linux-kernel - Re: [PATCH] lib/string: avoid reading beyond src buffer in strscpy

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Message-ID: <a67a79a6-5397-abc2-f222-bb4cb62ee6e3@virtuozzo.com>
Date:   Tue, 12 Dec 2017 19:06:12 +0300
From:   Andrey Ryabinin <aryabinin@...tuozzo.com>
To:     David Laight <David.Laight@...LAB.COM>,
        Kees Cook <keescook@...omium.org>,
        Dmitry Vyukov <dvyukov@...gle.com>
Cc:     Eryu Guan <eguan@...hat.com>, LKML <linux-kernel@...r.kernel.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Chris Metcalf <cmetcalf@...hip.com>,
        Alexander Potapenko <glider@...gle.com>,
        Linus Torvalds <torvalds@...ux-foundation.org>
Subject: Re: [PATCH] lib/string: avoid reading beyond src buffer in strscpy

On 12/12/2017 01:19 PM, David Laight wrote:
> From: Andrey Ryabinin
>> Sent: 11 December 2017 16:44
> ...
>> I suppose that depends on which one strscpy() caller you'd want to test.
>> Briefly looking at all current users, it doesn't look like they process huge amounts
>> of data through strscpy(), thus we shouldn't suffer from a slight
>> performance degradation of strscpy().
> 
> Don't most of the fast string functions use the same kind of
> optimisations.
> strlen() is very likely to do 64 bit reads and then shifts (etc)
> to determine whether any of the bytes are zero.
> 

See for yourself, strscpy() is the only sting function doing this.

> 	David
>