From 82f1bf1b6bc3a43aba62214870e6d0931e93a6d9 Mon Sep 17 00:00:00 2001
From: "Christoph M. Becker" <cmbecker69@gmx.de>
Date: Mon, 31 Jan 2022 15:43:24 +0100
Subject: [PATCH] Fix #81708: UAF due to php_filter_float() failing for ints

We must only release the zval, if we actually assign a new zval.
---
 ext/filter/logical_filters.c   |  2 +-
 ext/filter/tests/bug81708.phpt | 20 ++++++++++++++++++++
 2 files changed, 21 insertions(+), 1 deletion(-)
 create mode 100644 ext/filter/tests/bug81708.phpt

diff --git a/ext/filter/logical_filters.c b/ext/filter/logical_filters.c
index 1bf7c00d13c6..95f7a99e34b1 100644
--- a/ext/filter/logical_filters.c
+++ b/ext/filter/logical_filters.c
@@ -436,10 +436,10 @@ void php_filter_float(PHP_INPUT_FILTER_PARAM_DECL) /* {{{ */
 
 	switch (is_numeric_string(num, p - num, &lval, &dval, 0)) {
 		case IS_LONG:
-			zval_ptr_dtor(value);
 			if ((min_range_set && (lval < min_range)) || (max_range_set && (lval > max_range))) {
 				goto error;
 			}
+			zval_ptr_dtor(value);
 			ZVAL_DOUBLE(value, (double)lval);
 			break;
 		case IS_DOUBLE:
diff --git a/ext/filter/tests/bug81708.phpt b/ext/filter/tests/bug81708.phpt
new file mode 100644
index 000000000000..d0036af13682
--- /dev/null
+++ b/ext/filter/tests/bug81708.phpt
@@ -0,0 +1,20 @@
+--TEST--
+Bug #81708 (UAF due to php_filter_float() failing for ints)
+--SKIPIF--
+<?php
+if (!extension_loaded("filter")) die("skip filter extension not available");
+?>
+--INI--
+opcache.enable_cli=0
+--FILE--
+<?php
+$input = "+" . str_repeat("1", 2); // avoid string interning
+filter_var(
+    $input,
+    FILTER_VALIDATE_FLOAT,
+    ["options" => ['min_range' => -1, 'max_range' => 1]]
+);
+var_dump($input);
+?>
+--EXPECT--
+string(3) "+11"