dsdb encrypted secrets module

Encrypt the samba secret attributes on disk.  This is intended to
mitigate the inadvertent disclosure of the sam.ldb file, and to mitigate
memory read attacks.

Currently the key file is stored in the same directory as sam.ldb but
this could be changed at a later date to use an HSM or similar mechanism
to protect the key.

Data is encrypted with AES 128 GCM. The encryption uses gnutls where
available and if it supports AES 128 GCM AEAD modes, otherwise nettle is
used.

Signed-off-by: Gary Lockyer <gary@catalyst.net.nz>
Reviewed-by: Andrew Bartlett <abartlet@samba.org>

librpc/idl/drsblobs.idl

@@ -721,4 +721,34 @@ interface drsblobs {
 	[nopython] void decode_ForestTrustInfo(
 		[in] ForestTrustInfo blob
 		);
+
+	typedef enum {
+		ENC_SECRET_AES_128_AEAD = 1
+	} EncryptedSecretAlgorithm;
+
+	const uint32 ENCRYPTED_SECRET_MAGIC_VALUE = 0xCA5CADED;
+
+	typedef [public] struct {
+		DATA_BLOB cleartext;
+	} PlaintextSecret;
+
+	/* The AEAD routines uses this as the additional authenticated data */
+	typedef [public] struct {
+		uint32 magic;
+		uint32 version;
+		uint32 algorithm;
+		uint32 flags;
+	} EncryptedSecretHeader;
+
+	typedef [public] struct {
+		/*
+		 * The iv is before the header to ensure that the first bytes of
+		 * the encrypted values are not predictable.
+		 * We do this so that if the decryption gets disabled, we don't
+		 * end up with predictable unicodePasswords.
+		 */
+		DATA_BLOB iv;
+		EncryptedSecretHeader header;
+		[flag(NDR_REMAINING)] DATA_BLOB encrypted;
+	} EncryptedSecret;
 }

source4/dsdb/samdb/ldb_modules/wscript

@@ -12,6 +12,38 @@ def set_options(opt):
     return
 
 def configure(conf):
+    conf.SET_TARGET_TYPE('nettle', 'EMPTY')
+    if conf.CHECK_CFG(
+        package="nettle",
+        args="--cflags --libs",
+        msg='Checking for nettle support'):
+
+        if conf.CHECK_FUNCS_IN(
+            'nettle_gcm_aes_encrypt',
+            'nettle',
+            headers='nettle/gcm.h'):
+
+            conf.DEFINE('HAVE_NETTLE_AES_GCM', '1')
+        else:
+            Logs.warn('No nettle support for AES GCM')
+    else:
+        Logs.warn('No nettle encryption libraries')
+
+    if conf.env.HAVE_GNUTLS:
+        if conf.CHECK_FUNCS_IN(
+            'gnutls_aead_cipher_init',
+            'gnutls',
+            headers='gnutls/gnutls.h'):
+
+                conf.DEFINE('HAVE_GNUTLS_AEAD', '1')
+        else:
+            Logs.warn('No gnutls support for AEAD encryption')
+
+    if not conf.env.HAVE_GNUTLS_AEAD and not conf.env.HAVE_NETTLE_AES_GCM:
+        conf.fatal("No AES GCM AEAD support"
+                   "Try installing gnutls if that does not support AEAD "
+                   "try installing nettle-dev or nettle-devel")
+
     conf.SET_TARGET_TYPE('gpgme', 'EMPTY')
 
     if Options.options.with_gpgme != False:

source4/dsdb/samdb/ldb_modules/wscript_build

@@ -28,6 +28,19 @@ bld.SAMBA_BINARY('test_unique_object_sids',
             DSDB_MODULE_HELPERS
         ''',
         install=False)
+bld.SAMBA_BINARY('test_encrypted_secrets',
+        source='tests/test_encrypted_secrets.c',
+        deps='''
+            talloc
+            samba-util
+            samdb-common
+            samdb
+            cmocka
+            nettle
+            gnutls
+            DSDB_MODULE_HELPERS
+        ''',
+        install=False)
 
 if bld.AD_DC_BUILD_IS_ENABLED():
     bld.PROCESS_SEPARATE_RULE("server")

source4/dsdb/samdb/ldb_modules/wscript_build_server

@@ -409,3 +409,20 @@ bld.SAMBA_MODULE('ldb_unique_object_sids',
 	deps='samdb-common DSDB_MODULE_HELPERS',
 	subsystem='ldb'
 	)
+
+bld.SAMBA_MODULE('ldb_encrypted_secrets',
+	source='encrypted_secrets.c',
+	subsystem='ldb',
+	init_function='ldb_encrypted_secrets_module_init',
+	module_init_name='ldb_init_module',
+	internal_module=False,
+	deps='''
+            talloc
+            samba-util
+            samdb-common
+            DSDB_MODULE_HELPERS
+            samdb
+            nettle
+            gnutls
+        '''
+	)

source4/dsdb/samdb/samdb.h

@@ -332,5 +332,6 @@ struct dsdb_extended_sec_desc_propagation_op {
 #define SAMBA_FEATURES_SUPPORTED_FLAG "@SAMBA_FEATURES_SUPPORTED"
 
 #define SAMBA_SORTED_LINKS_FEATURE "sortedLinks"
+#define SAMBA_ENCRYPTED_SECRETS_FEATURE "encryptedSecrets"
 
 #endif /* __SAMDB_H__ */

source4/selftest/tests.py

@@ -1008,3 +1008,5 @@ for env in ["ad_dc_ntvfs", "ad_dc", "fl2000dc", "fl2003dc", "fl2008r2dc", 'vampi
 #
 plantestsuite("samba4.dsdb.samdb.ldb_modules.unique_object_sids" , "none",
               [os.path.join(bindir(), "test_unique_object_sids")])
+plantestsuite("samba4.dsdb.samdb.ldb_modules.encrypted_secrets", "none",
+                  [os.path.join(bindir(), "test_encrypted_secrets")])