fscrypt: Allow fscrypt_decrypt_page() to function with non-writeback pages

Some filesystem might pass pages which do not have page->mapping->host
set to the encrypted inode. We want the caller to explicitly pass the
corresponding inode.
Signed-off-by: David Gstir <david@sigma-star.at>
Signed-off-by: Richard Weinberger <richard@nod.at>
Signed-off-by: Theodore Ts'o <tytso@mit.edu>

fs/crypto/crypto.c

@@ -271,6 +271,7 @@ EXPORT_SYMBOL(fscrypt_encrypt_page);
 
 /**
  * f2crypt_decrypt_page() - Decrypts a page in-place
+ * @inode: The encrypted inode to decrypt.
  * @page:  The page to decrypt. Must be locked.
  *
  * Decrypts page in-place using the ctx encryption context.
@@ -279,12 +280,12 @@ EXPORT_SYMBOL(fscrypt_encrypt_page);
  *
  * Return: Zero on success, non-zero otherwise.
  */
-int fscrypt_decrypt_page(struct page *page)
+int fscrypt_decrypt_page(struct inode *inode, struct page *page)
 {
 	BUG_ON(!PageLocked(page));
 
-	return do_page_crypto(page->mapping->host,
-			FS_DECRYPT, page->index, page, page, GFP_NOFS);
+	return do_page_crypto(inode, FS_DECRYPT, page->index, page, page,
+			GFP_NOFS);
 }
 EXPORT_SYMBOL(fscrypt_decrypt_page);
 
@@ -419,7 +420,7 @@ static void completion_pages(struct work_struct *work)
 
 	bio_for_each_segment_all(bv, bio, i) {
 		struct page *page = bv->bv_page;
-		int ret = fscrypt_decrypt_page(page);
+		int ret = fscrypt_decrypt_page(page->mapping->host, page);
 
 		if (ret) {
 			WARN_ON_ONCE(1);

fs/ext4/inode.c

@@ -1166,7 +1166,7 @@ static int ext4_block_write_begin(struct page *page, loff_t pos, unsigned len,
 	if (unlikely(err))
 		page_zero_new_buffers(page, from, to);
 	else if (decrypt)
-		err = fscrypt_decrypt_page(page);
+		err = fscrypt_decrypt_page(page->mapping->host, page);
 	return err;
 }
 #endif
@@ -3743,7 +3743,8 @@ static int __ext4_block_zero_page_range(handle_t *handle,
 			/* We expect the key to be set. */
 			BUG_ON(!fscrypt_has_encryption_key(inode));
 			BUG_ON(blocksize != PAGE_SIZE);
-			WARN_ON_ONCE(fscrypt_decrypt_page(page));
+			WARN_ON_ONCE(fscrypt_decrypt_page(page->mapping->host,
+						page));
 		}
 	}
 	if (ext4_should_journal_data(inode)) {

include/linux/fscrypto.h

@@ -249,7 +249,7 @@ int fscrypt_initialize(void);
 extern struct fscrypt_ctx *fscrypt_get_ctx(struct inode *, gfp_t);
 extern void fscrypt_release_ctx(struct fscrypt_ctx *);
 extern struct page *fscrypt_encrypt_page(struct inode *, struct page *, gfp_t);
-extern int fscrypt_decrypt_page(struct page *);
+extern int fscrypt_decrypt_page(struct inode *, struct page *);
 extern void fscrypt_decrypt_bio_pages(struct fscrypt_ctx *, struct bio *);
 extern void fscrypt_pullback_bio_page(struct page **, bool);
 extern void fscrypt_restore_control_page(struct page *);
@@ -298,7 +298,8 @@ static inline struct page *fscrypt_notsupp_encrypt_page(struct inode *i,
 	return ERR_PTR(-EOPNOTSUPP);
 }
 
-static inline int fscrypt_notsupp_decrypt_page(struct page *p)
+static inline int fscrypt_notsupp_decrypt_page(struct inode *i,
+						struct page *p)
 {
 	return -EOPNOTSUPP;
 }