[v9,3/9] fscrypt: add functions for direct I/O support

Commit Message

Satya Tangirala June 4, 2021, 9:09 p.m. UTC

From: Eric Biggers <[e-mail]>

Introduce fscrypt_dio_supported() to check whether a direct I/O request
is unsupported due to encryption constraints.

Also introduce fscrypt_limit_io_blocks() to limit how many blocks can be
added to a bio being prepared for direct I/O. This is needed for
filesystems that use the iomap direct I/O implementation to avoid DUN
wraparound in the middle of a bio (which is possible with the
IV_INO_LBLK_32 IV generation method). Elsewhere fscrypt_mergeable_bio()
is used for this, but iomap operates on logical ranges directly, so
filesystems using iomap won't have a chance to call fscrypt_mergeable_bio()
on every block added to a bio. So we need this function which limits a
logical range in one go.

Signed-off-by: Eric Biggers <[e-mail]>
Co-developed-by: Satya Tangirala <[e-mail]>
Signed-off-by: Satya Tangirala <[e-mail]>
---
 fs/crypto/crypto.c       |  8 +++++
 fs/crypto/inline_crypt.c | 75 ++++++++++++++++++++++++++++++++++++++++
 include/linux/fscrypt.h  | 18 ++++++++++
 3 files changed, 101 insertions(+)

Comments

Eric Biggers July 23, 2021, 8:42 p.m. UTC | #1

On Fri, Jun 04, 2021 at 09:09:02PM +0000, Satya Tangirala wrote:
> +bool fscrypt_dio_supported(struct kiocb *iocb, struct iov_iter *iter)
> +{
> +	const struct inode *inode = file_inode(iocb->ki_filp);
> +	const unsigned int blocksize = i_blocksize(inode);
> +
> +	/* If the file is unencrypted, no veto from us. */
> +	if (!fscrypt_needs_contents_encryption(inode))
> +		return true;
> +
> +	/* We only support direct I/O 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 I/O
> +	 * must be block aligned -- not just disk sector aligned.
> +	 */
> +	if (!IS_ALIGNED(iocb->ki_pos | iov_iter_count(iter), blocksize))
> +		return false;

The above comment should make it clear that "block aligned" here intentionally
applies to just the position and total length, not to the individual data
buffers, for which only disk sector alignment is required.

- Eric

Patch

diff --git a/fs/crypto/crypto.c b/fs/crypto/crypto.c
index 4ef3f714046a..4fcca79f39ae 100644
--- a/fs/crypto/crypto.c
+++ b/fs/crypto/crypto.c
@@ -69,6 +69,14 @@  void fscrypt_free_bounce_page(struct page *bounce_page)
 }
 EXPORT_SYMBOL(fscrypt_free_bounce_page);
 
+/*
+ * Generate the IV for the given logical block number within the given file.
+ * For filenames encryption, lblk_num == 0.
+ *
+ * Keep this in sync with fscrypt_limit_io_blocks().  fscrypt_limit_io_blocks()
+ * needs to know about any IV generation methods where the low bits of IV don't
+ * simply contain the lblk_num (e.g., IV_INO_LBLK_32).
+ */
 void fscrypt_generate_iv(union fscrypt_iv *iv, u64 lblk_num,
 			 const struct fscrypt_info *ci)
 {
diff --git a/fs/crypto/inline_crypt.c b/fs/crypto/inline_crypt.c
index c57bebfa48fe..a7ce650fbd3b 100644
--- a/fs/crypto/inline_crypt.c
+++ b/fs/crypto/inline_crypt.c
@@ -17,6 +17,7 @@ 
 #include <linux/buffer_head.h>
 #include <linux/sched/mm.h>
 #include <linux/slab.h>
+#include <linux/uio.h>
 
 #include "fscrypt_private.h"
 
