ubifs: Add authentication nodes to journal

Nodes that are written to flash can only be authenticated through the
index after the next commit. When a journal replay is necessary the
nodes are not yet referenced by the index and thus can't be
authenticated.

This patch overcomes this situation by creating a hash over all nodes
beginning from the commit start node over the reference node(s) and
the buds themselves. From
time to time we insert authentication nodes. Authentication nodes
contain a HMAC from the current hash state, so that they can be
used to authenticate a journal replay up to the point where the
authentication node is. The hash is continued afterwards
so that theoretically we would only have to check the HMAC of
the last authentication node we find.

Overall we get this picture:

,,,,,,,,
,......,...........................................
,. CS  ,               hash1.----.           hash2.----.
,.  |  ,                    .    |hmac            .    |hmac
,.  v  ,                    .    v                .    v
,.REF#0,-> bud -> bud -> bud.-> auth -> bud -> bud.-> auth ...
,..|...,...........................................
,  |   ,
,  |   ,,,,,,,,,,,,,,,
.  |            hash3,----.
,  |                 ,    |hmac
,  v                 ,    v
, REF#1 -> bud -> bud,-> auth ...
,,,|,,,,,,,,,,,,,,,,,,
   v
  REF#2 -> ...
   |
   V
  ...

Note how hash3 covers CS, REF#0 and REF#1 so that it is not possible to
exchange or skip any reference nodes. Unlike the picture suggests the
auth nodes themselves are not hashed.

With this it is possible for an offline attacker to cut each journal
head or to drop the last reference node(s), but not to skip any journal
heads or to reorder any operations.

Signed-off-by: Sascha Hauer <s.hauer@pengutronix.de>
Signed-off-by: Richard Weinberger <richard@nod.at>

1 files changed, 8 insertions, 0 deletions

diff --git a/fs/ubifs/ubifs.h b/fs/ubifs/ubifs.h
index 67bfd58d28d4..600a25b93a80 100644
--- a/fs/ubifs/ubifs.h
+++ b/fs/ubifs/ubifs.h
@@ -717,6 +717,7 @@ struct ubifs_wbuf {
  * @jhead: journal head number this bud belongs to
  * @list: link in the list buds belonging to the same journal head
  * @rb: link in the tree of all buds
+ * @log_hash: the log hash from the commit start node up to this bud
  */
 struct ubifs_bud {
 	int lnum;
@@ -724,6 +725,7 @@ struct ubifs_bud {
 	int jhead;
 	struct list_head list;
 	struct rb_node rb;
+	struct shash_desc *log_hash;
 };
 
 /**
@@ -731,6 +733,7 @@ struct ubifs_bud {
  * @wbuf: head's write-buffer
  * @buds_list: list of bud LEBs belonging to this journal head
  * @grouped: non-zero if UBIFS groups nodes when writing to this journal head
+ * @log_hash: the log hash from the commit start node up to this journal head
  *
  * Note, the @buds list is protected by the @c->buds_lock.
  */
@@ -738,6 +741,7 @@ struct ubifs_jhead {
 	struct ubifs_wbuf wbuf;
 	struct list_head buds_list;
 	unsigned int grouped:1;
+	struct shash_desc *log_hash;
 };
 
 /**
@@ -1236,6 +1240,8 @@ struct ubifs_debug_info;
  * @auth_key_name: the authentication key name
  * @auth_hash_name: the name of the hash algorithm used for authentication
  * @auth_hash_algo: the authentication hash used for this fs
+ * @log_hash: the log hash from the commit start node up to the latest reference
+ *            node.
  *
  * @empty: %1 if the UBI device is empty
  * @need_recovery: %1 if the file-system needs recovery
@@ -1478,6 +1484,8 @@ struct ubifs_info {
 	char *auth_hash_name;
 	enum hash_algo auth_hash_algo;
 
+	struct shash_desc *log_hash;
+
 	/* The below fields are used only during mounting and re-mounting */
 	unsigned int empty:1;
 	unsigned int need_recovery:1;