ubifs: Enable authentication support

With the preparations all being done this patch now enables authentication
support for UBIFS. Authentication is enabled when the newly introduced
auth_key and auth_hash_name mount options are passed. auth_key provides
the key which is used for authentication whereas auth_hash_name provides
the hashing algorithm used for this FS. Passing these options make
authentication mandatory and only UBIFS images that can be authenticated
with the given key are allowed.

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

Documentation/filesystems/ubifs.txt

@@ -91,6 +91,13 @@ chk_data_crc		do not skip checking CRCs on data nodes
 compr=none              override default compressor and set it to "none"
 compr=lzo               override default compressor and set it to "lzo"
 compr=zlib              override default compressor and set it to "zlib"
+auth_key=		specify the key used for authenticating the filesystem.
+			Passing this option makes authentication mandatory.
+			The passed key must be present in the kernel keyring
+			and must be of type 'logon'
+auth_hash_name=		The hash algorithm used for authentication. Used for
+			both hashing and for creating HMACs. Typical values
+			include "sha256" or "sha512"
 
 
 Quick usage instructions

fs/ubifs/Kconfig

@@ -86,3 +86,13 @@ config UBIFS_FS_SECURITY
 	  the extended attribute support in advance.
 
 	  If you are not using a security module, say N.
+
+config UBIFS_FS_AUTHENTICATION
+	bool "UBIFS authentication support"
+	select CRYPTO_HMAC
+	help
+	  Enable authentication support for UBIFS. This feature offers protection
+	  against offline changes for both data and metadata of the filesystem.
+	  If you say yes here you should also select a hashing algorithm such as
+	  sha256, these are not selected automatically since there are many
+	  different options.

fs/ubifs/super.c

@@ -579,7 +579,9 @@ static int init_constants_early(struct ubifs_info *c)
 	c->ranges[UBIFS_REF_NODE].len  = UBIFS_REF_NODE_SZ;
 	c->ranges[UBIFS_TRUN_NODE].len = UBIFS_TRUN_NODE_SZ;
 	c->ranges[UBIFS_CS_NODE].len   = UBIFS_CS_NODE_SZ;
-	c->ranges[UBIFS_AUTH_NODE].len = UBIFS_AUTH_NODE_SZ;
+	c->ranges[UBIFS_AUTH_NODE].min_len = UBIFS_AUTH_NODE_SZ;
+	c->ranges[UBIFS_AUTH_NODE].max_len = UBIFS_AUTH_NODE_SZ +
+				UBIFS_MAX_HMAC_LEN;
 
 	c->ranges[UBIFS_INO_NODE].min_len  = UBIFS_INO_NODE_SZ;
 	c->ranges[UBIFS_INO_NODE].max_len  = UBIFS_MAX_INO_NODE_SZ;
@@ -935,6 +937,8 @@ static int check_volume_empty(struct ubifs_info *c)
  * Opt_no_chk_data_crc: do not check CRCs when reading data nodes
  * Opt_override_compr: override default compressor
  * Opt_assert: set ubifs_assert() action
+ * Opt_auth_key: The key name used for authentication
+ * Opt_auth_hash_name: The hash type used for authentication
  * Opt_err: just end of array marker
  */
 enum {
@@ -946,6 +950,8 @@ enum {
 	Opt_no_chk_data_crc,
 	Opt_override_compr,
 	Opt_assert,
+	Opt_auth_key,
+	Opt_auth_hash_name,
 	Opt_ignore,
 	Opt_err,
 };
@@ -958,6 +964,8 @@ static const match_table_t tokens = {
 	{Opt_chk_data_crc, "chk_data_crc"},
 	{Opt_no_chk_data_crc, "no_chk_data_crc"},
 	{Opt_override_compr, "compr=%s"},
+	{Opt_auth_key, "auth_key=%s"},
+	{Opt_auth_hash_name, "auth_hash_name=%s"},
 	{Opt_ignore, "ubi=%s"},
 	{Opt_ignore, "vol=%s"},
 	{Opt_assert, "assert=%s"},
@@ -1081,6 +1089,16 @@ static int ubifs_parse_options(struct ubifs_info *c, char *options,
 			kfree(act);
 			break;
 		}
+		case Opt_auth_key:
+			c->auth_key_name = kstrdup(args[0].from, GFP_KERNEL);
+			if (!c->auth_key_name)
+				return -ENOMEM;
+			break;
+		case Opt_auth_hash_name:
+			c->auth_hash_name = kstrdup(args[0].from, GFP_KERNEL);
+			if (!c->auth_hash_name)
+				return -ENOMEM;
+			break;
 		case Opt_ignore:
 			break;
 		default:
@@ -1260,6 +1278,19 @@ static int mount_ubifs(struct ubifs_info *c)
 
 	c->mounting = 1;
 
+	if (c->auth_key_name) {
+		if (IS_ENABLED(CONFIG_UBIFS_FS_AUTHENTICATION)) {
+			err = ubifs_init_authentication(c);
+			if (err)
+				goto out_free;
+		} else {
+			ubifs_err(c, "auth_key_name, but UBIFS is built without"
+				  " authentication support");
+			err = -EINVAL;
+			goto out_free;
+		}
+	}
+
 	err = ubifs_read_superblock(c);
 	if (err)
 		goto out_free;
@@ -1577,7 +1608,10 @@ static void ubifs_umount(struct ubifs_info *c)
 	free_wbufs(c);
 	free_orphans(c);
 	ubifs_lpt_free(c, 0);
+	ubifs_exit_authentication(c);
 
+	kfree(c->auth_key_name);
+	kfree(c->auth_hash_name);
 	kfree(c->cbuf);
 	kfree(c->rcvrd_mst_node);
 	kfree(c->mst_node);