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V5005. OWASP. A value is being subtracted from the unsigned variable. This can result in an overflow. In such a case, the comparison operation can potentially behave unexpectedly.
The analyzer has detected a potential error related to an overflow.
The following operations are executed:
- some value is subtracted from an unsigned variable;
- the result is compared to some value (operators <, <=, >, >= are used).
If the overflow occurs during the subtraction, the check result might be different from what the programmer expects.
Here is the simple case:
unsigned A = ...;
int B = ...;
if (A - B > 1)
Array[A - B] = 'x';A developer wants to protect the code against the array overflow using the check, but it won't help if 'A < B'.
If A = 3 and B = 5, then 0x00000003u - 0x00000005i = FFFFFFFEu
According to the C++ standards, the 'A – B' expression has the 'unsigned int' type. It means that 'A – B' will equal 'FFFFFFFEu'. This number is higher than one. As a result, memory outside the array will be accessed.
There are two options to fix the code. First, you can use variables of signed types for calculations:
intptr_t A = ...;
intptr_t B = ...;
if (A - B > 1)
Array[A - B] = 'x';Second, you can change the condition: it should depend on the result we want to get and the input values. If 'B >= 0', write the following code:
unsigned A = ...;
int B = ...;
if (A > B + 1)
Array[A - B] = 'x';If the code is correct, disable the warning for the line using the '//-V5005' comment.
This diagnostic is classified as:
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