fs: ubifs: Add authentication support

This adds UBIFS authentication support. For now, we do not do
any authentication even on authenticated UBIFS images. Since
this behaviour is not what the user normally expects when mounting
authenticated images we only do this when the user explicitly allows
it in "global.ubifs.allow_authenticated_unauthenticated". If the
flag is false then we refuse mounting such an image and return -EPERM
instead.

Signed-off-by: Sascha Hauer <s.hauer@pengutronix.de>

1 files changed, 53 insertions, 4 deletions

diff --git a/fs/ubifs/master.c b/fs/ubifs/master.c
index 40b49b6346..056699b616 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:
@@ -305,6 +352,8 @@ int ubifs_read_master(struct ubifs_info *c)
 	c->lst.total_dead  = le64_to_cpu(c->mst_node->total_dead);
 	c->lst.total_dark  = le64_to_cpu(c->mst_node->total_dark);
 
+	ubifs_copy_hash(c, c->mst_node->hash_root_idx, c->zroot.hash);
+
 	c->calc_idx_sz = c->bi.old_idx_sz;
 
 	if (c->mst_node->flags & cpu_to_le32(UBIFS_MST_NO_ORPHS))