fscrypt: allow synchronous bio decryption

Currently, fscrypt provides fscrypt_decrypt_bio_pages() which decrypts a
bio's pages asynchronously, then unlocks them afterwards.  But, this
assumes that decryption is the last "postprocessing step" for the bio,
so it's incompatible with additional postprocessing steps such as
authenticity verification after decryption.

Therefore, rename the existing fscrypt_decrypt_bio_pages() to
fscrypt_enqueue_decrypt_bio().  Then, add fscrypt_decrypt_bio() which
decrypts the pages in the bio synchronously without unlocking the pages,
nor setting them Uptodate; and add fscrypt_enqueue_decrypt_work(), which
enqueues work on the fscrypt_read_workqueue.  The new functions will be
used by filesystems that support both fscrypt and fs-verity.

Signed-off-by: Eric Biggers <ebiggers@google.com>
Signed-off-by: Jaegeuk Kim <jaegeuk@kernel.org>

1 files changed, 22 insertions, 13 deletions

diff --git a/fs/crypto/bio.c b/fs/crypto/bio.c
index 0d5e6a569d58..0959044c5cee 100644
--- a/fs/crypto/bio.c
+++ b/fs/crypto/bio.c
@@ -26,15 +26,8 @@
 #include <linux/namei.h>
 #include "fscrypt_private.h"
 
-/*
- * Call fscrypt_decrypt_page on every single page, reusing the encryption
- * context.
- */
-static void completion_pages(struct work_struct *work)
+static void __fscrypt_decrypt_bio(struct bio *bio, bool done)
 {
-	struct fscrypt_ctx *ctx =
-		container_of(work, struct fscrypt_ctx, r.work);
-	struct bio *bio = ctx->r.bio;
 	struct bio_vec *bv;
 	int i;
 
@@ -46,22 +39,38 @@ static void completion_pages(struct work_struct *work)
 		if (ret) {
 			WARN_ON_ONCE(1);
 			SetPageError(page);
-		} else {
+		} else if (done) {
 			SetPageUptodate(page);
 		}
-		unlock_page(page);
+		if (done)
+			unlock_page(page);
 	}
+}
+
+void fscrypt_decrypt_bio(struct bio *bio)
+{
+	__fscrypt_decrypt_bio(bio, false);
+}
+EXPORT_SYMBOL(fscrypt_decrypt_bio);
+
+static void completion_pages(struct work_struct *work)
+{
+	struct fscrypt_ctx *ctx =
+		container_of(work, struct fscrypt_ctx, r.work);
+	struct bio *bio = ctx->r.bio;
+
+	__fscrypt_decrypt_bio(bio, true);
 	fscrypt_release_ctx(ctx);
 	bio_put(bio);
 }
 
-void fscrypt_decrypt_bio_pages(struct fscrypt_ctx *ctx, struct bio *bio)
+void fscrypt_enqueue_decrypt_bio(struct fscrypt_ctx *ctx, struct bio *bio)
 {
 	INIT_WORK(&ctx->r.work, completion_pages);
 	ctx->r.bio = bio;
-	queue_work(fscrypt_read_workqueue, &ctx->r.work);
+	fscrypt_enqueue_decrypt_work(&ctx->r.work);
 }
-EXPORT_SYMBOL(fscrypt_decrypt_bio_pages);
+EXPORT_SYMBOL(fscrypt_enqueue_decrypt_bio);
 
 void fscrypt_pullback_bio_page(struct page **page, bool restore)
 {