476
}
If nresp has the value 1073741824 and sizeof(char*) has its typical value of 4, then the result of
the operation nresp*sizeof(char*) overflows, and the argument to xmalloc() will be 0. Most malloc()
implementations will happily allocate a 0-byte buffer, causing the subsequent loop iterations to
overflow the heap buffer response.
Example 3:
Integer overflows can be complicated and difficult to detect. The following example is an attempt to
show how an integer overflow may lead to undefined looping behavior:
Example Language: C (Bad)
short int bytesRec = 0;
char buf[SOMEBIGNUM];
while(bytesRec < MAXGET) {
bytesRec += getFromInput(buf+bytesRec);
}
In the above case, it is entirely possible that bytesRec may overflow, continuously creating a lower
number than MAXGET and also overwriting the first MAXGET-1 bytes of buf.
Example 4:
In this example the method determineFirstQuarterRevenue is used to determine the first quarter
revenue for an accounting/business application. The method retrieves the monthly sales totals for
the first three months of the year, calculates the first quarter sales totals from the monthly sales
totals, calculates the first quarter revenue based on the first quarter sales, and finally saves the first
quarter revenue results to the database.
Example Language: C (Bad)
#define JAN 1
#define FEB 2
#define MAR 3
short getMonthlySales(int month) {...}
float calculateRevenueForQuarter(short quarterSold) {...}
int determineFirstQuarterRevenue() {
// Variable for sales revenue for the quarter
float quarterRevenue = 0.0f;
short JanSold = getMonthlySales(JAN); /* Get sales in January */
short FebSold = getMonthlySales(FEB); /* Get sales in February */
short MarSold = getMonthlySales(MAR); /* Get sales in March */
// Calculate quarterly total
short quarterSold = JanSold + FebSold + MarSold;
// Calculate the total revenue for the quarter
quarterRevenue = calculateRevenueForQuarter(quarterSold);
saveFirstQuarterRevenue(quarterRevenue);
return 0;
}
However, in this example the primitive type short int is used for both the monthly and the quarterly
sales variables. In C the short int primitive type has a maximum value of 32768. This creates
a potential integer overflow if the value for the three monthly sales adds up to more than the
maximum value for the short int primitive type. An integer overflow can lead to data corruption,
unexpected behavior, infinite loops and system crashes. To correct the situation the appropriate
primitive type should be used, as in the example below, and/or provide some validation mechanism
to ensure that the maximum value for the primitive type is not exceeded.
Example Language: C (Good)
...
float calculateRevenueForQuarter(long quarterSold) {...}
CWE Version 4.14
CWE-190: Integer Overflow or Wraparound
CWE-190: Integer Overflow or Wraparound