Replacing compile-time safe calls of strcpy()-related functions with
strscpy() was always calling the full strscpy() logic when a builtin
would be better. For example:
char buf[16];
strcpy(buf, "yes");
would reduce to __builtin_memcpy(buf, "yes", 4), but not if it was:
strscpy(buf, yes, sizeof(buf));
Fix this by checking if all sizes are known at compile-time.
Cc: linux-hardening@vger.kernel.org
Tested-by: Nathan Chancellor <nathan@kernel.org>
Signed-off-by: Kees Cook <keescook@chromium.org>
