Date: Wed, 24 Jul 2019 10:08:57 -0700 From: Linus Torvalds <torvalds@...ux-foundation.org> To: Rasmus Villemoes <linux@...musvillemoes.dk> Cc: Yann Droneaud <ydroneaud@...eya.com>, David Laight <David.Laight@...lab.com>, Joe Perches <joe@...ches.com>, "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>, Jonathan Corbet <corbet@....net>, Stephen Kitt <steve@....org>, Kees Cook <keescook@...omium.org>, Nitin Gote <nitin.r.gote@...el.com>, "jannh@...gle.com" <jannh@...gle.com>, "kernel-hardening@...ts.openwall.com" <kernel-hardening@...ts.openwall.com>, Andrew Morton <akpm@...ux-foundation.org> Subject: Re: [PATCH 1/2] string: Add stracpy and stracpy_pad mechanisms On Wed, Jul 24, 2019 at 6:09 AM Rasmus Villemoes <linux@...musvillemoes.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
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