Received-SPF: pass (google.com: best guess record for domain of linux-kernel-owner@vger.kernel.org designates 209.132.180.67 as permitted sender) client-ip=209.132.180.67;
MIME-Version: 1.0
In-Reply-To: <20181026180042.52199-5-joel@joelfernandes.org>
References: <20181026180042.52199-1-joel@joelfernandes.org> <20181026180042.52199-5-joel@joelfernandes.org>
From:   Kees Cook <keescook@chromium.org>
Date:   Fri, 26 Oct 2018 20:39:13 +0100
Message-ID: <CAGXu5jKtZjZVr=7dAHQPU0OGtBpEKDZBO68-RTvFLbK6qB+cEA@mail.gmail.com>
Subject: Re: [RFC 5/6] pstore: donot treat empty buffers as valid
To:     "Joel Fernandes (Google)" <joel@joelfernandes.org>
Cc:     LKML <linux-kernel@vger.kernel.org>, kernel-team@android.com,
        Anton Vorontsov <anton@enomsg.org>,
        Colin Cross <ccross@android.com>,
        Tony Luck <tony.luck@intel.com>
Content-Type: text/plain; charset="UTF-8"
Sender: linux-kernel-owner@vger.kernel.org
Precedence: bulk

On Fri, Oct 26, 2018 at 7:00 PM, Joel Fernandes (Google)
<joel@joelfernandes.org> wrote:
> pstore currently calls persistent_ram_save_old even if a buffer is
> empty. While this appears to work, it is simply not the right thing to
> do and could lead to bugs so lets avoid that. It also prevent misleading
> prints in the logs which claim the buffer is valid.

I need to be better convinced that a present zero length record is the
same as a non-present record. This seems true, but there is
potentially still metadata available from a backend. What were the
misleading prints in logs?

-Kees

>
> Signed-off-by: Joel Fernandes (Google) <joel@joelfernandes.org>
> ---
>  fs/pstore/ram_core.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/fs/pstore/ram_core.c b/fs/pstore/ram_core.c
> index 0792595ebcfb..1299aa3ea734 100644
> --- a/fs/pstore/ram_core.c
> +++ b/fs/pstore/ram_core.c
> @@ -495,7 +495,7 @@ static int persistent_ram_post_init(struct persistent_ram_zone *prz, u32 sig,
>
>         sig ^= PERSISTENT_RAM_SIG;
>
> -       if (prz->buffer->sig == sig) {
> +       if (prz->buffer->sig == sig && buffer_size(prz)) {
>                 if (buffer_size(prz) > prz->buffer_size ||
>                     buffer_start(prz) > buffer_size(prz))
>                         pr_info("found existing invalid buffer, size %zu, start %zu\n",
> --
> 2.19.1.568.g152ad8e336-goog
>


-- 
Kees Cook