EXP37-C. Call functions with the arguments intended by the API

An application programming interface (API) specifies how a function is intended to be called.  Calling a function with incorrect arguments can result in unexpected or unintended program behavior. Functions that are appropriately declared [[DCL07-A. Include the appropriate type information in function declarators]] will typically fail compilation if they are supplied with the wrong number or types of arguments. However, there are cases where supplying the incorrect arguments to a function will at best generate compiler warnings. These warnings should be resolved [[MSC00-A. Compile cleanly at high warning levels]], but do not prevent program compilation.

Non-Compliant Code Example: (function pointers)

In this example, the function pointer fp is used to refer to the function strchr(). However, fp is declared without a function prototype.  As a result there is no type checking performed on the call to fp(12,2);.

#include <stdio.h>
#include <string.h>

char *(*fp) ();

int main(void) {
  char *c;
  fp = strchr;
  c = fp(12, 2);
  printf("%s\n", c);

}

Compliant Solution: (function pointers)

Declaring fp with a function prototype corrects this example.

#include <string.h>

char *(*fp) (char const *, int);

int main(void) {
  char *c;
  fp = strchr;
  c = fp("Hello",'H');
  printf("%s\n", c);

}

Non-Compliant Code Example: (variadic functions)

The POSIX function open() [[Open Group 04]] is a variadic function with the following prototype:

int open(char const *path, int oflag, ... );

The open() function accepts a third argument to determine a newly created file's access mode. If open() is used to create a new file and the third argument is omitted, the file may be created with unintended access permissions [[FIO06-A. Create files with appropriate access permissions]].

In this non-compliant code example from a vulnerability in the useradd() function of the shadow-utils package CVE-2006-1174 , the third argument to open() has been accidentally omitted.

fd = open(ms, O_CREAT|O_EXCL|O_WRONLY|O_TRUNC);

Compliant Solution: (variadic functions)

To correct this example, a third argument is specified in the call to open().

/* ... */
int fd = open(file_name, O_CREAT | O_WRONLY, file_access_permissions);
if (fd == -1){
  /* Handle Error */
}
/* ... */

Risk Assessment

Calling a function with incorrect arguments can result in unexpected or unintended program behavior.

Related Vulnerabilities

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

References

[[ISO/IEC 9899-1999]] Forward, Section 6.9.1, "Function definitions"
[[Spinellis 06]] Section 2.6.1, "Incorrect Routine or Arguments"

EXP36-C. Do not convert pointers into more strictly aligned pointer types      03. Expressions (EXP)       EXP38-C. Do not call offsetof() on bit-field members or invalid types