The logical AND and logical OR operators (&&, ||) exhibit "short circuit" operation. That is, the second operand is not evaluated if the result can be deduced solely by evaluating the first operand. Consequently, the second operand should not contain side effects because, if it does, it is not apparent whether the side effect occurs.
Non-Compliant Code Example
enum { max = 15 };
int i = /* initialize to user supplied value */;
if ( (i >= 0 && (i++) <= max) ) {
/* code */
}
It is unclear whether the value of i will be incremented as a result of evaluating the condition.
Compliant Solution
In this compliant solution, the behavior is identical and clearly apparent.
enum { max = 15 };
int i = /* initialize to user supplied value */;
if (i >= 0) {
i++;
if (i <= max) {
/* code */
}
}
Risk Assessment
Attempting to modify an object that is the second operand to the logical OR or AND operator may cause that object to take on an unexpected value. This can lead to unintended program behavior.
Recommendation |
Severity |
Likelihood |
Remediation Cost |
Priority |
Level |
|---|---|---|---|---|---|
EXP02-A |
1 (low) |
1 (unlikely) |
2 (medium) |
P2 |
L3 |
Automated Detection
The LDRA tool suite V 7.6.0 is able to detect violations of this recommendation.
Related Vulnerabilities
Search for vulnerabilities resulting from the violation of this rule on the CERT website.
References
[[ISO/IEC 9899-1999]] Section 6.5.13, "Logical AND operator," and Section 6.5.14, "Logical OR operator"
EXP01-A. Do not take the size of a pointer to determine the size of the pointed-to type 03. Expressions (EXP) EXP03-A. Do not assume the size of a structure is the sum of the of the sizes of its members