(algorithm, "on") == 0 ||
+		strcmp(algorithm, "off") == 0 ||
+		strcmp(algorithm, "plain") == 0)
+		algorithm = "md5";
 
+	/*
+	 * Ok, now we know what algorithm to use
+	 */
 	if (strcmp(algorithm, "scram-sha-256") == 0)
 	{
 		crypt_pwd = pg_fe_scram_build_verifier(passwd);
@@ -1195,14 +1206,10 @@ PQencryptPasswordConn(PGconn *conn, const char *passwd, const char *user,
 			}
 		}
 	}
-	else if (strcmp(algorithm, "plain") == 0)
-	{
-		crypt_pwd = strdup(passwd);
-	}
 	else
 	{
 		printfPQExpBuffer(&conn->errorMessage,
-						  libpq_gettext("unknown password encryption algorithm\n"));
+				   libpq_gettext("unknown password encryption algorithm\n"));
 		return NULL;
 	}
 

Original file line number	Diff line number	Diff line change
`@@ -1168,7 +1168,7 @@ PQencryptPasswordConn(PGconn conn, const char passwd, const char *user,`
`1168`	`1168`	`{`
`1169`	`1169`	`PQclear(res);`
`1170`	`1170`	`printfPQExpBuffer(&conn->errorMessage,`
`1171`		`- libpq_gettext("password_encryption value too long\n"));`
	`1171`	`+ libpq_gettext("password_encryption value too long\n"));`
`1172`	`1172`	`return NULL;`
`1173`	`1173`	`}`
`1174`	`1174`	`strcpy(algobuf, val);`
`@@ -1177,8 +1177,19 @@ PQencryptPasswordConn(PGconn conn, const char passwd, const char *user,`
`1177`	`1177`	`algorithm = algobuf;`
`1178`	`1178`	`}`
`1179`	`1179`
`1180`		`- /* Ok, now we know what algorithm to use */`
	`1180`	`+ /*`
	`1181`	`+ * Also accept "on" and "off" as aliases for "md5", because`
	`1182`	`+ * password_encryption was a boolean before PostgreSQL 10. We refuse to`
	`1183`	`+ * send the password in plaintext even if it was "off".`
	`1184`	`+ */`
	`1185`	`+ if (strcmp(algorithm, "on") == 0 \|\|`
	`1186`	`+ strcmp(algorithm, "off") == 0 \|\|`
	`1187`	`+ strcmp(algorithm, "plain") == 0)`
	`1188`	`+ algorithm = "md5";`
`1181`	`1189`
	`1190`	`+ /*`
	`1191`	`+ * Ok, now we know what algorithm to use`
	`1192`	`+ */`
`1182`	`1193`	`if (strcmp(algorithm, "scram-sha-256") == 0)`
`1183`	`1194`	`{`
`1184`	`1195`	`crypt_pwd = pg_fe_scram_build_verifier(passwd);`
`@@ -1195,14 +1206,10 @@ PQencryptPasswordConn(PGconn conn, const char passwd, const char *user,`
`1195`	`1206`	`}`
`1196`	`1207`	`}`
`1197`	`1208`	`}`
`1198`		`- else if (strcmp(algorithm, "plain") == 0)`
`1199`		`- {`
`1200`		`- crypt_pwd = strdup(passwd);`
`1201`		`- }`
`1202`	`1209`	`else`
`1203`	`1210`	`{`
`1204`	`1211`	`printfPQExpBuffer(&conn->errorMessage,`
`1205`		`- libpq_gettext("unknown password encryption algorithm\n"));`
	`1212`	`+ libpq_gettext("unknown password encryption algorithm\n"));`
`1206`	`1213`	`return NULL;`
`1207`	`1214`	`}`
`1208`	`1215`