linux-kernel - Re: strlcpy() notes (was Re: [GIT PULL] smb3 client fixes)

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Date:   Tue, 23 Aug 2022 10:37:38 -0700
From:   Linus Torvalds <torvalds@...ux-foundation.org>
To:     Catalin Marinas <catalin.marinas@....com>
Cc:     Steve French <smfrench@...il.com>,
        CIFS <linux-cifs@...r.kernel.org>,
        LKML <linux-kernel@...r.kernel.org>,
        linux-arch <linux-arch@...r.kernel.org>
Subject: Re: strlcpy() notes (was Re: [GIT PULL] smb3 client fixes)

On Tue, Aug 23, 2022 at 1:56 AM Catalin Marinas <catalin.marinas@....com> wrote:
>
> With load_unaligned_zeropad(), the arm64 implementation disables tag
> checking temporarily. We could do the same with read_word_at_a_time()
> (there is a kasan_check_read() in this function but it wrongly uses a
> size of 1).

The "size of 1" is not wrong, it's intentional, exactly because people
do things like

    strscpy(dst, "string", sizeof(dst));

which is a bit unfortunate, but very understandable and intended to
work. So that thing may over-read the string by up to a word. And
KASAN ends up being unhappy.

            Linus