ecryptfs: added ecryptfs_mount_auth_tok_only mount parameter

This patch adds a new mount parameter 'ecryptfs_mount_auth_tok_only' to
force ecryptfs to use only authentication tokens which signature has
been specified at mount time with parameters 'ecryptfs_sig' and
'ecryptfs_fnek_sig'. In this way, after disabling the passthrough and
the encrypted view modes, it's possible to make available to users only
files encrypted with the specified authentication token.

Signed-off-by: Roberto Sassu <roberto.sassu@polito.it>
Cc: Dustin Kirkland <kirkland@canonical.com>
Cc: James Morris <jmorris@namei.org>
[Tyler: Clean up coding style errors found by checkpatch]
Signed-off-by: Tyler Hicks <tyhicks@linux.vnet.ibm.com>

fs/ecryptfs/ecryptfs_kernel.h

@@ -377,6 +377,7 @@ struct ecryptfs_mount_crypt_stat {
 #define ECRYPTFS_GLOBAL_ENCRYPT_FILENAMES      0x00000010
 #define ECRYPTFS_GLOBAL_ENCFN_USE_MOUNT_FNEK   0x00000020
 #define ECRYPTFS_GLOBAL_ENCFN_USE_FEK          0x00000040
+#define ECRYPTFS_GLOBAL_MOUNT_AUTH_TOK_ONLY    0x00000080
 	u32 flags;
 	struct list_head global_auth_tok_list;
 	struct mutex global_auth_tok_list_mutex;

fs/ecryptfs/keystore.c

@@ -459,6 +459,15 @@ ecryptfs_find_auth_tok_for_sig(
 	if (ecryptfs_find_global_auth_tok_for_sig(&global_auth_tok,
 						  mount_crypt_stat, sig)) {
 
+		/* if the flag ECRYPTFS_GLOBAL_MOUNT_AUTH_TOK_ONLY is set in the
+		 * mount_crypt_stat structure, we prevent to use auth toks that
+		 * are not inserted through the ecryptfs_add_global_auth_tok
+		 * function.
+		 */
+		if (mount_crypt_stat->flags
+				& ECRYPTFS_GLOBAL_MOUNT_AUTH_TOK_ONLY)
+			return -EINVAL;
+
 		rc = ecryptfs_keyring_auth_tok_for_sig(auth_tok_key, auth_tok,
 						       sig);
 	} else

fs/ecryptfs/main.c

@@ -208,7 +208,8 @@ enum { ecryptfs_opt_sig, ecryptfs_opt_ecryptfs_sig,
        ecryptfs_opt_passthrough, ecryptfs_opt_xattr_metadata,
        ecryptfs_opt_encrypted_view, ecryptfs_opt_fnek_sig,
        ecryptfs_opt_fn_cipher, ecryptfs_opt_fn_cipher_key_bytes,
-       ecryptfs_opt_unlink_sigs, ecryptfs_opt_err };
+       ecryptfs_opt_unlink_sigs, ecryptfs_opt_mount_auth_tok_only,
+       ecryptfs_opt_err };
 
 static const match_table_t tokens = {
 	{ecryptfs_opt_sig, "sig=%s"},
@@ -223,6 +224,7 @@ static const match_table_t tokens = {
 	{ecryptfs_opt_fn_cipher, "ecryptfs_fn_cipher=%s"},
 	{ecryptfs_opt_fn_cipher_key_bytes, "ecryptfs_fn_key_bytes=%u"},
 	{ecryptfs_opt_unlink_sigs, "ecryptfs_unlink_sigs"},
+	{ecryptfs_opt_mount_auth_tok_only, "ecryptfs_mount_auth_tok_only"},
 	{ecryptfs_opt_err, NULL}
 };
 
@@ -406,6 +408,10 @@ static int ecryptfs_parse_options(struct ecryptfs_sb_info *sbi, char *options)
 		case ecryptfs_opt_unlink_sigs:
 			mount_crypt_stat->flags |= ECRYPTFS_UNLINK_SIGS;
 			break;
+		case ecryptfs_opt_mount_auth_tok_only:
+			mount_crypt_stat->flags |=
+				ECRYPTFS_GLOBAL_MOUNT_AUTH_TOK_ONLY;
+			break;
 		case ecryptfs_opt_err:
 		default:
 			printk(KERN_WARNING