fscrypt: Always use blk-crypto for contents on block-based filesystems

For encrypting and decrypting file contents on block-based filesystems
(i.e., ext4 and f2fs, but not ceph and ubifs), always use blk-crypto
instead of fs-layer crypto (direct use of crypto_skcipher).

Since the blk-crypto API provides a fallback to CPU-based encryption,
it's all that's needed on block-based filesystems.  The support for two
alternative block-based file contents encryption implementations,
fs-layer and blk-crypto, existed mainly for historical reasons, as the
fs-layer path came first.  Some of it is also still needed for the
non-block-based filesystems, but a lot of it isn't.

Removing the duplicate fs-layer code paths greatly simplifies the code,
most of which is done in later commits.

Specific implementation details:

- SB_INLINECRYPT now controls whether blk_crypto_config::allow_hw is set
  to true, instead of whether blk-crypto is used at all.  The effect is
  that the semantics are preserved: the inlinecrypt mount option selects
  the use of inline encryption hardware instead of the CPU.

- Set up a blk_crypto_key iff the file is a regular file on a
  block-based filesystem.  To determine whether the filesystem is
  block-based, add a bit fscrypt_operations::is_block_based.

- Remove fscrypt_select_encryption_impl().  Move the logging logic that
  was previously there into fscrypt_prepare_inline_crypt_key().  Note
  that blk_crypto_config_supported() is no longer needed.

Reviewed-by: Christoph Hellwig <hch@lst.de>
Link: https://patch.msgid.link/20260713023708.9245-6-ebiggers@kernel.org
Signed-off-by: Eric Biggers <ebiggers@kernel.org>

1 files changed, 1 insertions, 0 deletions

diff --git a/fs/ext4/crypto.c b/fs/ext4/crypto.c
index f41f320f4437..6b809ac80ef7 100644
--- a/fs/ext4/crypto.c
+++ b/fs/ext4/crypto.c
@@ -236,6 +236,7 @@ static bool ext4_has_stable_inodes(struct super_block *sb)
 const struct fscrypt_operations ext4_cryptops = {
 	.inode_info_offs	= (int)offsetof(struct ext4_inode_info, i_crypt_info) -
 				  (int)offsetof(struct ext4_inode_info, vfs_inode),
+	.is_block_based		= 1,
 	.needs_bounce_pages	= 1,
 	.has_32bit_inodes	= 1,
 	.supports_subblock_data_units = 1,