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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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