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POPossible buffer overflow issue
 

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  1. POPossible buffer overflow issue
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    <p>I have the following code written in C++ to extract a given range of text in a Piece Table data structure. Here is the function of class PieceTable that stores the given range of text in the character array <code>buffer</code> : </p> <pre><code>void PieceTable::getTextInRange(unsigned __int64 startPos, unsigned __int64 endPos, char buffer[]){ char* totalBuffer = new char[getSize() + 2]; getBuffer(totalBuffer); if(endPos &gt;= getSize()) endPos = getSize() - 1; cout&lt;&lt;"startPos : "&lt;&lt;startPos&lt;&lt;endl; cout&lt;&lt;"endPos : "&lt;&lt;endPos&lt;&lt;endl; memcpy(buffer, &amp;totalBuffer[startPos], endPos - startPos + 1); buffer[endPos - startPos + 2] = '\0'; if(totalBuffer != 0) delete[] totalBuffer; totalBuffer = 0; } </code></pre> <p>Here is the piece of code in the main method which i use to test this code : </p> <pre><code>temp2 = new char[end - start + 2]; //changing 2 to 3 solves the problem pieceTable.getTextInRange(Start, end, temp2); for(int i = 0; i&lt; end - start + 1; i++) cout&lt;&lt;temp2[i]; cout&lt;&lt;endl; if( temp2 != 0) { delete[] temp2; //this line causes the heap corruption error temp2 = 0; } </code></pre> <p>Declaration of <code>temp2</code> : <code>char* temp2;</code></p> <p>Whenever the program encounters the <code>delete[] temp2</code> statement, there is a heap corruption error. The problem does not occur if I allocate memory for temp2 as:<br> <code>temp2 = new char[end - start + 3]</code> So, basically changing the length solves the problem. I know that I am messing up with the lengths somewhere, but I can't figure out where.</p> <p>EDIT : getSize() :</p> <pre><code>__int64 PieceTable::getSize() { return dList.getLength(dList.getBack()); } </code></pre> <p>I am using a piece table data structure. Here it is, inside this paper:http://www.cs.unm.edu/~crowley/papers/sds.pdf</p> <p>I may be wrong, but I don't think that there is any problem with <code>getSize()</code>, since the function I use to retrieve the length of the entire buffer <code>getBuffer</code>, works as shown in the code. </p>
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    1. PO
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    1. This table or related slice is empty.
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    1. USdevjeetroy
    1. USdevjeetroy
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    1. This table or related slice is empty.
    1. This table or related slice is empty.
    1. This table or related slice is empty.
    1. PO
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      1. PTAnswer
    2. PO
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    3. PO
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    1. This table or related slice is empty.
    1. COPrint the return value of `getSize() + 2` and also the value of `endPos - startPos + 2` to make sure that the former is larger than the latter.
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      1. POPossible buffer overflow issue
      1. USSeth Carnegie
    2. COactually, `getSize() + 2` is used for the variable `totalBuffer`, which is a local variable in the function `getTextInRange`.
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      1. POPossible buffer overflow issue
      1. USdevjeetroy
    3. COWhat was your initial allocation?
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      1. POPossible buffer overflow issue
      1. USVlad
 

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