Re: [PATCH 1/2] common: state: Add property to protect existing data

[Sascha Hauer <s.hauer@pengutronix.de>]

Sorry for replying only after reminding me. This patch is still
in my inbox as I have some problems with it. Anyway let's solve
them.

On Thu, Dec 14, 2017 at 04:51:36PM +0100, Daniel Schultz wrote:
> After an update to a newer barebox version with an enabled state
> framework, existing data in storage memories could be overwritten.
> 
> Add a new property to check in front of every write task, if the meta
> magic field only contains the magic number, zeros or ones.

What is the case you are trying to protect against? I assume partition
size changes and possibly old bootloaders with an old partitioning.
Could you explain?

Whatever solution we come up with should work for the circular backend
aswell.

What I am missing in this patch is a clear way how to overcome this
situation. For mtd it would be: erase the device and reset, but what
about devices that don't have to be erased? We might just need a -f aka
"I know what I am doing" parameter.

> 
> Signed-off-by: Daniel Schultz <d.schultz@phytec.de>
> ---
>  .../devicetree/bindings/barebox/barebox,state.rst     |  3 +++
>  common/state/backend_bucket_direct.c                  |  2 ++
>  common/state/backend_storage.c                        |  1 +
>  common/state/state.c                                  | 19 ++++++++++++++++++-
>  common/state/state.h                                  |  2 ++
>  5 files changed, 26 insertions(+), 1 deletion(-)
> 
> diff --git a/Documentation/devicetree/bindings/barebox/barebox,state.rst b/Documentation/devicetree/bindings/barebox/barebox,state.rst
> index cebb5f8..db5b041 100644
> --- a/Documentation/devicetree/bindings/barebox/barebox,state.rst
> +++ b/Documentation/devicetree/bindings/barebox/barebox,state.rst
> @@ -55,6 +55,9 @@ Optional Properties
>  * ``algo``: A HMAC algorithm used to detect manipulation of the data
>    or header, sensible values follow this pattern ``hmac(<HASH>)``,
>    e.g. ``hmac(sha256)``. Only available for the ``backend-type`` ``raw``.
> +* ``keep-previous-content``: Check if a the bucket meta magic field contains
> +  other data than the magic value. If so, the backend will not write the state
> +  to prevent unconditionally overwrites of existing data.
>  
>  .. note:: For the ``backend-storage-type`` the keyword ``noncircular`` is still
>     supported as a fall back to an old storage format. Recommendation is to not
> diff --git a/common/state/backend_bucket_direct.c b/common/state/backend_bucket_direct.c
> index 958696e..9d6a337 100644
> --- a/common/state/backend_bucket_direct.c
> +++ b/common/state/backend_bucket_direct.c
> @@ -69,6 +69,8 @@ static int state_backend_bucket_direct_read(struct state_backend_storage_bucket
>  	if (meta.magic == direct_magic) {
>  		read_len = meta.written_length;
>  	} else {
> +		if (meta.magic != ~0 && !!meta.magic)
> +			bucket->wrong_magic = 1;

This only handles the direct backend, but not the circular backend.

>  		if (!IS_ENABLED(CONFIG_STATE_BACKWARD_COMPATIBLE)) {
>  			dev_err(direct->dev, "No meta data header found\n");
>  			dev_dbg(direct->dev, "Enable backward compatibility or increase stride size\n");
> diff --git a/common/state/backend_storage.c b/common/state/backend_storage.c
> index c6ebe86..f0a169d 100644
> --- a/common/state/backend_storage.c
> +++ b/common/state/backend_storage.c
> @@ -152,6 +152,7 @@ int state_storage_read(struct state_backend_storage *storage,
>  	 * one we want to use.
>  	 */
>  	list_for_each_entry(bucket, &storage->buckets, bucket_list) {
> +		bucket->wrong_magic = 0;
>  		ret = bucket->read(bucket, &bucket->buf, &bucket->len);
>  		if (ret == -EUCLEAN)
>  			bucket->needs_refresh = 1;
> diff --git a/common/state/state.c b/common/state/state.c
> index 6399bd3..e110542 100644
> --- a/common/state/state.c
> +++ b/common/state/state.c
> @@ -44,6 +44,9 @@ int state_save(struct state *state)
>  	void *buf;
>  	ssize_t len;
>  	int ret;
> +	struct state_backend_storage_bucket *bucket;
> +	struct state_backend_storage *storage;
> +	bool has_content;
>  
>  	if (!state->dirty)
>  		return 0;
> @@ -55,7 +58,18 @@ int state_save(struct state *state)
>  		return ret;
>  	}
>  
> -	ret = state_storage_write(&state->storage, buf, len);
> +	storage = &state->storage;
> +	if (state->keep_prev_content) {
> +		has_content = 0;

has_content is only used in this if(){}, can you move its declaration
here?

> +		list_for_each_entry(bucket, &storage->buckets, bucket_list)
> +			has_content |= bucket->wrong_magic;
> +		if (has_content) {
> +			dev_dbg(&state->dev, "Found content on a backend.\n");

I think dev_dbg() is a bit quiet. This really deserves a warning saying
"Found foreign content on backend, won't overwrite.\n"

> +			goto out;

You should initialize 'ret' with some error value before not saving the
state.

Sascha

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