MSC13-A. Detect and remove unused values

The presence of unused values may indicate significant logic errors. To prevent such errors unused values should be identified and removed from code.

Non-Compliant Code Example

In this example, p2 is assigned the value returned by bar(), but that value is never used. Note this example assumes that foo() and bar() return valid pointers (see [[DCL30-C. Do not refer to an object outside of its lifetime]]).

int *p1, *p2;
p1 = foo();
p2 = bar();

if (baz())
   return p1;
else
    p2 = p1;
return p2;

Compliant Solution

This example can be corrected many different ways depending on the intent of the programmer. In this compliant solution, p2 is initialized to NULL rather than the result of bar(). The call to bar() can be removed if bar() does not produce any side-effects.

int *p1 = foo();
int *p2 = NULL;
bar(); /* Removable if bar() does not produce any side-effects */
if (baz()) {
   return p1;
}
else {
  p2 = p1;
}
return p2;

Risk Assessment

Unused values may indicate significant logic errors, possibly resulting in a denial of service condition.

Automated Detection

The Coverity Prevent UNUSED_VALUE checker finds variables that are assigned pointer values returned from a function call but never used. Coverity Prevent cannot discover all violations of this rule so further verification is necessary.

Related Vulnerabilities

Search for vulnerabilities resulting from the violation of this rule on the CERT website.

References

Coverity 07 Coverity Prevent? User's Manual (3.3.0) (2007).