[PATCH v5 3/8] fscrypt: change fscrypt_dio_supported() to prepare for STATX_DIOALIGN

Eric Biggers
2022-08-27T07:01:40Z

From: Eric Biggers <ebiggers@google.com>

To prepare for STATX_DIOALIGN support, make two changes to
fscrypt_dio_supported().

First, remove the filesystem-block-alignment check and make the
filesystems handle it instead. It previously made sense to have it in
fs/crypto/; however, to support STATX_DIOALIGN the alignment restriction
would have to be returned to filesystems. It ends up being simpler if
filesystems handle this part themselves, especially for f2fs which only
allows fs-block-aligned DIO in the first place.

Second, make fscrypt_dio_supported() work on inodes whose encryption key
hasn't been set up yet, by making it set up the key if needed. This is
required for statx(), since statx() doesn't require a file descriptor.

Reviewed-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Eric Biggers <ebiggers@google.com>
---
fs/crypto/inline_crypt.c | 49 ++++++++++++++++++++--------------------
fs/ext4/file.c | 9 ++++++--
fs/f2fs/f2fs.h | 2 +-
include/linux/fscrypt.h | 7 ++----
4 files changed, 34 insertions(+), 33 deletions(-)

diff --git a/fs/crypto/inline_crypt.c b/fs/crypto/inline_crypt.c
index 90f3e68f166e39..8d4bee5bccbf42 100644
--- a/fs/crypto/inline_crypt.c
+++ b/fs/crypto/inline_crypt.c
@@ -401,46 +401,45 @@ bool fscrypt_mergeable_bio_bh(struct bio *bio,
EXPORT_SYMBOL_GPL(fscrypt_mergeable_bio_bh);

/**
- * fscrypt_dio_supported() - check whether a DIO (direct I/O) request is
- * supported as far as encryption is concerned
- * @iocb: the file and position the I/O is targeting
- * @iter: the I/O data segment(s)
+ * fscrypt_dio_supported() - check whether DIO (direct I/O) is supported on an
+ * inode, as far as encryption is concerned
+ * @inode: the inode in question
*
* Return: %true if there are no encryption constraints that prevent DIO from
* being supported; %false if DIO is unsupported. (Note that in the
* %true case, the filesystem might have other, non-encryption-related
- * constraints that prevent DIO from actually being supported.)
+ * constraints that prevent DIO from actually being supported. Also, on
+ * encrypted files the filesystem is still responsible for only allowing
+ * DIO when requests are filesystem-block-aligned.)
*/
-bool fscrypt_dio_supported(struct kiocb *iocb, struct iov_iter *iter)
+bool fscrypt_dio_supported(struct inode *inode)
{
- const struct inode *inode = file_inode(iocb->ki_filp);
- const unsigned int blocksize = i_blocksize(inode);
+ int err;

/* If the file is unencrypted, no veto from us. */
if (!fscrypt_needs_contents_encryption(inode))
return true;

- /* We only support DIO with inline crypto, not fs-layer crypto. */
- if (!fscrypt_inode_uses_inline_crypto(inode))
- return false;
-
/*
- * Since the granularity of encryption is filesystem blocks, the file
- * position and total I/O length must be aligned to the filesystem block
- * size -- not just to the block device's logical block size as is
- * traditionally the case for DIO on many filesystems.
+ * We only support DIO with inline crypto, not fs-layer crypto.
*
- * We require that the user-provided memory buffers be filesystem block
- * aligned too. It is simpler to have a single alignment value required
- * for all properties of the I/O, as is normally the case for DIO.
- * Also, allowing less aligned buffers would imply that data units could
- * cross bvecs, which would greatly complicate the I/O stack, which
- * assumes that bios can be split at any bvec boundary.
+ * To determine whether the inode is using inline crypto, we have to set
+ * up the key if it wasn't already done. This is because in the current
+ * design of fscrypt, the decision of whether to use inline crypto or
+ * not isn't made until the inode's encryption key is being set up. In
+ * the DIO read/write case, the key will always be set up already, since
+ * the file will be open. But in the case of statx(), the key might not
+ * be set up yet, as the file might not have been opened yet.
*/
- if (!IS_ALIGNED(iocb->ki_pos | iov_iter_alignment(iter), blocksize))
+ err = fscrypt_require_key(inode);
+ if (err) {
+ /*
+ * Key unavailable or couldn't be set up. This edge case isn't
+ * worth worrying about; just report that DIO is unsupported.
+ */
return false;
-
- return true;
+ }
+ return fscrypt_inode_uses_inline_crypto(inode);
}
EXPORT_SYMBOL_GPL(fscrypt_dio_supported);

diff --git a/fs/ext4/file.c b/fs/ext4/file.c
index 109d07629f81fb..26d7426208970d 100644
--- a/fs/ext4/file.c
+++ b/fs/ext4/file.c
@@ -40,8 +40,13 @@ static bool ext4_dio_supported(struct kiocb *iocb, struct iov_iter *iter)
{
struct inode *inode = file_inode(iocb->ki_filp);

- if (!fscrypt_dio_supported(iocb, iter))
- return false;
+ if (IS_ENCRYPTED(inode)) {
+ if (!fscrypt_dio_supported(inode))
+ return false;
+ if (!IS_ALIGNED(iocb->ki_pos | iov_iter_alignment(iter),
+ i_blocksize(inode)))
+ return false;
+ }
if (fsverity_active(inode))
return false;
if (ext4_should_journal_data(inode))
diff --git a/fs/f2fs/f2fs.h b/fs/f2fs/f2fs.h
index 3c7cdb70fe2efc..0759da1919f4ad 100644
--- a/fs/f2fs/f2fs.h
+++ b/fs/f2fs/f2fs.h
@@ -4498,7 +4498,7 @@ static inline bool f2fs_force_buffered_io(struct inode *inode,
struct f2fs_sb_info *sbi = F2FS_I_SB(inode);
int rw = iov_iter_rw(iter);

- if (!fscrypt_dio_supported(iocb, iter))
+ if (!fscrypt_dio_supported(inode))
return true;
if (fsverity_active(inode))
return true;
diff --git a/include/linux/fscrypt.h b/include/linux/fscrypt.h
index 7d2f1e0f23b1fe..13598859d5b394 100644
--- a/include/linux/fscrypt.h
+++ b/include/linux/fscrypt.h
@@ -768,7 +768,7 @@ bool fscrypt_mergeable_bio(struct bio *bio, const struct inode *inode,
bool fscrypt_mergeable_bio_bh(struct bio *bio,
const struct buffer_head *next_bh);

-bool fscrypt_dio_supported(struct kiocb *iocb, struct iov_iter *iter);
+bool fscrypt_dio_supported(struct inode *inode);

u64 fscrypt_limit_io_blocks(const struct inode *inode, u64 lblk, u64 nr_blocks);

@@ -801,11 +801,8 @@ static inline bool fscrypt_mergeable_bio_bh(struct bio *bio,
return true;
}

-static inline bool fscrypt_dio_supported(struct kiocb *iocb,
- struct iov_iter *iter)
+static inline bool fscrypt_dio_supported(struct inode *inode)
{
- const struct inode *inode = file_inode(iocb->ki_filp);
-
return !fscrypt_needs_contents_encryption(inode);
}

--
2.37.2