c
// Vulnerable Code
int (*compare_func)(const BIGNUM *, const BIGNUM *) = dsa->compare_bignums;
int cmp_result = compare_func(dsa->q, another_bignum);

// Patched Code
int cmp_result;
if (dsa->compare_bignums != NULL && dsa->q != NULL) {
    int (*compare_func)(const BIGNUM *, const BIGNUM *) = dsa->compare_bignums;
    cmp_result = compare_func(dsa->q, another_bignum); 
} else {
    // Handle error: either the function pointer or dsa->q is NULL
}
