Add vsnprintf() checks

include/stdio.h

@@ -0,0 +1,28 @@
+#ifndef FORTIFY_STDIO_H_
+#define FORTIFY_STDIO_H_
+
+#include_next <stdio.h>
+
+#if defined(_FORTIFY_SOURCE) && _FORTIFY_SOURCE > 0 && defined(__OPTIMIZE__) && __OPTIMIZE__ > 0
+
+static inline
+__attribute__ ((always_inline))
+__attribute__ ((__format__ (printf, 3, 0)))
+__attribute__ ((__nonnull__ (3)))
+int __fortify_vsnprintf(char *__restrict s, size_t n, const char *__restrict fmt, __va_list ap)
+{
+	size_t bos = __builtin_object_size(s, 0);
+
+	if (bos == (size_t)-1)
+		return vsnprintf(s, n, fmt, ap);
+	if (__builtin_constant_p(n) && n > bos)
+		__builtin_trap();
+	return vsnprintf(s, n, fmt, ap);
+}
+
+#undef vsnprintf
+#define vsnprintf(s, n, fmt, ap) __fortify_vsnprintf(s, n, fmt, ap)
+
+#endif
+
+#endif