Fix for CVE-2017-14864, CVE-2017-14862 and CVE-2017-14859

The invalid memory dereference in
Exiv2::getULong()/Exiv2::StringValueBase::read()/Exiv2::DataValue::read()
is caused further up the call-stack, by
v->read(pData, size, byteOrder) in TiffReader::readTiffEntry()
passing an invalid pData pointer (pData points outside of the Tiff
file). pData can be set out of bounds in the (size > 4) branch where
baseOffset() and offset are added to pData_ without checking whether
the result is still in the file. As offset comes from an untrusted
source, an attacker can craft an arbitrarily large offset into the
file.

This commit adds a check into the problematic branch, whether the
result of the addition would be out of bounds of the Tiff
file. Furthermore the whole operation is checked for possible
overflows.

src/tiffvisitor.cpp

@@ -47,6 +47,7 @@ EXIV2_RCSID("@(#) $Id$")
 #include <iostream>
 #include <iomanip>
 #include <cassert>
+#include <limits>
 
 // *****************************************************************************
 namespace {
@@ -1517,7 +1518,19 @@ namespace Exiv2 {
                 size = 0;
         }
         if (size > 4) {
+            // setting pData to pData_ + baseOffset() + offset can result in pData pointing to invalid memory,
+            // as offset can be arbitrarily large
+            if ((static_cast<uintptr_t>(baseOffset()) > std::numeric_limits<uintptr_t>::max() - static_cast<uintptr_t>(offset))
+             || (static_cast<uintptr_t>(baseOffset() + offset) > std::numeric_limits<uintptr_t>::max() - reinterpret_cast<uintptr_t>(pData_)))
+            {
+                throw Error(59);
+            }
+            if (pData_ + static_cast<uintptr_t>(baseOffset()) + static_cast<uintptr_t>(offset) > pLast_) {
+                throw Error(58);
+            }
             pData = const_cast<byte*>(pData_) + baseOffset() + offset;
+
+	    // check for size being invalid
             if (size > static_cast<uint32_t>(pLast_ - pData)) {
 #ifndef SUPPRESS_WARNINGS
                 EXV_ERROR << "Upper boundary of data for "