linux-kernel - Re: [PATCH] lib/strscpy: avoid KASAN false positive

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Date:   Tue, 18 Jul 2017 13:26:17 -0700
From:   Linus Torvalds <torvalds@...ux-foundation.org>
To:     Andrey Ryabinin <aryabinin@...tuozzo.com>
Cc:     Andrew Morton <akpm@...ux-foundation.org>,
        Dave Jones <davej@...emonkey.org.uk>,
        Alexander Potapenko <glider@...gle.com>,
        Dmitry Vyukov <dvyukov@...gle.com>, kasan-dev@...glegroups.com,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] lib/strscpy: avoid KASAN false positive

On Tue, Jul 18, 2017 at 1:15 PM, Andrey Ryabinin
<aryabinin@...tuozzo.com> wrote:
>
> No, it does warn about valid users. The report that Dave posted wasn't about wrong strscpy() usage
> it was about reading 8-bytes from 5-bytes source string. It wasn't about buggy 'count' at all.
> So KASAN will warn for perfectly valid code like this:
>         char dest[16];
>         strscpy(dest, "12345", sizeof(dest)):

Ugh, ok, yes.

> For strscpy() that would mean making the *whole* read from 'src' buffer unchecked by KASAN.

So we do have that READ_ONCE_NOCHECK(), but could we perhaps have
something that doesn't do a NOCHECK but a partial check and is simply
ok with "this is an optimistc longer access"

We have that for the dcache case too, although there the code does
that odd kasan_unpoison_shadow() instead.

                 Linus