The code calls sizeof() on a pointer type, which can be an incorrect calculation if the programmer intended to determine the size of the data that is being pointed to.
The use of sizeof() on a pointer can sometimes generate useful information. An obvious case is to find out the wordsize on a platform. More often than not, the appearance of sizeof(pointer) indicates a bug.
Threat Mapped score: 0.0
Industry: Finiancial
Threat priority: Unclassified
N/A
N/A
| Phase | Note |
|---|---|
| Implementation | N/A |
Intro: Care should be taken to ensure sizeof returns the size of the data structure itself, and not the size of the pointer to the data structure.
Body: In this example, sizeof(foo) returns the size of the pointer.
double *foo; ... foo = (double *)malloc(sizeof(foo));Intro: This example defines a fixed username and password. The AuthenticateUser() function is intended to accept a username and a password from an untrusted user, and check to ensure that it matches the username and password. If the username and password match, AuthenticateUser() is intended to indicate that authentication succeeded.
Body: In AuthenticateUser(), because sizeof() is applied to a parameter with an array type, the sizeof() call might return 4 on many modern architectures. As a result, the strncmp() call only checks the first four characters of the input password, resulting in a partial comparison (CWE-187), leading to improper authentication (CWE-287).
/* Ignore CWE-259 (hard-coded password) and CWE-309 (use of password system for authentication) for this example. */ char *username = "admin"; char *pass = "password"; int AuthenticateUser(char *inUser, char *inPass) { printf("Sizeof username = %d\n", sizeof(username)); printf("Sizeof pass = %d\n", sizeof(pass)); if (strncmp(username, inUser, sizeof(username))) { printf("Auth failure of username using sizeof\n"); return(AUTH_FAIL); } /* Because of CWE-467, the sizeof returns 4 on many platforms and architectures. */ if (! strncmp(pass, inPass, sizeof(pass))) { printf("Auth success of password using sizeof\n"); return(AUTH_SUCCESS); } else { printf("Auth fail of password using sizeof\n"); return(AUTH_FAIL); } } int main (int argc, char **argv) { int authResult; if (argc < 3) { ExitError("Usage: Provide a username and password"); } authResult = AuthenticateUser(argv[1], argv[2]); if (authResult != AUTH_SUCCESS) { ExitError("Authentication failed"); } else { DoAuthenticatedTask(argv[1]); } }