common: state: Add property to protect existing data

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 <[email protected]>
Signed-off-by: Sascha Hauer <[email protected]>

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

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;
 		}
 	}

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");

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;

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 */