From 2ac0b787399df718dc61219145f44a6ae99813aa Mon Sep 17 00:00:00 2001
From: Adam Shapiro <adamshapiro0@gmail.com>
Date: Tue, 23 Feb 2021 21:32:39 +0000
Subject: [PATCH] Fixed sparse conservativeResize() when both num cols and rows
 decreased.

The previous implementation caused a buffer overflow trying to calculate non-
zero counts for columns that no longer exist.
---
 Eigen/src/SparseCore/SparseMatrix.h |  6 ++++--
 test/sparse_basic.cpp               | 22 +++++++++++++++-------
 2 files changed, 19 insertions(+), 9 deletions(-)

diff --git a/Eigen/src/SparseCore/SparseMatrix.h b/Eigen/src/SparseCore/SparseMatrix.h
index 6e6cab3c0..616b4a0c2 100644
--- a/Eigen/src/SparseCore/SparseMatrix.h
+++ b/Eigen/src/SparseCore/SparseMatrix.h
@@ -579,10 +579,12 @@ class SparseMatrix
       else if (innerChange < 0) 
       {
         // Inner size decreased: allocate a new m_innerNonZeros
-        m_innerNonZeros = static_cast<StorageIndex*>(std::malloc((m_outerSize+outerChange+1) * sizeof(StorageIndex)));
+        m_innerNonZeros = static_cast<StorageIndex*>(std::malloc((m_outerSize + outerChange) * sizeof(StorageIndex)));
         if (!m_innerNonZeros) internal::throw_std_bad_alloc();
-        for(Index i = 0; i < m_outerSize; i++)
+        for(Index i = 0; i < m_outerSize + (std::min)(outerChange, Index(0)); i++)
           m_innerNonZeros[i] = m_outerIndex[i+1] - m_outerIndex[i];
+        for(Index i = m_outerSize; i < m_outerSize + outerChange; i++)
+          m_innerNonZeros[i] = 0;
       }
       
       // Change the m_innerNonZeros in case of a decrease of inner size
diff --git a/test/sparse_basic.cpp b/test/sparse_basic.cpp
index 5f8762172..17897fd61 100644
--- a/test/sparse_basic.cpp
+++ b/test/sparse_basic.cpp
@@ -587,30 +587,38 @@ template<typename SparseMatrixType> void sparse_basic(const SparseMatrixType& re
       inc.push_back(std::pair<StorageIndex,StorageIndex>(3,2));
       inc.push_back(std::pair<StorageIndex,StorageIndex>(3,0));
       inc.push_back(std::pair<StorageIndex,StorageIndex>(0,3));
-      
+      inc.push_back(std::pair<StorageIndex,StorageIndex>(0,-1));
+      inc.push_back(std::pair<StorageIndex,StorageIndex>(-1,0));
+      inc.push_back(std::pair<StorageIndex,StorageIndex>(-1,-1));
+
       for(size_t i = 0; i< inc.size(); i++) {
         StorageIndex incRows = inc[i].first;
         StorageIndex incCols = inc[i].second;
         SparseMatrixType m1(rows, cols);
         DenseMatrix refMat1 = DenseMatrix::Zero(rows, cols);
         initSparse<Scalar>(density, refMat1, m1);
-        
+
+        SparseMatrixType m2 = m1;
+        m2.makeCompressed();
+
         m1.conservativeResize(rows+incRows, cols+incCols);
+        m2.conservativeResize(rows+incRows, cols+incCols);
         refMat1.conservativeResize(rows+incRows, cols+incCols);
         if (incRows > 0) refMat1.bottomRows(incRows).setZero();
         if (incCols > 0) refMat1.rightCols(incCols).setZero();
-        
+
         VERIFY_IS_APPROX(m1, refMat1);
-        
+        VERIFY_IS_APPROX(m2, refMat1);
+
         // Insert new values
         if (incRows > 0) 
           m1.insert(m1.rows()-1, 0) = refMat1(refMat1.rows()-1, 0) = 1;
         if (incCols > 0) 
           m1.insert(0, m1.cols()-1) = refMat1(0, refMat1.cols()-1) = 1;
-          
+
         VERIFY_IS_APPROX(m1, refMat1);
-          
-          
+
+
       }
   }