Fix bug #78069 - Out-of-bounds read in iconv.c:_php_iconv_mime_decode() due to integer overflow

Author: smalyshev

ext/iconv/iconv.c

@@ -1673,7 +1673,9 @@ static php_iconv_err_t _php_iconv_mime_decode(smart_str *pretval, const char *st
 							 * we can do at this point. */
 							if (*(p1 + 1) == '=') {
 								++p1;
-								--str_left;
+								if (str_left > 1) {
+									--str_left;
+								}
 							}
 
 							err = _php_iconv_appendl(pretval, encoded_word, (size_t)((p1 + 1) - encoded_word), cd_pl);

ext/iconv/tests/bug78069.data

@@ -0,0 +1,15 @@
+--TEST--
+Bug #78069 (Out-of-bounds read in iconv.c:_php_iconv_mime_decode() due to integer overflow)
+--SKIPIF--
+<?php
+if (!extension_loaded('iconv')) die('skip ext/iconv required');
+?>
+--FILE--
+<?php
+$hdr = iconv_mime_decode_headers(file_get_contents(__DIR__ . "/bug78069.data"),2);
+var_dump(count($hdr));
+?>
+DONE
+--EXPECT--
+int(1)
+DONE