evm: replace HMAC version with attribute mask

Using HMAC version limits the posibility to arbitrarily add new
attributes such as SMACK64EXEC to the hmac calculation.

This patch replaces hmac version with attribute mask.
Desired attributes can be enabled with configuration parameter.
It allows to build kernels which works with previously labeled
filesystems.

Currently supported attribute is 'fsuuid' which is equivalent of
the former version 2.

Signed-off-by: Dmitry Kasatkin <d.kasatkin@samsung.com>
Signed-off-by: Mimi Zohar <zohar@linux.vnet.ibm.com>

security/integrity/evm/Kconfig

@@ -12,15 +12,24 @@ config EVM
 
 	  If you are unsure how to answer this question, answer N.
 
-config EVM_HMAC_VERSION
-	int "EVM HMAC version"
+if EVM
+
+menu "EVM options"
+
+config EVM_ATTR_FSUUID
+	bool "FSUUID (version 2)"
+	default y
 	depends on EVM
-	default 2
 	help
-	  This options adds EVM HMAC version support.
-	  1 - original version
-	  2 - add per filesystem unique identifier (UUID) (default)
+	  Include filesystem UUID for HMAC calculation.
+
+	  Default value is 'selected', which is former version 2.
+	  if 'not selected', it is former version 1
 
-	  WARNING: changing the HMAC calculation method or adding 
+	  WARNING: changing the HMAC calculation method or adding
 	  additional info to the calculation, requires existing EVM
-	  labeled file systems to be relabeled.  
+	  labeled file systems to be relabeled.
+
+endmenu
+
+endif

security/integrity/evm/evm.h

@@ -24,7 +24,10 @@
 extern int evm_initialized;
 extern char *evm_hmac;
 extern char *evm_hash;
-extern int evm_hmac_version;
+
+#define EVM_ATTR_FSUUID		0x0001
+
+extern int evm_hmac_attrs;
 
 extern struct crypto_shash *hmac_tfm;
 extern struct crypto_shash *hash_tfm;

security/integrity/evm/evm_crypto.c

@@ -112,7 +112,7 @@ static void hmac_add_misc(struct shash_desc *desc, struct inode *inode,
 	hmac_misc.gid = from_kgid(&init_user_ns, inode->i_gid);
 	hmac_misc.mode = inode->i_mode;
 	crypto_shash_update(desc, (const u8 *)&hmac_misc, sizeof(hmac_misc));
-	if (evm_hmac_version > 1)
+	if (evm_hmac_attrs & EVM_ATTR_FSUUID)
 		crypto_shash_update(desc, inode->i_sb->s_uuid,
 				    sizeof(inode->i_sb->s_uuid));
 	crypto_shash_final(desc, digest);

security/integrity/evm/evm_main.c

@@ -32,7 +32,7 @@ static char *integrity_status_msg[] = {
 };
 char *evm_hmac = "hmac(sha1)";
 char *evm_hash = "sha1";
-int evm_hmac_version = CONFIG_EVM_HMAC_VERSION;
+int evm_hmac_attrs;
 
 char *evm_config_xattrnames[] = {
 #ifdef CONFIG_SECURITY_SELINUX
@@ -57,6 +57,14 @@ static int __init evm_set_fixmode(char *str)
 }
 __setup("evm=", evm_set_fixmode);
 
+static void __init evm_init_config(void)
+{
+#ifdef CONFIG_EVM_ATTR_FSUUID
+	evm_hmac_attrs |= EVM_ATTR_FSUUID;
+#endif
+	pr_info("HMAC attrs: 0x%x\n", evm_hmac_attrs);
+}
+
 static int evm_find_protected_xattrs(struct dentry *dentry)
 {
 	struct inode *inode = dentry->d_inode;
@@ -432,6 +440,8 @@ static int __init init_evm(void)
 {
 	int error;
 
+	evm_init_config();
+
 	error = evm_init_secfs();
 	if (error < 0) {
 		pr_info("Error registering secfs\n");