[PATCH 04/14] pstore/ram: Should zap persistent zone on unlink

[Colin Cross]

On Fri, May 18, 2012 at 3:24 PM, Anton Vorontsov
<anton.vorontsov at linaro.org> wrote:
> Otherwise, unlinked file will reappear on the next boot.
>
> Reported-by: Kees Cook <keescook at chromium.org>
> Signed-off-by: Anton Vorontsov <anton.vorontsov at linaro.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
>