Fix CVE-2017-10688:

http://bugzilla.maptools.org/show_bug.cgi?id=2712
https://cve.mitre.org/cgi-bin/cvename.cgi?name=CVE-2017-10688
https://security-tracker.debian.org/tracker/CVE-2017-10688

Patch lifted from upstream source repository (the changes to 'ChangeLog'
don't apply to the libtiff 4.0.8 release tarball).

3rd party Git reference:

https://github.com/vadz/libtiff/commit/6173a57d39e04d68b139f8c1aa499a24dbe74ba1

2017-06-30  Even Rouault <even.rouault at spatialys.com>

        * libtiff/tif_dirwrite.c: in TIFFWriteDirectoryTagCheckedXXXX()
        functions associated with LONG8/SLONG8 data type, replace assertion
that
        the file is BigTIFF, by a non-fatal error.
        Fixes http://bugzilla.maptools.org/show_bug.cgi?id=2712
        Reported by team OWL337



/cvs/maptools/cvsroot/libtiff/ChangeLog,v  <--  ChangeLog
new revision: 1.1259; previous revision: 1.1258
/cvs/maptools/cvsroot/libtiff/libtiff/tif_dirwrite.c,v  <-- 
libtiff/tif_dirwrite.c
new revision: 1.86; previous revision: 1.85

Index: libtiff/libtiff/tif_dirwrite.c
===================================================================
RCS file: /cvs/maptools/cvsroot/libtiff/libtiff/tif_dirwrite.c,v
retrieving revision 1.85
retrieving revision 1.86
diff -u -r1.85 -r1.86
--- libtiff/libtiff/tif_dirwrite.c	11 Jan 2017 16:09:02 -0000	1.85
+++ libtiff/libtiff/tif_dirwrite.c	30 Jun 2017 17:29:44 -0000	1.86
@@ -1,4 +1,4 @@
-/* $Id: tif_dirwrite.c,v 1.85 2017-01-11 16:09:02 erouault Exp $ */
+/* $Id: tif_dirwrite.c,v 1.86 2017-06-30 17:29:44 erouault Exp $ */
 
 /*
  * Copyright (c) 1988-1997 Sam Leffler
@@ -2111,7 +2111,10 @@
 {
 	uint64 m;
 	assert(sizeof(uint64)==8);
-	assert(tif->tif_flags&TIFF_BIGTIFF);
+	if( !(tif->tif_flags&TIFF_BIGTIFF) ) {
+		TIFFErrorExt(tif->tif_clientdata,"TIFFWriteDirectoryTagCheckedLong8","LONG8 not allowed for ClassicTIFF");
+		return(0);
+	}
 	m=value;
 	if (tif->tif_flags&TIFF_SWAB)
 		TIFFSwabLong8(&m);
@@ -2124,7 +2127,10 @@
 {
 	assert(count<0x20000000);
 	assert(sizeof(uint64)==8);
-	assert(tif->tif_flags&TIFF_BIGTIFF);
+	if( !(tif->tif_flags&TIFF_BIGTIFF) ) {
+		TIFFErrorExt(tif->tif_clientdata,"TIFFWriteDirectoryTagCheckedLong8","LONG8 not allowed for ClassicTIFF");
+		return(0);
+	}
 	if (tif->tif_flags&TIFF_SWAB)
 		TIFFSwabArrayOfLong8(value,count);
 	return(TIFFWriteDirectoryTagData(tif,ndir,dir,tag,TIFF_LONG8,count,count*8,value));
@@ -2136,7 +2142,10 @@
 {
 	int64 m;
 	assert(sizeof(int64)==8);
-	assert(tif->tif_flags&TIFF_BIGTIFF);
+	if( !(tif->tif_flags&TIFF_BIGTIFF) ) {
+		TIFFErrorExt(tif->tif_clientdata,"TIFFWriteDirectoryTagCheckedLong8","SLONG8 not allowed for ClassicTIFF");
+		return(0);
+	}
 	m=value;
 	if (tif->tif_flags&TIFF_SWAB)
 		TIFFSwabLong8((uint64*)(&m));
@@ -2149,7 +2158,10 @@
 {
 	assert(count<0x20000000);
 	assert(sizeof(int64)==8);
-	assert(tif->tif_flags&TIFF_BIGTIFF);
+	if( !(tif->tif_flags&TIFF_BIGTIFF) ) {
+		TIFFErrorExt(tif->tif_clientdata,"TIFFWriteDirectoryTagCheckedLong8","SLONG8 not allowed for ClassicTIFF");
+		return(0);
+	}
 	if (tif->tif_flags&TIFF_SWAB)
 		TIFFSwabArrayOfLong8((uint64*)value,count);
 	return(TIFFWriteDirectoryTagData(tif,ndir,dir,tag,TIFF_SLONG8,count,count*8,value));