Fix CVE-2017-7885:

https://cve.mitre.org/cgi-bin/cvename.cgi?name=CVE-2017-7885
https://bugs.ghostscript.com/show_bug.cgi?id=697703

Patch copied from upstream source repository:

https://git.ghostscript.com/?p=jbig2dec.git;a=commit;h=258290340bb657c9efb44457f717b0d8b49f4aa3

From 258290340bb657c9efb44457f717b0d8b49f4aa3 Mon Sep 17 00:00:00 2001
From: Shailesh Mistry <shailesh.mistry@hotmail.co.uk>
Date: Wed, 3 May 2017 22:06:01 +0100
Subject: [PATCH] Bug 697703: Prevent integer overflow vulnerability.

Add extra check for the offset being greater than the size
of the image and hence reading off the end of the buffer.

Thank you to Dai Ge for finding this issue and suggesting a patch.
---
 jbig2_symbol_dict.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/jbig2_symbol_dict.c b/jbig2_symbol_dict.c
index 4acaba9..36225cb 100644
--- a/jbig2_symbol_dict.c
+++ b/jbig2_symbol_dict.c
@@ -629,7 +629,7 @@ jbig2_decode_symbol_dict(Jbig2Ctx *ctx,
                 byte *dst = image->data;
 
                 /* SumatraPDF: prevent read access violation */
-                if (size - jbig2_huffman_offset(hs) < image->height * stride) {
+                if ((size - jbig2_huffman_offset(hs) < image->height * stride) || (size < jbig2_huffman_offset(hs))) {
                     jbig2_error(ctx, JBIG2_SEVERITY_FATAL, segment->number, "not enough data for decoding (%d/%d)", image->height * stride,
                                 size - jbig2_huffman_offset(hs));
                     jbig2_image_release(ctx, image);
-- 
2.13.0

