Fix CVE-2017-7975:

https://cve.mitre.org/cgi-bin/cvename.cgi?name=CVE-2017-7975
https://bugs.ghostscript.com/show_bug.cgi?id=697693

Patch copied from upstream source repository:

https://git.ghostscript.com/?p=jbig2dec.git;a=commit;h=f8992b8fe65c170c8624226f127c5c4bfed42c66

From f8992b8fe65c170c8624226f127c5c4bfed42c66 Mon Sep 17 00:00:00 2001
From: Shailesh Mistry <shailesh.mistry@hotmail.co.uk>
Date: Wed, 26 Apr 2017 22:12:14 +0100
Subject: [PATCH] Bug 697693: Prevent SEGV due to integer overflow.

While building a Huffman table, the start and end points were susceptible
to integer overflow.

Thank you to Jiaqi for finding this issue and suggesting a patch.
---
 jbig2_huffman.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/jbig2_huffman.c b/jbig2_huffman.c
index 511e461..b4189a1 100644
--- a/jbig2_huffman.c
+++ b/jbig2_huffman.c
@@ -421,8 +421,8 @@ jbig2_build_huffman_table(Jbig2Ctx *ctx, const Jbig2HuffmanParams *params)
 
             if (PREFLEN == CURLEN) {
                 int RANGELEN = lines[CURTEMP].RANGELEN;
-                int start_j = CURCODE << shift;
-                int end_j = (CURCODE + 1) << shift;
+                uint32_t start_j = CURCODE << shift;
+                uint32_t end_j = (CURCODE + 1) << shift;
                 byte eflags = 0;
 
                 if (end_j > max_j) {
-- 
2.13.0

