linux-kernel - Re: [PATCH] pstore/ram: fix for adding dumps to non-empty zone

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Message-ID: <201912301100.473042C@keescook>
Date:   Mon, 30 Dec 2019 11:02:07 -0800
From:   Kees Cook <keescook@...omium.org>
To:     Nikolai Merinov <n.merinov@...ngo-systems.com>
Cc:     Anton Vorontsov <anton@...msg.org>,
        Colin Cross <ccross@...roid.com>,
        Tony Luck <tony.luck@...el.com>, linux-kernel@...r.kernel.org,
        Aleksandr Yashkin <a.yashkin@...ngo-systems.com>,
        Ariel Gilman <a.gilman@...ngo-systems.com>
Subject: Re: [PATCH] pstore/ram: fix for adding dumps to non-empty zone

On Mon, Dec 23, 2019 at 06:38:16PM +0500, Nikolai Merinov wrote:
> From: Aleksandr Yashkin <a.yashkin@...ngo-systems.com>
> 
> The circle buffer in ramoops zones has a problem for adding a new
> oops dump to already an existing one.
> 
> The solution to this problem is to reset the circle buffer state before
> writing a new oops dump.

Can you describe the real-world problem you're fixing here? Dumps should
be appended as new records. Are you saying that once the circular list
is full, it blocks future dumps?

-Kees

> 
> Signed-off-by: Aleksandr Yashkin <a.yashkin@...ngo-systems.com>
> Signed-off-by: Nikolay Merinov <n.merinov@...ngo-systems.com>
> Signed-off-by: Ariel Gilman <a.gilman@...ngo-systems.com>
> 
> diff --git a/fs/pstore/ram.c b/fs/pstore/ram.c
> index 8caff834f002..33fceadbf515 100644
> --- a/fs/pstore/ram.c
> +++ b/fs/pstore/ram.c
> @@ -407,6 +407,13 @@ static int notrace ramoops_pstore_write(struct pstore_record *record)
>  
>  	prz = cxt->dprzs[cxt->dump_write_cnt];
>  
> +	/* Clean the buffer from old info.
> +	 * `ramoops_read_kmsg_hdr' expects to find a header in the beginning of
> +	 * buffer data, so we must to reset the buffer values, in order to
> +	 * ensure that the header will be written to the beginning of the buffer
> +	 */
> +	persistent_ram_zap(prz);
> +
>  	/* Build header and append record contents. */
>  	hlen = ramoops_write_kmsg_hdr(prz, record);
>  	if (!hlen)
> -- 
> 2.17.1
> 

-- 
Kees Cook