fscrypt: decrypt only the needed blocks in __fscrypt_decrypt_bio()

In __fscrypt_decrypt_bio(), only decrypt the blocks that actually
comprise the bio, rather than assuming blocksize == PAGE_SIZE and
decrypting the entirety of every page used in the bio.

This is in preparation for allowing encryption on ext4 filesystems with
blocksize != PAGE_SIZE.

This is based on work by Chandan Rajendra.

Reviewed-by: Chandan Rajendra <chandan@linux.ibm.com>
Signed-off-by: Eric Biggers <ebiggers@google.com>

1 files changed, 2 insertions, 2 deletions

diff --git a/fs/crypto/bio.c b/fs/crypto/bio.c
index 61da06fda45c..82da2510721f 100644
--- a/fs/crypto/bio.c
+++ b/fs/crypto/bio.c
@@ -33,8 +33,8 @@ static void __fscrypt_decrypt_bio(struct bio *bio, bool done)
 
         bio_for_each_segment_all(bv, bio, iter_all) {
                 struct page *page = bv->bv_page;
-                int ret = fscrypt_decrypt_pagecache_blocks(page, PAGE_SIZE, 0);
-
+                int ret = fscrypt_decrypt_pagecache_blocks(page, bv->bv_len,
+                                                           bv->bv_offset);
                 if (ret)
                         SetPageError(page);
                 else if (done)