Guard against negative shift in jbig2 huffman initialization

Depending on the code table, it's possible to have the largest PREFLEN
value in the huffman table to be > 32. This will, potentially, cause the
calcuation of ((FIRSTCODE[i - 1] + LENCOUNT[i - 1]) << 1 to overflow the
int value and cause a negative shift.

This Cl checks the shift value and failes the initialization if we would
shift a negative value.

Bug: chromium:709781
Change-Id: Ia165a01ba9412e31c5e5a43717d415fcb42eafe5
Reviewed-on: https://pdfium-review.googlesource.com/3990
Reviewed-by: Lei Zhang <thestig@chromium.org>
Reviewed-by: Nicolás Peña <npm@chromium.org>
Commit-Queue: dsinclair <dsinclair@chromium.org>

2 files changed, 12 insertions, 5 deletions

diff --git a/core/fxcodec/jbig2/JBig2_HuffmanTable.cpp b/core/fxcodec/jbig2/JBig2_HuffmanTable.cpp
index baf97567fb..3bb6ae620c 100644
--- a/core/fxcodec/jbig2/JBig2_HuffmanTable.cpp
+++ b/core/fxcodec/jbig2/JBig2_HuffmanTable.cpp
@@ -97,11 +97,10 @@ bool CJBig2_HuffmanTable::ParseFromCodedBuffer(CJBig2_BitStream* pStream) {
     ++NTEMP;
   }
 
-  InitCodes();
-  return true;
+  return InitCodes();
 }
 
-void CJBig2_HuffmanTable::InitCodes() {
+bool CJBig2_HuffmanTable::InitCodes() {
   int lenmax = 0;
   for (uint32_t i = 0; i < NTEMP; ++i)
     lenmax = std::max(PREFLEN[i], lenmax);
@@ -115,13 +114,21 @@ void CJBig2_HuffmanTable::InitCodes() {
   FIRSTCODE[0] = 0;
   LENCOUNT[0] = 0;
   for (int i = 1; i <= lenmax; ++i) {
-    FIRSTCODE[i] = (FIRSTCODE[i - 1] + LENCOUNT[i - 1]) << 1;
+    pdfium::base::CheckedNumeric<int> shifted;
+    shifted = FIRSTCODE[i - 1] + LENCOUNT[i - 1];
+    shifted <<= 1;
+    if (!shifted.IsValid())
+      return false;
+
+    FIRSTCODE[i] = shifted.ValueOrDie();
     int CURCODE = FIRSTCODE[i];
     for (uint32_t j = 0; j < NTEMP; ++j) {
       if (PREFLEN[j] == i)
         CODES[j] = CURCODE++;
     }
   }
+
+  return true;
 }
 
 void CJBig2_HuffmanTable::ExtendBuffers(bool increment) {
diff --git a/core/fxcodec/jbig2/JBig2_HuffmanTable.h b/core/fxcodec/jbig2/JBig2_HuffmanTable.h
index 58a3124881..b49fcebc9c 100644
--- a/core/fxcodec/jbig2/JBig2_HuffmanTable.h
+++ b/core/fxcodec/jbig2/JBig2_HuffmanTable.h
@@ -35,7 +35,7 @@ class CJBig2_HuffmanTable {
  private:
   void ParseFromStandardTable(const JBig2TableLine* pTable);
   bool ParseFromCodedBuffer(CJBig2_BitStream* pStream);
-  void InitCodes();
+  bool InitCodes();
   void ExtendBuffers(bool increment);
 
   bool m_bOK;