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Port libgd 7ff626c48a133eff1b6608bf28b1cfae30597408 to fix undefined behavior #23953

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Port libgd 7ff626c48a133eff1b6608bf28b1cfae30597408 to fix undefined behavior #23953

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2 changes: 1 addition & 1 deletion ext/gd/libgd/gd_gd2.c
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Original file line number Diff line number Diff line change
Expand Up @@ -164,7 +164,7 @@ static int _gd2GetHeader(gdIOCtxPtr in, int *sx, int *sy, int *cs, int *vers, in
gdFree(cidx);
goto fail1;
}
if (cidx[i].offset < 0 || cidx[i].size < 0) {
if (cidx[i].offset < 0 || cidx[i].size < 0 || cidx[i].size == INT_MAX) {
gdFree(cidx);
goto fail1;
}
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42 changes: 42 additions & 0 deletions ext/gd/tests/createfromstring-overflow.phpt
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Original file line number Diff line number Diff line change
@@ -0,0 +1,42 @@
--TEST--
imagecreatefromstring overflow with compressed chunk of size INT_MAX
--EXTENSIONS--
gd
--FILE--
<?php

// Documentation available at https://libgd.github.io/manuals/2.3.3/files/gd_gd2-c.html

@devnexen devnexen Sep 28, 2026 •
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nit: I think you can simplify the test like this

--- a/ext/gd/tests/createfromstring-overflow.phpt
+++ b/ext/gd/tests/createfromstring-overflow.phpt
@@ -4,37 +4,9 @@ imagecreatefromstring overflow with compressed chunk of size INT_MAX
 gd
 --FILE--
 <?php
-
-// Documentation available at https://libgd.github.io/manuals/2.3.3/files/gd_gd2-c.html
-$fileHeaderParts = [
-     "signature" => "gd2\x00",
-     "version" => "\x00\x02",
-     "width" => "\x00\x01",
-     "height" => "\x00\x01",
-     "chunk_size" => "\x00\x40",
-     "format" => "\x00\x04", // compressed truecolor image data
-     "x_chunk_count" => "\x00\x01",
-     "y_chunk_count" => "\x00\x01",
-];
-$fileHeader = implode("", $fileHeaderParts);
-
-$chunkHeaderParts = [
-     "offset" => "\x00\x00\x00\x20",
-     "size" =>"\x7F\xFF\xFF\xFF", // INT_MAX
-];
-$chunkHeader = implode("", $chunkHeaderParts);
-
-$trueColorHeaderParts = [
-     "truecolor" => "\x01",
-     "transparent" => "\x00\x00\x00\x00",
-];
-$trueColorHeader = implode("", $trueColorHeaderParts);
-
-$source = $fileHeader . $chunkHeader . $trueColorHeader;
-$img = imagecreatefromstring($source);
-var_dump($img);
-
+$data = pack('a4n7N2CN', 'gd2', 2, 1, 1, 64, 4, 1, 1, 0, 0x7FFFFFFF, 1, 0);
+var_dump(imagecreatefromstring($data));

@DanielEScherzer DanielEScherzer Sep 28, 2026

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Yes, that is possible, but it is entirely unclear to me what the pack string means and how these numbers do anything - is there a problem with having the clarity of array keys?

@devnexen devnexen Sep 28, 2026

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yes true you would need to know the gd2 format. but definitely not a blocker, the most imporant is the fix :)

$fileHeaderParts = [
"signature" => "gd2\x00",
"version" => "\x00\x02",
"width" => "\x00\x01",
"height" => "\x00\x01",
"chunk_size" => "\x00\x40",
"format" => "\x00\x04", // compressed truecolor image data
"x_chunk_count" => "\x00\x01",
"y_chunk_count" => "\x00\x01",
];
$fileHeader = implode("", $fileHeaderParts);

$chunkHeaderParts = [
"offset" => "\x00\x00\x00\x20",
"size" =>"\x7F\xFF\xFF\xFF", // INT_MAX
];
$chunkHeader = implode("", $chunkHeaderParts);

$trueColorHeaderParts = [
"truecolor" => "\x01",
"transparent" => "\x00\x00\x00\x00",
];
$trueColorHeader = implode("", $trueColorHeaderParts);

$source = $fileHeader . $chunkHeader . $trueColorHeader;
$img = imagecreatefromstring($source);
var_dump($img);

?>
--EXPECTF--
Warning: imagecreatefromstring(): Passed data is not in "GD2" format in %s on line %d

Warning: imagecreatefromstring(): Couldn't create GD Image Stream out of Data in %s on line %d
bool(false)
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