Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 2620:137:e000::1:20 as permitted sender) client-ip=2620:137:e000::1:20;
MIME-Version: 1.0
References: <CAH2r5mtDFpaAWeGCtrfm_WPM6j-Gkt_O80=nKfp6y39aXaBr6w@mail.gmail.com>
 <CAHk-=wi+xbVq++uqW9YgWpHjyBHNB8a-xad+Xp23-B+eodLCEA@mail.gmail.com> <YwSWLH4Wp6yDMeKf@arm.com>
In-Reply-To: <YwSWLH4Wp6yDMeKf@arm.com>
From:   Linus Torvalds <torvalds@linux-foundation.org>
Date:   Tue, 23 Aug 2022 10:37:38 -0700
Message-ID: <CAHk-=whU7QiwWeO81Rf+KGh0rGS9CEfKUXc5eik+Z0GaVJgu4A@mail.gmail.com>
Subject: Re: strlcpy() notes (was Re: [GIT PULL] smb3 client fixes)
To:     Catalin Marinas <catalin.marinas@arm.com>
Cc:     Steve French <smfrench@gmail.com>,
        CIFS <linux-cifs@vger.kernel.org>,
        LKML <linux-kernel@vger.kernel.org>,
        linux-arch <linux-arch@vger.kernel.org>
Content-Type: text/plain; charset="UTF-8"
Precedence: bulk

On Tue, Aug 23, 2022 at 1:56 AM Catalin Marinas <catalin.marinas@arm.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