linux-kernel - Re: [RFC 5/6] pstore: donot treat empty buffers as valid

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Date:   Fri, 26 Oct 2018 20:39:13 +0100
From:   Kees Cook <keescook@...omium.org>
To:     "Joel Fernandes (Google)" <joel@...lfernandes.org>
Cc:     LKML <linux-kernel@...r.kernel.org>, kernel-team@...roid.com,
        Anton Vorontsov <anton@...msg.org>,
        Colin Cross <ccross@...roid.com>,
        Tony Luck <tony.luck@...el.com>
Subject: Re: [RFC 5/6] pstore: donot treat empty buffers as valid

On Fri, Oct 26, 2018 at 7:00 PM, Joel Fernandes (Google)
<joel@...lfernandes.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@...lfernandes.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