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.schu...@phytec.de>
---
Changes:
        v2: Added check for circular backend
            Improved error message if content was found

 .../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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