From a11f47475e6443b7f32d21f2271f28f417e2ac04 Mon Sep 17 00:00:00 2001

From: "Christoph M. Becker" <cmbecker69@gmx.de>

Date: Wed, 29 Nov 2017 19:37:38 +0100

Subject: [PATCH] Fix #420: Potential infinite loop in gdImageCreateFromGifCtx

Due to a signedness confusion in `GetCode_` a corrupt GIF file can

trigger an infinite loop.  Furthermore we make sure that a GIF without

any palette entries is treated as invalid *after* open palette entries

have been removed.

CVE-2018-5711

See also https://bugs.php.net/bug.php?id=75571.

---

 src/gd_gif_in.c             |  12 ++++++------

 tests/gif/.gitignore        |   1 +

 tests/gif/CMakeLists.txt    |   1 +

 tests/gif/Makemodule.am     |   2 ++

 tests/gif/php_bug_75571.c   |  28 ++++++++++++++++++++++++++++

 tests/gif/php_bug_75571.gif | Bin 0 -> 1731 bytes

 6 files changed, 38 insertions(+), 6 deletions(-)

 create mode 100644 tests/gif/php_bug_75571.c

 create mode 100644 tests/gif/php_bug_75571.gif

diff --git a/src/gd_gif_in.c b/src/gd_gif_in.c

index daf26e79..0a8bd717 100644

--- a/src/gd_gif_in.c

+++ b/src/gd_gif_in.c

@@ -335,11 +335,6 @@ BGD_DECLARE(gdImagePtr) gdImageCreateFromGifCtx(gdIOCtxPtr fd)

 		return 0;

 	}

-	if(!im->colorsTotal) {

-		gdImageDestroy(im);

-		return 0;

-	}

-

 	/* Check for open colors at the end, so

 	 * we can reduce colorsTotal and ultimately

 	 * BitsPerPixel */

@@ -351,6 +346,11 @@ BGD_DECLARE(gdImagePtr) gdImageCreateFromGifCtx(gdIOCtxPtr fd)

 		}

 	}

+	if(!im->colorsTotal) {

+		gdImageDestroy(im);

+		return 0;

+	}

+

 	return im;

 }

@@ -447,7 +447,7 @@ static int

 GetCode_(gdIOCtx *fd, CODE_STATIC_DATA *scd, int code_size, int flag, int *ZeroDataBlockP)

 {

 	int i, j, ret;

-	unsigned char count;

+	int count;

 	if(flag) {

 		scd->curbit = 0;