Re: [PATCH v2 1/2] common: state: Add property to protect existing data

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

On Thu, Apr 12, 2018 at 11:13:01AM +0200, 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.
> 
> Signed-off-by: Daniel Schultz <d.schultz@phytec.de>
> ---
> Changes:
> 	v2: Added check for circular backend
> 	    Improved error message if content was found
> 

Applied, thanks

Sascha

>  .../devicetree/bindings/barebox/barebox,state.rst     |  3 +++
>  common/state/backend_bucket_circular.c                |  8 +++++---
>  common/state/backend_bucket_direct.c                  |  2 ++
>  common/state/state.c                                  | 19 ++++++++++++++++++-
>  common/state/state.h                                  |  2 ++
>  5 files changed, 30 insertions(+), 4 deletions(-)
> 
> diff --git a/Documentation/devicetree/bindings/barebox/barebox,state.rst b/Documentation/devicetree/bindings/barebox/barebox,state.rst
> index 872bac0..2893937 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_circular.c b/common/state/backend_bucket_circular.c
> index 2324903..933493e 100644
> --- a/common/state/backend_bucket_circular.c
> +++ b/common/state/backend_bucket_circular.c
> @@ -396,11 +396,13 @@ static int state_backend_bucket_circular_init(
>  			meta = (struct state_backend_storage_bucket_circular_meta *)
>  					(buf + sub_offset + circ->writesize - sizeof(*meta));
>  
> -			if (meta->magic != circular_magic)
> +			if (meta->magic != circular_magic) {
>  				written_length = 0;
> -			else
> +				if (meta->magic != ~0 && !!meta->magic)
> +					bucket->wrong_magic = 1;
> +			} else {
>  				written_length = meta->written_length;
> -
> +			}
>  			break;
>  		}
>  	}
> 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;
>  		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/state.c b/common/state/state.c
> index 73dfb58..25d9502 100644
> --- a/common/state/state.c
> +++ b/common/state/state.c
> @@ -44,6 +44,8 @@ int state_save(struct state *state)
>  	void *buf;
>  	ssize_t len;
>  	int ret;
> +	struct state_backend_storage_bucket *bucket;
> +	struct state_backend_storage *storage;
>  
>  	if (!state->dirty)
>  		return 0;
> @@ -55,7 +57,19 @@ int state_save(struct state *state)
>  		return ret;
>  	}
>  
> -	ret = state_storage_write(&state->storage, buf, len);
> +	storage = &state->storage;
> +	if (state->keep_prev_content) {
> +		bool has_content = 0;
> +		list_for_each_entry(bucket, &storage->buckets, bucket_list)
> +			has_content |= bucket->wrong_magic;
> +		if (has_content) {
> +			dev_err(&state->dev, "Found foreign content on backend, won't overwrite.\n");
> +			ret = -EPERM;
> +			goto out;
> +		}
> +	}
> +
> +	ret = state_storage_write(storage, buf, len);
>  	if (ret) {
>  		dev_err(&state->dev, "Failed to write packed state, %d\n", ret);
>  		goto out;
> @@ -623,6 +637,9 @@ struct state *state_new_from_node(struct device_node *node, bool readonly)
>  
>  	of_property_read_string(node, "backend-storage-type", &storage_type);
>  
> +	state->keep_prev_content = of_property_read_bool(node,
> +							"keep-previous-content");
> +
>  	ret = state_format_init(state, backend_type, node, alias);
>  	if (ret)
>  		goto out_release_state;
> diff --git a/common/state/state.h b/common/state/state.h
> index 6670523..3a0662f 100644
> --- a/common/state/state.h
> +++ b/common/state/state.h
> @@ -46,6 +46,7 @@ struct state_backend_storage_bucket {
>  	void *buf;
>  	ssize_t len;
>  	bool needs_refresh;
> +	bool wrong_magic;
>  };
>  
>  /**
> @@ -105,6 +106,7 @@ struct state {
>  	char *of_path;
>  	const char *name;
>  	uint32_t magic;
> +	bool keep_prev_content;
>  
>  	struct list_head variables; /* Sorted list of variables */
>  
> -- 
> 2.7.4
> 
> 
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> 

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