git-hardening/.crosslink/rules/c.md

C Best Practices

Memory Safety

• Always check return values of malloc/calloc
• Free all allocated memory (use tools like valgrind)
• Initialize all variables before use
• Use sizeof() with the variable, not the type

// GOOD: Safe memory allocation
int *arr = malloc(n * sizeof(*arr));
if (arr == NULL) {
    return -1;  // Handle allocation failure
}
// ... use arr ...
free(arr);

// BAD: Unchecked allocation
int *arr = malloc(n * sizeof(int));
arr[0] = 1;  // Crash if malloc failed

Buffer Safety

• Always bounds-check array access
• Use strncpy/snprintf instead of strcpy/sprintf
• Validate string lengths before copying

// GOOD: Safe string copy
char dest[64];
strncpy(dest, src, sizeof(dest) - 1);
dest[sizeof(dest) - 1] = '\0';

// BAD: Buffer overflow risk
char dest[64];
strcpy(dest, src);  // No bounds check

Security

• Never use gets() (use fgets())
• Validate all external input
• Use constant-time comparison for secrets
• Avoid integer overflow in size calculations