linux-kernel - Re: [PATCH 04/14] pstore/ram: Should zap persistent zone on unlink

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Date:	Fri, 18 May 2012 16:52:57 -0700
From:	Colin Cross <ccross@...roid.com>
To:	Anton Vorontsov <anton.vorontsov@...aro.org>
Cc:	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	Kees Cook <keescook@...omium.org>,
	Tony Luck <tony.luck@...el.com>, Arnd Bergmann <arnd@...db.de>,
	John Stultz <john.stultz@...aro.org>,
	Shuah Khan <shuahkhan@...il.com>, arve@...roid.com,
	Rebecca Schultz Zavin <rebecca@...roid.com>,
	Jesper Juhl <jj@...osbits.net>,
	Randy Dunlap <rdunlap@...otime.net>,
	Stephen Boyd <sboyd@...eaurora.org>,
	Thomas Meyer <thomas@...3r.de>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Marco Stornelli <marco.stornelli@...il.com>,
	WANG Cong <xiyou.wangcong@...il.com>,
	linux-kernel@...r.kernel.org, devel@...verdev.osuosl.org,
	linaro-kernel@...ts.linaro.org, patches@...aro.org,
	kernel-team@...roid.com
Subject: Re: [PATCH 04/14] pstore/ram: Should zap persistent zone on unlink

On Fri, May 18, 2012 at 3:24 PM, Anton Vorontsov
<anton.vorontsov@...aro.org> wrote:
> Otherwise, unlinked file will reappear on the next boot.
>
> Reported-by: Kees Cook <keescook@...omium.org>
> Signed-off-by: Anton Vorontsov <anton.vorontsov@...aro.org>
> ---
>  fs/pstore/ram.c            |    1 +
>  fs/pstore/ram_core.c       |    6 ++++++
>  include/linux/pstore_ram.h |    1 +
>  3 files changed, 8 insertions(+)
>
> diff --git a/fs/pstore/ram.c b/fs/pstore/ram.c
> index 3a7724b..43d9727 100644
> --- a/fs/pstore/ram.c
> +++ b/fs/pstore/ram.c
> @@ -186,6 +186,7 @@ static int ramoops_pstore_erase(enum pstore_type_id type, u64 id,
>                return -EINVAL;
>
>        persistent_ram_free_old(cxt->przs[id]);
> +       persistent_ram_zap(cxt->przs[id]);
>
>        return 0;
>  }
> diff --git a/fs/pstore/ram_core.c b/fs/pstore/ram_core.c
> index dff5127..28b6d7f 100644
> --- a/fs/pstore/ram_core.c
> +++ b/fs/pstore/ram_core.c
> @@ -336,6 +336,12 @@ void persistent_ram_free_old(struct persistent_ram_zone *prz)
>        prz->old_log_size = 0;
>  }
>
> +void persistent_ram_zap(struct persistent_ram_zone *prz)
> +{
> +       atomic_set(&prz->buffer->size, 0);

There are a couple places in the ringbuffer code that assume that the
data is located in the buffer in the range [0, size).  It may start
anywhere in that range and wrap, but address 0 in the buffer always
contains data.  Resetting size to 0 but leaving start non-zero may
result in no data at address zero, and will cause problems in at least
persistent_ram_save_old, persistent_ram_ecc_old,
persistent_ram_copy_old, and the detection code in
persistent_ram_post_init.  These would all need to be fixed to support
the dual-metadata ringbuffer option I mentioned in response to patch
3, but if you don't like that idea then just clear start here.

> +       persistent_ram_update_header_ecc(prz);
> +}
> +
>  static void *persistent_ram_vmap(phys_addr_t start, size_t size)
>  {
>        struct page **pages;
> diff --git a/include/linux/pstore_ram.h b/include/linux/pstore_ram.h
> index 07d59b7..085199e 100644
> --- a/include/linux/pstore_ram.h
> +++ b/include/linux/pstore_ram.h
> @@ -69,6 +69,7 @@ struct persistent_ram_zone * __init persistent_ram_new(phys_addr_t start,
>                                                       size_t size,
>                                                       bool ecc);
>  void persistent_ram_free(struct persistent_ram_zone *prz);
> +void persistent_ram_zap(struct persistent_ram_zone *prz);
>  struct persistent_ram_zone *persistent_ram_init_ringbuffer(struct device *dev,
>                bool ecc);
>
> --
> 1.7.9.2
>
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