From 9db5a8f58dd26d547cf530beeb41155d97e700f0 Mon Sep 17 00:00:00 2001
From: Stanislav Malyshev <stas@php.net>
Date: Mon, 20 Jan 2020 21:33:17 -0800
Subject: [PATCH] Fix #79099: OOB read in php_strip_tags_ex

(cherry picked from commit 0f79b1bf301f455967676b5129240140c5c45b09)
---
 ext/standard/string.c                 |  6 ++---
 ext/standard/tests/file/bug79099.phpt | 32 +++++++++++++++++++++++++++
 2 files changed, 35 insertions(+), 3 deletions(-)
 create mode 100644 ext/standard/tests/file/bug79099.phpt

diff --git a/ext/standard/string.c b/ext/standard/string.c
index 569452ca93..9b75adc3b7 100644
--- a/ext/standard/string.c
+++ b/ext/standard/string.c
@@ -4770,7 +4770,7 @@ PHPAPI size_t php_strip_tags_ex(char *rbuf, int len, int *stateptr, char *allow,
 				if (state == 4) {
 					/* Inside <!-- comment --> */
 					break;
-				} else if (state == 2 && *(p-1) != '\\') {
+				} else if (state == 2 && p >= buf + 1 && *(p-1) != '\\') {
 					if (lc == c) {
 						lc = '\0';
 					} else if (lc != '\\') {
@@ -4797,7 +4797,7 @@ PHPAPI size_t php_strip_tags_ex(char *rbuf, int len, int *stateptr, char *allow,
 
 			case '!':
 				/* JavaScript & Other HTML scripting languages */
-				if (state == 1 && *(p-1) == '<') {
+				if (state == 1 && p >= buf + 1 && *(p-1) == '<') {
 					state = 3;
 					lc = c;
 				} else {
@@ -4824,7 +4824,7 @@ PHPAPI size_t php_strip_tags_ex(char *rbuf, int len, int *stateptr, char *allow,
 
 			case '?':
 
-				if (state == 1 && *(p-1) == '<') {
+				if (state == 1 && p >= buf + 1 && *(p-1) == '<') {
 					br=0;
 					state=2;
 					break;
diff --git a/ext/standard/tests/file/bug79099.phpt b/ext/standard/tests/file/bug79099.phpt
new file mode 100644
index 0000000000..7c842f4654
--- /dev/null
+++ b/ext/standard/tests/file/bug79099.phpt
@@ -0,0 +1,32 @@
+--TEST--
+Bug #79099 (OOB read in php_strip_tags_ex)
+--FILE--
+<?php
+$stream = fopen('php://memory', 'w+');
+fputs($stream, "<?\n\"\n");
+rewind($stream);
+var_dump(fgetss($stream));
+var_dump(fgetss($stream));
+fclose($stream);
+
+$stream = fopen('php://memory', 'w+');
+fputs($stream, "<\0\n!\n");
+rewind($stream);
+var_dump(fgetss($stream));
+var_dump(fgetss($stream));
+fclose($stream);
+
+$stream = fopen('php://memory', 'w+');
+fputs($stream, "<\0\n?\n");
+rewind($stream);
+var_dump(fgetss($stream));
+var_dump(fgetss($stream));
+fclose($stream);
+?>
+--EXPECT--
+string(0) ""
+string(0) ""
+string(0) ""
+string(0) ""
+string(0) ""
+string(0) ""