[v3 PATCH] fscrypt: Allow modular crypto algorithms

[Herbert Xu]

On Sun, Dec 22, 2019 at 10:45:45AM -0600, Eric Biggers wrote:
> 
> Okay, this approach looks fine.  But can you rename the option to something more
> self-explanatory like FS_ENCRYPTION_ALGS, and add a comment?  Like:
> 
> # Filesystems supporting encryption must select this if FS_ENCRYPTION.  This
> # allows the algorithms to be built as modules when all the filesystems are.

Sure, here's a third revision.

---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..02df95b44331 100644
--- a/fs/crypto/Kconfig
+++ b/fs/crypto/Kconfig
@@ -2,13 +2,8 @@
 config FS_ENCRYPTION
 	bool "FS Encryption (Per-file encryption)"
 	select CRYPTO
-	select CRYPTO_AES
-	select CRYPTO_CBC
-	select CRYPTO_ECB
-	select CRYPTO_XTS
-	select CRYPTO_CTS
-	select CRYPTO_SHA512
-	select CRYPTO_HMAC
+	select CRYPTO_HASH
+	select CRYPTO_SKCIPHER
 	select KEYS
 	help
 	  Enable encryption of files and directories.  This
@@ -16,3 +11,15 @@ config FS_ENCRYPTION
 	  efficient since it avoids caching the encrypted and
 	  decrypted pages in the page cache.  Currently Ext4,
 	  F2FS and UBIFS make use of this feature.
+
+# Filesystems supporting encryption must select this if FS_ENCRYPTION.  This
+# allows the algorithms to be built as modules when all the filesystems are.
+config FS_ENCRYPTION_ALGS
+	tristate
+	select CRYPTO_AES
+	select CRYPTO_CBC
+	select CRYPTO_CTS
+	select CRYPTO_ECB
+	select CRYPTO_HMAC
+	select CRYPTO_SHA512
+	select CRYPTO_XTS
diff --git a/fs/ext4/Kconfig b/fs/ext4/Kconfig
index ef42ab040905..930793456d3a 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_ALGS 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..599fb9194c6a 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_ALGS 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..45d3d207fb99 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_ALGS 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