ubfis: authentication: Authenticate master node

The master node contains hashes over the root index node and the LPT.
This patch adds a HMAC to authenticate the master node itself.

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

1 files changed, 55 insertions, 6 deletions

diff --git a/fs/ubifs/master.c b/fs/ubifs/master.c
index 0ca9d3513b4d..5ea51bbd14c7 100644
--- a/fs/ubifs/master.c
+++ b/fs/ubifs/master.c
@@ -25,6 +25,42 @@
 #include "ubifs.h"
 
 /**
+ * ubifs_compare_master_node - compare two UBIFS master nodes
+ * @c: UBIFS file-system description object
+ * @m1: the first node
+ * @m2: the second node
+ *
+ * This function compares two UBIFS master nodes. Returns 0 if they are equal
+ * and nonzero if not.
+ */
+int ubifs_compare_master_node(struct ubifs_info *c, void *m1, void *m2)
+{
+	int ret;
+	int behind;
+	int hmac_offs = offsetof(struct ubifs_mst_node, hmac);
+
+	/*
+	 * Do not compare the common node header since the sequence number and
+	 * hence the CRC are different.
+	 */
+	ret = memcmp(m1 + UBIFS_CH_SZ, m2 + UBIFS_CH_SZ,
+		     hmac_offs - UBIFS_CH_SZ);
+	if (ret)
+		return ret;
+
+	/*
+	 * Do not compare the embedded HMAC aswell which also must be different
+	 * due to the different common node header.
+	 */
+	behind = hmac_offs + UBIFS_MAX_HMAC_LEN;
+
+	if (UBIFS_MST_NODE_SZ > behind)
+		return memcmp(m1 + behind, m2 + behind, UBIFS_MST_NODE_SZ - behind);
+
+	return 0;
+}
+
+/**
  * scan_for_master - search the valid master node.
  * @c: UBIFS file-system description object
  *
@@ -37,7 +73,7 @@ static int scan_for_master(struct ubifs_info *c)
 {
 	struct ubifs_scan_leb *sleb;
 	struct ubifs_scan_node *snod;
-	int lnum, offs = 0, nodes_cnt;
+	int lnum, offs = 0, nodes_cnt, err;
 
 	lnum = UBIFS_MST_LNUM;
 
@@ -69,12 +105,23 @@ static int scan_for_master(struct ubifs_info *c)
 		goto out_dump;
 	if (snod->offs != offs)
 		goto out;
-	if (memcmp((void *)c->mst_node + UBIFS_CH_SZ,
-		   (void *)snod->node + UBIFS_CH_SZ,
-		   UBIFS_MST_NODE_SZ - UBIFS_CH_SZ))
+	if (ubifs_compare_master_node(c, c->mst_node, snod->node))
 		goto out;
+
 	c->mst_offs = offs;
 	ubifs_scan_destroy(sleb);
+
+	if (!ubifs_authenticated(c))
+		return 0;
+
+	err = ubifs_node_verify_hmac(c, c->mst_node,
+				     sizeof(struct ubifs_mst_node),
+				     offsetof(struct ubifs_mst_node, hmac));
+	if (err) {
+		ubifs_err(c, "Failed to verify master node HMAC");
+		return -EPERM;
+	}
+
 	return 0;
 
 out:
@@ -381,7 +428,8 @@ int ubifs_write_master(struct ubifs_info *c)
 	c->mst_node->highest_inum = cpu_to_le64(c->highest_inum);
 
 	ubifs_copy_hash(c, c->zroot.hash, c->mst_node->hash_root_idx);
-	err = ubifs_write_node(c, c->mst_node, len, lnum, offs);
+	err = ubifs_write_node_hmac(c, c->mst_node, len, lnum, offs,
+				    offsetof(struct ubifs_mst_node, hmac));
 	if (err)
 		return err;
 
@@ -392,7 +440,8 @@ int ubifs_write_master(struct ubifs_info *c)
 		if (err)
 			return err;
 	}
-	err = ubifs_write_node(c, c->mst_node, len, lnum, offs);
+	err = ubifs_write_node_hmac(c, c->mst_node, len, lnum, offs,
+				    offsetof(struct ubifs_mst_node, hmac));
 
 	return err;
 }