[Rcpp-devel] ColDatum constructors memory safety

[Dirk Eddelbuettel]

Hi Alistair,

Thanks for sharing the analysis.

On 12 March 2010 at 15:15, Alistair Gee wrote:
| The ColDatum default constructor does not initialize any fields except
| for "level". But the ColDatum *copy* constructor expects the "type"
| field to be properly initialized, b/c if type is COLTYPE_FACTOR, the
| copy constructor proceeds to allocate memory using the numLevels field
| (which is unreliable b/c numLevels was never initialized). See
| comments in source below:
| 
| ColDatum::ColDatum() : level(0) { };
| 
| ColDatum::ColDatum(const ColDatum& datum) {
|   // Need deep copy so contruction/destruction is synchronized.
|   s = datum.s;
|   x = datum.x;
|   i = datum.i;
|   type = datum.type;                // XXX datum.type was never initialized.
|   level = datum.level;
|   numLevels = datum.numLevels; // XXX datum.numLevels was never initialzed.
|   d = datum.d;
|   if (type == COLTYPE_FACTOR) {
|       levelNames = new std::string[numLevels];   // XXX numLevels was copied
| 
| // from datum.numLevels which
| 
| // was never initialized
|       for (int j = 0; j < numLevels; j++)
|           levelNames[j] = datum.levelNames[j];     // XXX datum.levelNames is
| 
| // an uninitialized pointer.
|   }
| }
| 
| This is a problem if one tries to create a vector of ColDatum, e.g.
| 
| vector<ColDatum> colDatumVector(10);
| 
| Here, the default constructor is used to first construct a ColDatum
| object (which will not have "type" and "levelNames" properly
| initialized). Then the copy constructor called by the vector
| constructor to create 10 copies.

ColDatum is part of what we now call the 'classic' API. It is not getting
much attention or love as we focus on the 'new' API. That said, the new API
still lacks coverage for data.frame (and Date or Datetime classes). 

If you can think of a fix, we'd give it a good luck.  

Else, if you had a patch to clarify the header or code file and maybe just
warn of the issue, that would help too.

Cheers, Dirk

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