Prevent a division by zero error (fixes #141)

Bad /W in an xref stream could cause a division by zero error. Now
this is handled as a special case.

7 files changed, 38 insertions, 0 deletions

diff --git a/libqpdf/QPDF.cc b/libqpdf/QPDF.cc
index fc0c103f..d1360b14 100644
--- a/libqpdf/QPDF.cc
+++ b/libqpdf/QPDF.cc
@@ -917,6 +917,13 @@ QPDF::processXRefStream(qpdf_offset_t xref_offset, QPDFObjectHandle& xref_obj)
         }
 	entry_size += W[i];
     }
+    if (entry_size == 0)
+    {
+        throw QPDFExc(qpdf_e_damaged_pdf, this->file->getName(),
+                      "xref stream", xref_offset,
+                      "Cross-reference stream's /W indicates"
+                      " entry size of 0");
+    }
     long long max_num_entries =
         static_cast<unsigned long long>(-1) / entry_size;
 
diff --git a/libqpdf/QPDFWriter.cc b/libqpdf/QPDFWriter.cc
index 8ee322af..8d5f0682 100644
--- a/libqpdf/QPDFWriter.cc
+++ b/libqpdf/QPDFWriter.cc
@@ -2056,6 +2056,10 @@ QPDFWriter::generateObjectStreams()
     std::vector<QPDFObjGen> const& eligible =
         QPDF::Writer::getCompressibleObjGens(this->pdf);
     unsigned int n_object_streams = (eligible.size() + 99) / 100;
+    if (n_object_streams == 0)
+    {
+        throw std::logic_error("n_object_streams == 0");
+    }
     unsigned int n_per = eligible.size() / n_object_streams;
     if (n_per * n_object_streams < eligible.size())
     {
diff --git a/qpdf/qtest/qpdf.test b/qpdf/qtest/qpdf.test
index 12fb5dd2..89e41b36 100644
--- a/qpdf/qtest/qpdf.test
+++ b/qpdf/qtest/qpdf.test
@@ -218,6 +218,8 @@ my @bug_tests = (
     ["119", "other infinite loop", 3],
     ["120", "other infinite loop", 3],
     ["106", "zlib data error", 3],
+    ["141a", "/W entry size 0", 2],
+    ["141b", "/W entry size 0", 2],
     );
 $n_tests += scalar(@bug_tests);
 foreach my $d (@bug_tests)
diff --git a/qpdf/qtest/qpdf/issue-141a.out b/qpdf/qtest/qpdf/issue-141a.out
new file mode 100644
index 00000000..6182d90b
--- /dev/null
+++ b/qpdf/qtest/qpdf/issue-141a.out
@@ -0,0 +1,8 @@
+WARNING: issue-141a.pdf: can't find PDF header
+WARNING: issue-141a.pdf (xref stream: object 9 0, file position 10): stream dictionary lacks /Length key
+WARNING: issue-141a.pdf (xref stream: object 9 0, file position 47): attempting to recover stream length
+WARNING: issue-141a.pdf (xref stream: object 9 0, file position 47): unable to recover stream data; treating stream as empty
+WARNING: issue-141a.pdf: file is damaged
+WARNING: issue-141a.pdf (xref stream, file position 3): Cross-reference stream's /W indicates entry size of 0
+WARNING: issue-141a.pdf: Attempting to reconstruct cross-reference table
+issue-141a.pdf: unable to find trailer dictionary while recovering damaged file
diff --git a/qpdf/qtest/qpdf/issue-141a.pdf b/qpdf/qtest/qpdf/issue-141a.pdf
new file mode 100644
index 00000000..dec76be5
--- /dev/null
+++ b/qpdf/qtest/qpdf/issue-141a.pdf
@@ -0,0 +1,6 @@
+0009 0 obj<</Type/XRef/Size 0/W[0 0 0]>>stream
+endstream
+endobj
+startxref
+3
+%%EOF
diff --git a/qpdf/qtest/qpdf/issue-141b.out b/qpdf/qtest/qpdf/issue-141b.out
new file mode 100644
index 00000000..bf591243
--- /dev/null
+++ b/qpdf/qtest/qpdf/issue-141b.out
@@ -0,0 +1,5 @@
+WARNING: issue-141b.pdf: can't find PDF header
+WARNING: issue-141b.pdf: file is damaged
+WARNING: issue-141b.pdf (file position 7): xref not found
+WARNING: issue-141b.pdf: Attempting to reconstruct cross-reference table
+issue-141b.pdf: unable to find trailer dictionary while recovering damaged file
diff --git a/qpdf/qtest/qpdf/issue-141b.pdf b/qpdf/qtest/qpdf/issue-141b.pdf
new file mode 100644
index 00000000..67ce5ab8
--- /dev/null
+++ b/qpdf/qtest/qpdf/issue-141b.pdf
@@ -0,0 +1,6 @@
+%PDF-100 0 obj<</Type/XRef/Size 0/[]/W[0 0 0]/ 0>>stream
+0endstream
+endobj
+startxref
+7
+%%EOF
\ No newline at end of file