clang-tidy - bugprone-unsafe-functions — Extra Clang Tools 19.1.7 documentation

# Extra Clang Tools 19.1.7 documentation

## clang-tidy - bugprone-unsafe-functions

# 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:

  - Recommendation MSC24-C. Do not use deprecated or obsolescent functions.

  - Rule MSC33-C. Do not pass invalid data to the asctime() function.

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;
      }
    }