From d50532be91f054ef9beb1afca2ea94f4a70f7c4d Mon Sep 17 00:00:00 2001
From: "Christoph M. Becker" <cmbecker69@gmx.de>
Date: Tue, 18 Oct 2022 12:13:16 +0200
Subject: [PATCH] Fix #81739: OOB read due to insufficient validation in
 imageloadfont()

If we swap the byte order of the relevant header bytes, we need to make
sure again that the following multiplication does not overflow.
---
 ext/gd/gd.c                |  7 +++++++
 ext/gd/tests/bug81739.phpt | 24 ++++++++++++++++++++++++
 2 files changed, 31 insertions(+)
 create mode 100644 ext/gd/tests/bug81739.phpt

diff --git a/ext/gd/gd.c b/ext/gd/gd.c
index 336a73969267..fde93bba496f 100644
--- a/ext/gd/gd.c
+++ b/ext/gd/gd.c
@@ -1485,6 +1485,12 @@ PHP_FUNCTION(imageloadfont)
 		font->w = FLIPWORD(font->w);
 		font->h = FLIPWORD(font->h);
 		font->nchars = FLIPWORD(font->nchars);
+		if (overflow2(font->nchars, font->h) || overflow2(font->nchars * font->h, font->w )) {
+			php_error_docref(NULL, E_WARNING, "Error reading font, invalid font header");
+			efree(font);
+			php_stream_close(stream);
+			RETURN_FALSE;
+		}
 		body_size = font->w * font->h * font->nchars;
 	}
 
@@ -1495,6 +1501,7 @@ PHP_FUNCTION(imageloadfont)
 		RETURN_FALSE;
 	}
 
+	ZEND_ASSERT(body_size > 0);
 	font->data = emalloc(body_size);
 	b = 0;
 	while (b < body_size && (n = php_stream_read(stream, &font->data[b], body_size - b)) > 0) {
diff --git a/ext/gd/tests/bug81739.phpt b/ext/gd/tests/bug81739.phpt
new file mode 100644
index 000000000000..cc2a90381bab
--- /dev/null
+++ b/ext/gd/tests/bug81739.phpt
@@ -0,0 +1,24 @@
+--TEST--
+Bug #81739 (OOB read due to insufficient validation in imageloadfont())
+--SKIPIF--
+<?php
+if (!extension_loaded("gd")) die("skip gd extension not available");
+?>
+--FILE--
+<?php
+$s = fopen(__DIR__ . "/font.font", "w");
+// header without character data
+fwrite($s, "\x01\x00\x00\x00\x20\x00\x00\x00\x08\x00\x00\x00\x08\x00\x00\x00");
+fclose($s);
+var_dump(imageloadfont(__DIR__ . "/font.font"));
+?>
+--CLEAN--
+<?php
+@unlink(__DIR__ . "/font.font");
+?>
+--EXPECTF--
+Warning: imageloadfont(): %croduct of memory allocation multiplication would exceed INT_MAX, failing operation gracefully
+ in %s on line %d
+
+Warning: imageloadfont(): Error reading font, invalid font header in %s on line %d
+bool(false)
\ No newline at end of file