Fix GH-16812: UAF on readline_info() after readline_write_history() call.

close GH-16813

Author: devnexen

NEWS

@@ -24,6 +24,9 @@ PHP                                                                        NEWS
 - PDO:
   . Fixed memory leak of `setFetchMode()`. (SakiTakamachi)
 
+- Readline:
+  . Fixed UAF with readline_info(). (David Carlier)
+
 - Reflection:
   . Fixed the name of the second parameter of
     ReflectionClass::resetAsLazyGhost(). (Arnaud)

ext/readline/readline.c

@@ -181,7 +181,7 @@ PHP_FUNCTION(readline_info)
 		add_assoc_long(return_value,"attempted_completion_over",rl_attempted_completion_over);
 	} else {
 		if (zend_string_equals_literal_ci(what,"line_buffer")) {
-			oldstr = rl_line_buffer;
+			oldstr = strdup(rl_line_buffer ? rl_line_buffer : "");
 			if (value) {
 				if (!try_convert_to_string(value)) {
 					RETURN_THROWS();
@@ -191,7 +191,8 @@ PHP_FUNCTION(readline_info)
 					rl_line_buffer = malloc(Z_STRLEN_P(value) + 1);
 				} else if (strlen(oldstr) < Z_STRLEN_P(value)) {
 					rl_extend_line_buffer(Z_STRLEN_P(value) + 1);
-					oldstr = rl_line_buffer;
+					free(oldstr);
+					oldstr = strdup(rl_line_buffer ? rl_line_buffer : "");
 				}
 				memcpy(rl_line_buffer, Z_STRVAL_P(value), Z_STRLEN_P(value) + 1);
 #else
@@ -208,6 +209,7 @@ PHP_FUNCTION(readline_info)
 #endif
 			}
 			RETVAL_STRING(SAFE_STRING(oldstr));
+			free(oldstr);
 		} else if (zend_string_equals_literal_ci(what, "point")) {
 			RETVAL_LONG(rl_point);
 #ifndef PHP_WIN32

ext/readline/tests/gh16812.phpt

@@ -0,0 +1,15 @@
+--TEST--
+GH-16812 readline_info(): UAF
+--EXTENSIONS--
+readline
+--SKIPIF--
+<?php
+if (getenv('SKIP_REPEAT')) die("skip readline has global state");
+?>
+--FILE--
+<?php
+readline_write_history(NULL);
+var_dump(readline_info('line_buffer', 'test'));
+?>
+--EXPECT--
+string(0) ""