[v2 PATCH] fscrypt: Allow modular crypto algorithms

[Herbert Xu]

On Sat, Dec 21, 2019 at 05:44:28PM -0600, Eric Biggers wrote:
>
> I'm not sure this is a good idea, since there will probably need to be more
> places where built-in code calls into fs/crypto/ too.

Clearly it's going to be too much trouble for now.  I may revisit
this once the fscrypt code has settled down a little.

However, we can at least build the algorithms as modules, like this:

---8<---
The commit 643fa9612bf1 ("fscrypt: remove filesystem specific
build config option") removed modular support for fs/crypto.  This
causes the Crypto API to be built-in whenever fscrypt is enabled.
This makes it very difficult for me to test modular builds of
the Crypto API without disabling fscrypt which is a pain.

As fscrypt is still evolving and it's developing new ties with the
fs layer, it's hard to build it as a module for now.

However, the actual algorithms are not required until a filesystem
is mounted.  Therefore we can allow them to be built as modules.

Signed-off-by: Herbert Xu <herbert@xxxxxxxxxxxxxxxxxxx>

diff --git a/fs/crypto/Kconfig b/fs/crypto/Kconfig
index ff5a1746cbae..ae929fbc0f29 100644
--- a/fs/crypto/Kconfig
+++ b/fs/crypto/Kconfig
@@ -1,7 +1,19 @@
 # SPDX-License-Identifier: GPL-2.0-only
 config FS_ENCRYPTION
 	bool "FS Encryption (Per-file encryption)"
+	select KEYS
 	select CRYPTO
+	select CRYPTO_SKCIPHER
+	select CRYPTO_HASH
+	help
+	  Enable encryption of files and directories.  This
+	  feature is similar to ecryptfs, but it is more memory
+	  efficient since it avoids caching the encrypted and
+	  decrypted pages in the page cache.  Currently Ext4,
+	  F2FS and UBIFS make use of this feature.
+
+config FS_ENCRYPTION_TRI
+	tristate
 	select CRYPTO_AES
 	select CRYPTO_CBC
 	select CRYPTO_ECB
@@ -9,10 +21,3 @@ config FS_ENCRYPTION
 	select CRYPTO_CTS
 	select CRYPTO_SHA512
 	select CRYPTO_HMAC
-	select KEYS
-	help
-	  Enable encryption of files and directories.  This
-	  feature is similar to ecryptfs, but it is more memory
-	  efficient since it avoids caching the encrypted and
-	  decrypted pages in the page cache.  Currently Ext4,
-	  F2FS and UBIFS make use of this feature.
diff --git a/fs/ext4/Kconfig b/fs/ext4/Kconfig
index ef42ab040905..5de0bcc50d37 100644
--- a/fs/ext4/Kconfig
+++ b/fs/ext4/Kconfig
@@ -10,6 +10,7 @@ config EXT3_FS
 	select CRC16
 	select CRYPTO
 	select CRYPTO_CRC32C
+	select FS_ENCRYPTION_TRI if FS_ENCRYPTION
 	help
 	  This config option is here only for backward compatibility. ext3
 	  filesystem is now handled by the ext4 driver.
diff --git a/fs/f2fs/Kconfig b/fs/f2fs/Kconfig
index 652fd2e2b23d..9ccaec60af47 100644
--- a/fs/f2fs/Kconfig
+++ b/fs/f2fs/Kconfig
@@ -6,6 +6,7 @@ config F2FS_FS
 	select CRYPTO
 	select CRYPTO_CRC32
 	select F2FS_FS_XATTR if FS_ENCRYPTION
+	select FS_ENCRYPTION_TRI if FS_ENCRYPTION
 	help
 	  F2FS is based on Log-structured File System (LFS), which supports
 	  versatile "flash-friendly" features. The design has been focused on
diff --git a/fs/ubifs/Kconfig b/fs/ubifs/Kconfig
index 69932bcfa920..ea2d43829c18 100644
--- a/fs/ubifs/Kconfig
+++ b/fs/ubifs/Kconfig
@@ -12,6 +12,7 @@ config UBIFS_FS
 	select CRYPTO_ZSTD if UBIFS_FS_ZSTD
 	select CRYPTO_HASH_INFO
 	select UBIFS_FS_XATTR if FS_ENCRYPTION
+	select FS_ENCRYPTION_TRI if FS_ENCRYPTION
 	depends on MTD_UBI
 	help
 	  UBIFS is a file system for flash devices which works on top of UBI.
-- 
Email: Herbert Xu <herbert@xxxxxxxxxxxxxxxxxxx>
Home Page: http://gondor.apana.org.au/~herbert/
PGP Key: http://gondor.apana.org.au/~herbert/pubkey.txt