Skip to end of metadata
Go to start of metadata

A call to the fopen() or freopen() function must be matched with a call to fclose() before the lifetime of the last pointer that stores the return value of the call has ended or before normal program termination, whichever occurs first.

In general, this rule should also be applied to other functions with open and close resources, such as the POSIX open() and close() functions, or the Microsoft Windows CreateFile() and CloseHandle() functions.

Noncompliant Code Example

This code example is noncompliant because the file opened by the call to fopen() is not closed before function func() returns:

#include <stdio.h>
 
int func(const char *filename) {
  FILE *f = fopen(filename, "r"); 
  if (NULL == f) {
    return -1;
  }
  /* ... */
  return 0;
}

Compliant Solution

In this compliant solution, the file pointed to by f is closed before returning to the caller:

#include <stdio.h>
 
int func(const char *filename) {
  FILE *f = fopen(filename, "r"); 
  if (NULL == f) {
    return -1;
  }
  /* ... */
  if (fclose(f) == EOF) {
    return -1;
  }
  return 0;
}

Noncompliant Code Example (exit())

This code example is noncompliant because the resource allocated by the call to fopen() is not closed before the program terminates.  Although exit() closes the file, the program has no way of determining if an error occurs while flushing or closing the file.

#include <stdio.h>
#include <stdlib.h>
  
int main(void) {
  FILE *f = fopen(filename, "w"); 
  if (NULL == f) {
    exit(EXIT_FAILURE);
  }
  /* ... */
  exit(EXIT_SUCCESS);
}

Compliant Solution (exit())

In this compliant solution, the program closes f explicitly before calling exit(), allowing any error that occurs when flushing or closing the file to be handled appropriately:

#include <stdio.h>
#include <stdlib.h>

int main(void) {
  FILE *f = fopen(filename, "w"); 
  if (NULL == f) {
    /* Handle error */
  }
  /* ... */
  if (fclose(f) == EOF) {
    /* Handle error */
  }
  exit(EXIT_SUCCESS);
}

Noncompliant Code Example (POSIX)

This code example is noncompliant because the resource allocated by the call to open() is not closed before function func() returns:

#include <stdio.h>
#include <fcntl.h>
 
int func(const char *filename) {
  int fd = open(filename, O_RDONLY, S_IRUSR);
  if (-1 == fd) {
    return -1
  }
  /* ... */
  return 0;
}

Compliant Solution (POSIX)

In this compliant solution, fd is closed before returning to the caller:

#include <stdio.h>
#include <fcntl.h>
#include <unistd.h>
 
int func(const char *filename) {
  int fd = open(filename, O_RDONLY, S_IRUSR);
  if (-1 == fd) {
    return -1
  }
  /* ... */
  if (-1 == close(fd)) {
    return -1;
  }
  return 0;
}

Noncompliant Code Example (Windows)

In this noncompliant code example, the file opened by the Microsoft Windows CreateFile() function is not closed before func() returns:

#include <Windows.h>

int func(LPCTSTR filename) {
  HANDLE hFile = CreateFile(filename, GENERIC_READ, 0, NULL,
                            OPEN_EXISTING,
                            FILE_ATTRIBUTE_NORMAL, NULL);
  if (INVALID_HANDLE_VALUE == hFile) {
    return -1;
  }
  /* ... */
  return 0;
}

Compliant Solution (Windows)

In this compliant solution, hFile is closed by invoking the CloseHandle() function before returning to the caller:

#include <Windows.h>
 
int func(LPCTSTR filename) {
  HANDLE hFile = CreateFile(filename, GENERIC_READ, 0, NULL,
                            OPEN_EXISTING,
                            FILE_ATTRIBUTE_NORMAL, NULL);
  if (INVALID_HANDLE_VALUE == hFile) {
    return -1;
  } 
  /* ... */ 
  if (!CloseHandle(hFile)) {
    return -1;
  }
 
  return 0;
}

Risk Assessment

Failing to properly close files may allow an attacker to exhaust system resources and can increase the risk that data written into in-memory file buffers will not be flushed in the event of abnormal program termination.

Rule

Severity

Likelihood

Remediation Cost

Priority

Level

FIO42-C

Medium

Unlikely

Medium

P4

L3

Automated Detection

This rule is stricter than rule [fileclose] in ISO/IEC TS 17961:2013. Analyzers that conform to the technical standard may not detect all violations of this rule.

Tool

Version

Checker

Description

Astrée
19.04

Supported, but no explicit checker
CodeSonar
5.2p0
ALLOC.LEAKLeak
Compass/ROSE


Coverity
2017.07

RESOURCE_LEAK (partial)

Partially implemented
Klocwork
2018

RH.LEAK


LDRA tool suite
9.7.1

49 D

Partially implemented
Parasoft C/C++test
10.4.2

CERT_C-FIO42-a

Ensure resources are freed

Polyspace Bug Finder

R2019b

CERT C: Rule FIO42-CChecks for resource leak (rule partially covered)
PRQA QA-C

9.7

2701, 2702, 2703
PRQA QA-C++

 4.4

2701, 2702, 2703
SonarQube C/C++ Plugin

3.11

S2095

Related Vulnerabilities

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

Related Guidelines

Key here (explains table format and definitions)

Taxonomy

Taxonomy item

Relationship

CERT CFIO51-CPP. Close files when they are no longer neededPrior to 2018-01-12: CERT: Unspecified Relationship
CERT Oracle Secure Coding Standard for JavaFIO04-J. Release resources when they are no longer neededPrior to 2018-01-12: CERT: Unspecified Relationship
ISO/IEC TS 17961:2013Failing to close files or free dynamic memory when they are no longer needed [fileclose]Prior to 2018-01-12: CERT: Unspecified Relationship
CWE 2.11CWE-404, Improper Resource Shutdown or Release2017-07-06: CERT: Rule subset of CWE
CWE 2.11CWE-4592017-07-06: CERT: Rule subset of CWE
CWE 2.11CWE-7722017-07-06: CERT: Rule subset of CWE
CWE 2.11CWE-7732017-07-06: CERT: Rule subset of CWE
CWE 2.11CWE-7752017-07-06: CERT: Rule subset of CWE
CWE 2.11CWE-403

2017-10-30:MITRE:Unspecified Relationship

2018-10-18:CERT:Partial overlap

CERT-CWE Mapping Notes

Key here for mapping notes

CWE-773/CWE-775 and FIO42-C

CWE-773 = CWE-775

CWE-773 = Union( FIO42-C, list) where list =

  • Failure to free resource handles besides files

CWE-404/CWE-459/CWE-771/CWE-772 and FIO42-C/MEM31-C

Intersection( FIO42-C, MEM31-C) = Ø

CWE-404 = CWE-459 = CWE-771 = CWE-772

CWE-404 = Union( FIO42-C, MEM31-C list) where list =

  • Failure to free resources besides files or memory chunks, such as mutexes)

CWE-403 and FIO42-C

CWE-403 FIO42-C = list, where list =

  • A process opens and closes a sensitive file descriptor, but also executes a child process while the file descriptor is open.

FIO42-C - CWE-403 = SPECIAL_CASES, where SPECIAL_CASES =

  • A program opens a file descriptor and fails to close it, but does not invoke any child processes while the file descriptor is open.

Bibliography

[IEEE Std 1003.1:2013]XSH, System Interfaces, open