ubifs: Add helper functions for authentication support

This patch adds the various helper functions needed for authentication
support. We need functions to hash nodes, to embed HMACs into a node and
to compare hashes and HMACs. Most functions first check if this
filesystem is authenticated and bail out early if not, which makes the
functions safe to be called with disabled authentication.

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

fs/ubifs/Kconfig

@@ -7,6 +7,7 @@ config UBIFS_FS
 	select CRYPTO if UBIFS_FS_ZLIB
 	select CRYPTO_LZO if UBIFS_FS_LZO
 	select CRYPTO_DEFLATE if UBIFS_FS_ZLIB
+	select CRYPTO_HASH_INFO
 	depends on MTD_UBI
 	help
 	  UBIFS is a file system for flash devices which works on top of UBI.

fs/ubifs/Makefile

@@ -8,3 +8,4 @@ ubifs-y += recovery.o ioctl.o lpt_commit.o tnc_misc.o debug.o
 ubifs-y += misc.o
 ubifs-$(CONFIG_UBIFS_FS_ENCRYPTION) += crypto.o
 ubifs-$(CONFIG_UBIFS_FS_XATTR) += xattr.o
+ubifs-$(CONFIG_UBIFS_FS_AUTHENTICATION) += auth.o