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Noncompliant Code Example (Static Variables)

This In this noncompliant code example declares sample, the address of local variable str is assigned to the variable p as a pointer to a constant char with , which has file scope. The value of str is assigned to p within the dont_do_this() function. However, str has automatic storage duration, so the lifetime of str ends when the assignment itself is legal, but it is illegal for str to go out of scope while p holds its address, as happens at the end of dont_do_this() function exits.

const char *p;
void dont_do_this(void) {
    const char str[] = "This will change";
    p = str; /* dangerous */
    /* ... */
}

void innocuous(void) {
    const char str[] = "Surprise, surprise";
}
/* ... */
dont_do_this();
innocuous();
/* p might be pointing to "Surprise, surprise" */

As a result of this undefined behavior, it is likely that p will refer to the string literal "Surprise, surprise" after the call to the innocuous() function.

Compliant Solution (Similar Scope)

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Noncompliant Code Example (Return Values)

In this examplenoncompliant code sample, the function init_array() incorrectly returns a pointer to a local stack variable, which could be accessed by the caller.

char *init_array(void) {
   char array[10];
   /* Initialize array */
   return array;
}

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void init_array(char array[]) {
   /* Initialize array */
   return;
}

int main(int argc, char *argv[]) {
   char array[10];
   init_array(array);
   /* ... */
   return 0;
}

Noncompliant Code

In this noncompliant code sample, the function squirrel_away() stores a pointer to local stack variable local into a location pointed to by function parameter ptr_param. Since it an be assumed that the pointer variable to which ptr_param points remains alive upon squirrel_away()'s return, it is illegal for local to go out of scope.void squirrel_away(char **ptr_param) {
char local10;
/* Initialize array */
*ptr_param = local;
}

void rodent() {
char *ptr;
squirrel_away(&ptr);
/* ptr is live but invalid here */
}

Risk Assessment

Referencing an object outside of its lifetime can result in an attacker being able to run arbitrary code.

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