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/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

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;
diff --git a/tests/gif/CMakeLists.txt b/tests/gif/CMakeLists.txt
index 2b73749e..e58e6b09 100644
--- a/tests/gif/CMakeLists.txt
+++ b/tests/gif/CMakeLists.txt
@@ -4,6 +4,7 @@ LIST(APPEND TESTS_FILES
 	bug00227
 	gif_null
 	ossfuzz5700
+	php_bug_75571
 	uninitialized_memory_read
 )
 
diff --git a/tests/gif/Makemodule.am b/tests/gif/Makemodule.am
index 3199438f..5dbeac53 100644
--- a/tests/gif/Makemodule.am
+++ b/tests/gif/Makemodule.am
@@ -4,6 +4,7 @@ libgd_test_programs += \
 	gif/bug00227 \
 	gif/gif_null \
 	gif/ossfuzz5700 \
+	gif/php_bug_75571 \
 	gif/uninitialized_memory_read
 
 if HAVE_LIBPNG
@@ -26,4 +27,5 @@ EXTRA_DIST += \
 	gif/bug00066.gif \
 	gif/bug00066_exp.png \
 	gif/ossfuzz5700.gif \
+	gif/php_bug_75571.gif \
 	gif/unitialized_memory_read.gif
diff --git a/tests/gif/php_bug_75571.c b/tests/gif/php_bug_75571.c
new file mode 100644
index 00000000..d4fae3ae
--- /dev/null
+++ b/tests/gif/php_bug_75571.c
@@ -0,0 +1,28 @@
+/**
+ * Test that GIF reading does not loop infinitely
+ * 
+ * We are reading a crafted GIF image which has been truncated.  This would
+ * trigger an infinite loop formerly, but know bails out early, returning
+ * NULL from gdImageCreateFromGif().
+ *
+ * See also https://bugs.php.net/bug.php?id=75571.
+ */
+
+
+#include "gd.h"
+#include "gdtest.h"
+
+
+int main()
+{
+    gdImagePtr im;
+    FILE *fp;
+
+    fp = gdTestFileOpen2("gif", "php_bug_75571.gif");
+    gdTestAssert(fp != NULL);
+    im = gdImageCreateFromGif(fp);
+    gdTestAssert(im == NULL);
+    fclose(fp);
+
+    return gdNumFailures();
+}