bugprone-unsafe-functions

Checks for functions that have safer, more secure replacements available, or are considered deprecated due to design flaws. The check heavily relies on the functions from the Annex K. “Bounds-checking interfaces” of C11.

The check implements the following rules from the CERT C Coding Standard:

cert-msc24-c and cert-msc33-c redirect here as aliases of this check.

Unsafe functions

If Annex K. is available, a replacement from Annex K. is suggested for the following functions:

asctime, asctime_r, bsearch, ctime, fopen, fprintf, freopen, fscanf, fwprintf, fwscanf, getenv, gets, gmtime, localtime, mbsrtowcs, mbstowcs, memcpy, memmove, memset, printf, qsort, scanf, snprintf, sprintf, sscanf, strcat, strcpy, strerror, strlen, strncat, strncpy, strtok, swprintf, swscanf, vfprintf, vfscanf, vfwprintf, vfwscanf, vprintf, vscanf, vsnprintf, vsprintf, vsscanf, vswprintf, vswscanf, vwprintf, vwscanf, wcrtomb, wcscat, wcscpy, wcslen, wcsncat, wcsncpy, wcsrtombs, wcstok, wcstombs, wctomb, wmemcpy, wmemmove, wprintf, wscanf.

If Annex K. is not available, replacements are suggested only for the following functions from the previous list:

  • asctime, asctime_r, suggested replacement: strftime

  • gets, suggested replacement: fgets

The following functions are always checked, regardless of Annex K availability:

  • rewind, suggested replacement: fseek

  • setbuf, suggested replacement: setvbuf

If ReportMoreUnsafeFunctions is enabled, the following functions are also checked:

  • bcmp, suggested replacement: memcmp

  • bcopy, suggested replacement: memcpy_s if Annex K is available, or memcpy

  • bzero, suggested replacement: memset_s if Annex K is available, or memset

  • getpw, suggested replacement: getpwuid

  • vfork, suggested replacement: posix_spawn

Although mentioned in the associated CERT rules, the following functions are ignored by the check:

atof, atoi, atol, atoll, tmpfile.

The availability of Annex K is determined based on the following macros:

  • __STDC_LIB_EXT1__: feature macro, which indicates the presence of Annex K. “Bounds-checking interfaces” in the library implementation

  • __STDC_WANT_LIB_EXT1__: user-defined macro, which indicates that the user requests the functions from Annex K. to be defined.

Both macros have to be defined to suggest replacement functions from Annex K. __STDC_LIB_EXT1__ is defined by the library implementation, and __STDC_WANT_LIB_EXT1__ must be defined to 1 by the user before including any system headers.

Options

ReportMoreUnsafeFunctions

When true, additional functions from widely used APIs (such as POSIX) are added to the list of reported functions. See the main documentation of the check for the complete list as to what this option enables. Default is true.

Examples

#ifndef __STDC_LIB_EXT1__
#error "Annex K is not supported by the current standard library implementation."
#endif

#define __STDC_WANT_LIB_EXT1__ 1

#include <string.h> // Defines functions from Annex K.
#include <stdio.h>

enum { BUFSIZE = 32 };

void Unsafe(const char *Msg) {
  static const char Prefix[] = "Error: ";
  static const char Suffix[] = "\n";
  char Buf[BUFSIZE] = {0};

  strcpy(Buf, Prefix); // warning: function 'strcpy' is not bounds-checking; 'strcpy_s' should be used instead.
  strcat(Buf, Msg);    // warning: function 'strcat' is not bounds-checking; 'strcat_s' should be used instead.
  strcat(Buf, Suffix); // warning: function 'strcat' is not bounds-checking; 'strcat_s' should be used instead.
  if (fputs(buf, stderr) < 0) {
    // error handling
    return;
  }
}

void UsingSafeFunctions(const char *Msg) {
  static const char Prefix[] = "Error: ";
  static const char Suffix[] = "\n";
  char Buf[BUFSIZE] = {0};

  if (strcpy_s(Buf, BUFSIZE, Prefix) != 0) {
    // error handling
    return;
  }

  if (strcat_s(Buf, BUFSIZE, Msg) != 0) {
    // error handling
    return;
  }

  if (strcat_s(Buf, BUFSIZE, Suffix) != 0) {
    // error handling
    return;
  }

  if (fputs(Buf, stderr) < 0) {
    // error handling
    return;
  }
}