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

Linus Torvalds
2019-07-24T17:09:20Z

On Wed, Jul 24, 2019 at 6:09 AM Rasmus Villemoes
<linux@rasmusvillemoes.dk> 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