Use of sizeof() on a Pointer Type
The code calls sizeof() on a malloced pointer type, which always returns the wordsize/8. This can produce an unexpected result if the programmer intended to determine how much memory has been allocated.
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.
The following examples help to illustrate the nature of this weakness and describe methods or techniques which can be used to mitigate the risk.
Note that the examples here are by no means exhaustive and any given weakness may have many subtle varieties, each of which may require different detection methods or runtime controls.
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.
In this example, sizeof(foo) returns the size of the pointer.
In this example, sizeof(*foo) returns the size of the data structure and not the size of the pointer.
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.
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).
Because of the partial comparison, any of these passwords would still cause authentication to succeed for the "admin" user:
Because only 4 characters are checked, this significantly reduces the search space for an attacker, making brute force attacks more feasible.
The same problem also applies to the username, so values such as "adminXYZ" and "administrator" will succeed for the username.
Weaknesses in this category are related to the rules and recommendations in the Memory Management (MEM) section of the SEI CERT C Coding Standard.
This category identifies Software Fault Patterns (SFPs) within the Incorrect Buffer Length Computation cluster (SFP10).
Weaknesses in this category are related to rules in the Arrays and the STL (ARR) section of the CERT C++ Secure Coding Standard. Since not all rules map to specific we...
This view (slice) covers all the elements in CWE.
This view contains a selection of weaknesses that represent the variety of weaknesses that are captured in CWE, at a level of abstraction that is likely to be useful t...
This view (slice) lists weaknesses that can be introduced during implementation.