Using the value of a pointer to a FILE object after the associated file is closed is undefined behavior. (See undefined behavior 148.) Programs that close the standard streams (especially stdout but also stderr and stdin) must be careful not to use these streams in subsequent function calls, particularly those that implicitly operate on them (such as printf(), perror(), and getc()).

This rule can be generalized to other file representations.

Noncompliant Code Example

In this noncompliant code example, the stdout stream is used after it is closed:

#include <stdio.h>
 
int close_stdout(void) {
  if (fclose(stdout) == EOF) {
    return -1;
  }
 
  printf("stdout successfully closed.\n");
  return 0;
}

Compliant Solution

In this compliant solution, stdout is not used again after it is closed. This must remain true for the remainder of the program, or stdout must be assigned the address of an open file object. 

#include <stdio.h>
 
int close_stdout(void) {
  if (fclose(stdout) == EOF) {
    return -1;
  }

  fputs("stdout successfully closed.", stderr);
  return 0;
}

Risk Assessment

Using the value of a pointer to a FILE object after the associated file is closed is undefined behavior.

Automated Detection

Tool	Version	Checker	Description
Astrée			Supported
CodeSonar		IO.UAC	Use after close
Compass/ROSE
Coverity		USE_AFTER_FREE	Implemented
Helix QAC		DF2696, DF2697, DF2698
Klocwork		SV.INCORRECT_RESOURCE_HANDLING.URH
LDRA tool suite		48 D	Partially implemented
Parasoft C/C++test		CERT_C-FIO46-a	Do not use resources that have been freed
PC-lint Plus		2471	Fully supported
Polyspace Bug Finder		CERT C: Rule FIO46-C	Checks for use of previously closed resource (rule partially covered)
SonarQube C/C++ Plugin		S3588

Related Vulnerabilities

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

Bibliography