iomap: support direct I/O with fscrypt using blk-crypto

Encrypted files traditionally haven't supported DIO, due to the need to
encrypt/decrypt the data.  However, when the encryption is implemented
using inline encryption (blk-crypto) instead of the traditional
filesystem-layer encryption, it is straightforward to support DIO.

Add support for this to the iomap DIO implementation by calling
fscrypt_set_bio_crypt_ctx() to set encryption contexts on the bios.

Don't check for the rare case where a DUN (crypto data unit number)
discontiguity creates a boundary that bios must not cross.  Instead,
filesystems are expected to handle this in ->iomap_begin() by limiting
the length of the mapping so that iomap doesn't have to worry about it.

Co-developed-by: Satya Tangirala <satyat@google.com>
Signed-off-by: Satya Tangirala <satyat@google.com>
Acked-by: Darrick J. Wong <djwong@kernel.org>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Link: https://lore.kernel.org/r/20220128233940.79464-3-ebiggers@kernel.org
Signed-off-by: Eric Biggers <ebiggers@google.com>

diff --git a/fs/iomap/direct-io.c b/fs/iomap/direct-io.c
index 03ea367df19a479a99b062860ee207b0b049a432..20325b3926fa3eee0676cdb11cdc5e564699ca53 100644 (file)
--- a/fs/iomap/direct-io.c
+++ b/fs/iomap/direct-io.c
@@ -6,6 +6,7 @@
 #include <linux/module.h>
 #include <linux/compiler.h>
 #include <linux/fs.h>
+#include <linux/fscrypt.h>
 #include <linux/pagemap.h>
 #include <linux/iomap.h>
 #include <linux/backing-dev.h>
@@ -179,11 +180,14 @@ static void iomap_dio_bio_end_io(struct bio *bio)
 static void iomap_dio_zero(const struct iomap_iter *iter, struct iomap_dio *dio,
                loff_t pos, unsigned len)
 {
+       struct inode *inode = file_inode(dio->iocb->ki_filp);
        struct page *page = ZERO_PAGE(0);
        int flags = REQ_SYNC | REQ_IDLE;
        struct bio *bio;
 
        bio = bio_alloc(GFP_KERNEL, 1);
+       fscrypt_set_bio_crypt_ctx(bio, inode, pos >> inode->i_blkbits,
+                                 GFP_KERNEL);
        bio_set_dev(bio, iter->iomap.bdev);
        bio->bi_iter.bi_sector = iomap_sector(&iter->iomap, pos);
        bio->bi_private = dio;
@@ -310,6 +314,8 @@ static loff_t iomap_dio_bio_iter(const struct iomap_iter *iter,
                }
 
                bio = bio_alloc(GFP_KERNEL, nr_pages);
+               fscrypt_set_bio_crypt_ctx(bio, inode, pos >> inode->i_blkbits,
+                                         GFP_KERNEL);
                bio_set_dev(bio, iomap->bdev);
                bio->bi_iter.bi_sector = iomap_sector(iomap, pos);
                bio->bi_write_hint = dio->iocb->ki_hint;