@@ -363,3 +364,77 @@  bool fscrypt_mergeable_bio_bh(struct bio *bio,
 	return fscrypt_mergeable_bio(bio, inode, next_lblk);
 }
 EXPORT_SYMBOL_GPL(fscrypt_mergeable_bio_bh);
+
+/**
+ * fscrypt_dio_supported() - check whether a direct I/O request is unsupported
+ *			     due to encryption constraints
+ * @iocb: the file and position the I/O is targeting
+ * @iter: the I/O data segment(s)
+ *
+ * Return: true if direct I/O is supported
+ */
+bool fscrypt_dio_supported(struct kiocb *iocb, struct iov_iter *iter)
+{
+	const struct inode *inode = file_inode(iocb->ki_filp);
+	const unsigned int blocksize = i_blocksize(inode);
+
+	/* If the file is unencrypted, no veto from us. */
+	if (!fscrypt_needs_contents_encryption(inode))
+		return true;
+
+	/* We only support direct I/O 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 I/O
+	 * must be block aligned -- not just disk sector aligned.
+	 */
+	if (!IS_ALIGNED(iocb->ki_pos | iov_iter_count(iter), blocksize))
+		return false;
+
+	return true;
+}
+EXPORT_SYMBOL_GPL(fscrypt_dio_supported);
+
+/**
+ * fscrypt_limit_io_blocks() - limit I/O blocks to avoid discontiguous DUNs
+ * @inode: the file on which I/O is being done
+ * @lblk: the block at which the I/O is being started from
+ * @nr_blocks: the number of blocks we want to submit starting at @lblk
+ *
+ * Determine the limit to the number of blocks that can be submitted in the bio
+ * targeting @lblk without causing a data unit number (DUN) discontinuity.
+ *
+ * This is normally just @nr_blocks, as normally the DUNs just increment along
+ * with the logical blocks.  (Or the file is not encrypted.)
+ *
+ * In rare cases, fscrypt can be using an IV generation method that allows the
+ * DUN to wrap around within logically continuous blocks, and that wraparound
+ * will occur.  If this happens, a value less than @nr_blocks will be returned
+ * so that the wraparound doesn't occur in the middle of the bio.
+ *
+ * Return: the actual number of blocks that can be submitted
+ */
+u64 fscrypt_limit_io_blocks(const struct inode *inode, u64 lblk, u64 nr_blocks)
+{
+	const struct fscrypt_info *ci = inode->i_crypt_info;
+	u32 dun;
+
+	if (!fscrypt_inode_uses_inline_crypto(inode))
+		return nr_blocks;
+
+	if (nr_blocks <= 1)
+		return nr_blocks;
+
+	if (!(fscrypt_policy_flags(&ci->ci_policy) &
+	      FSCRYPT_POLICY_FLAG_IV_INO_LBLK_32))
+		return nr_blocks;
+
+	/* With IV_INO_LBLK_32, the DUN can wrap around from U32_MAX to 0. */
+
+	dun = ci->ci_hashed_ino + lblk;
+
+	return min_t(u64, nr_blocks, (u64)U32_MAX + 1 - dun);
+}
+EXPORT_SYMBOL_GPL(fscrypt_limit_io_blocks);
diff --git a/include/linux/fscrypt.h b/include/linux/fscrypt.h
index 2ea1387bb497..d8dde02aee82 100644
--- a/include/linux/fscrypt.h
+++ b/include/linux/fscrypt.h
@@ -609,6 +609,10 @@  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);
+
+u64 fscrypt_limit_io_blocks(const struct inode *inode, u64 lblk, u64 nr_blocks);
+
 #else /* CONFIG_FS_ENCRYPTION_INLINE_CRYPT */
 
 static inline bool __fscrypt_inode_uses_inline_crypto(const struct inode *inode)
@@ -637,6 +641,20 @@  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)
+{
+	const struct inode *inode = file_inode(iocb->ki_filp);
+
+	return !fscrypt_needs_contents_encryption(inode);
+}
+
+static inline u64 fscrypt_limit_io_blocks(const struct inode *inode, u64 lblk,
+					  u64 nr_blocks)
+{
+	return nr_blocks;
+}
 #endif /* !CONFIG_FS_ENCRYPTION_INLINE_CRYPT */
 
 /**