StarlingX/Security/Banned C Functions
Guidance
Prohibiting the use of banned functions is a good way to remove a significant number of potential code vulnerabilities from C and C++ code. This list is the compiled library of known bad functions that should be removed to reduce vulnerabilities. It is derived from experience with real-world security bugs and focuses primarily on functions that can lead to buffer overruns (reference: msdn). Specifically, for starling X, the main guidelines are that:
- Only functions in the standard C runtime library—libc—are mandated
- Unbounded functions are banned unless specifically noted
- Stack allocation functions are banned unless specifically approved by the project Core
There is no requirement to retrofit existing upstream code to meet these guidelines. A summary of the policy is provided below.
Func | Status |
strcpy, wcscpy | unbounded, banned; use strncpy |
strncpy | inspect for unterminated/truncated output |
strcat, wcscat | unbounded, banned; use strncat |
strncat | inspect for truncated output |
sprintf, vsprintf | unbounded, banned; use snprintf, vsnprintf |
snprintf | inspect for result fitting in buffer: snprintf(buf, size, ...) < size |
vsnprintf | banned except with approval from PSE. requires detailed inspection to avoid va_list pitfalls |
strtok | unbounded, banned; use strtok_r or strsep |
strtok_r, strsep | Inspect for terminated input buffer |
sscanf, vsscanf | unbounded, banned |
gets | unbounded, banned, use fgets() instead |
ato* | banned, use equivalent strto* functions |
*toa | Non-standard, inspect for output buffer length; prefer snprintf |
strlen, wcslen | banned except static strings; use strnlen with max length constant |
memcpy, memmove | allowed |
alloca | banned except with approval of PSE. requires detailed inspection to avoid stack overflow |
Color Coding
Allowed w/Inspection | Banned | Banned w/Exceptions |