Fix #76130: Heap Buffer Overflow (READ: 1786) in exif_iif_add_value

The MakerNote is not necessarily null-terminated, so we must not use
`strlen()` to avoid OOB reads.  Instead `php_strnlen()` is the proper
way to handle this.

ext/exif/exif.c

@@ -1710,7 +1710,7 @@ static void exif_iif_add_value(image_info_type *image_info, int section_index, c
 		case TAG_FMT_UNDEFINED:
 			if (value) {
 				if (tag == TAG_MAKER_NOTE) {
-					length = MIN(length, strlen(value));
+					length = (int) php_strnlen(value, length);
 				}
 
 				/* do not recompute length here */

ext/exif/tests/bug76130.phpt

@@ -0,0 +1,20 @@
+--TEST--
+Bug #76130 (Heap Buffer Overflow (READ: 1786) in exif_iif_add_value)
+--DESCRIPTION--
+This test is meant to exhibit memory issues with the `-m` option. Since a lot of
+notices and warnings are to be expected anyway, we suppress these, since the are
+not relevant for this test.
+--INI--
+error_reporting=E_ALL & ~E_WARNING & ~E_NOTICE
+--SKIPIF--
+<?php
+if (!extension_loaded('exif')) die('skip exif extension not available');
+?>
+--FILE--
+<?php
+exif_read_data(__DIR__ . '/bug76130_1.jpg');
+exif_read_data(__DIR__ . '/bug76130_2.jpg');
+?>
+===DONE===
+--EXPECT--
+===DONE===