Re: [PATCH 1/2] string: Add stracpy and stracpy_pad mechanisms

[Linus Torvalds]

On Wed, Jul 24, 2019 at 6:09 AM Rasmus Villemoes
<linux@xxxxxxxxxxxxxxxxxx> wrote:
>
> The kernel's snprintf() does not behave in a non-standard way, at least
> not with respect to its return value.

Note that the kernels snprintf() *does* very much protect against the
overflow case - not by changing the return value, but simply by having

        /* Reject out-of-range values early.  Large positive sizes are
           used for unknown buffer sizes. */
        if (WARN_ON_ONCE(size > INT_MAX))
                return 0;

at the very top.

So you can't actually overflow in the kernel by using the repeated

        offset += vsnprintf( .. size - offset ..);

model.

Yes, it's the wrong thing to do, but it is still _safe_.

              Linus