[PATCH v3 06/28] fsverity: add drop_page() callout

[Andrey Albershteyn <aalbersh@redhat.com>]

Allow filesystem to make additional processing on verified pages
instead of just dropping a reference. This will be used by XFS for
internal buffer cache manipulation in further patches. The btrfs,
ext4, and f2fs just drop the reference.

Signed-off-by: Andrey Albershteyn <aalbersh@redhat.com>
---
 fs/verity/read_metadata.c |  4 ++--
 fs/verity/verify.c        |  6 +++---
 include/linux/fsverity.h  | 33 +++++++++++++++++++++++++++++++++
 3 files changed, 38 insertions(+), 5 deletions(-)

diff --git a/fs/verity/read_metadata.c b/fs/verity/read_metadata.c
index f58432772d9e..8bd4b29a9a95 100644
--- a/fs/verity/read_metadata.c
+++ b/fs/verity/read_metadata.c
@@ -56,12 +56,12 @@ static int fsverity_read_merkle_tree(struct inode *inode,
 		virt = kmap_local_page(page);
 		if (copy_to_user(buf, virt + offs_in_page, bytes_to_copy)) {
 			kunmap_local(virt);
-			put_page(page);
+			fsverity_drop_page(inode, page);
 			err = -EFAULT;
 			break;
 		}
 		kunmap_local(virt);
-		put_page(page);
+		fsverity_drop_page(inode, page);
 
 		retval += bytes_to_copy;
 		buf += bytes_to_copy;
diff --git a/fs/verity/verify.c b/fs/verity/verify.c
index 904ccd7e8e16..2fe7bd57b16e 100644
--- a/fs/verity/verify.c
+++ b/fs/verity/verify.c
@@ -183,7 +183,7 @@ verify_data_block(struct inode *inode, struct fsverity_info *vi,
 			memcpy(_want_hash, haddr + hoffset, hsize);
 			want_hash = _want_hash;
 			kunmap_local(haddr);
-			put_page(hpage);
+			fsverity_drop_page(inode, hpage);
 			goto descend;
 		}
 		hblocks[level].page = hpage;
@@ -218,7 +218,7 @@ verify_data_block(struct inode *inode, struct fsverity_info *vi,
 		memcpy(_want_hash, haddr + hoffset, hsize);
 		want_hash = _want_hash;
 		kunmap_local(haddr);
-		put_page(hpage);
+		fsverity_drop_page(inode, hpage);
 	}
 
 	/* Finally, verify the data block. */
@@ -237,7 +237,7 @@ verify_data_block(struct inode *inode, struct fsverity_info *vi,
 error:
 	for (; level > 0; level--) {
 		kunmap_local(hblocks[level - 1].addr);
-		put_page(hblocks[level - 1].page);
+		fsverity_drop_page(inode, hblocks[level - 1].page);
 	}
 	return false;
 }
diff --git a/include/linux/fsverity.h b/include/linux/fsverity.h
index 1eb7eae580be..6514ed6b09b4 100644
--- a/include/linux/fsverity.h
+++ b/include/linux/fsverity.h
@@ -120,6 +120,16 @@ struct fsverity_operations {
 	 */
 	int (*write_merkle_tree_block)(struct inode *inode, const void *buf,
 				       u64 pos, unsigned int size);
+
+	/**
+	 * Release the reference to a Merkle tree page
+	 *
+	 * @page: the page to release
+	 *
+	 * This is called when fs-verity is done with a page obtained with
+	 * ->read_merkle_tree_page().
+	 */
+	void (*drop_page)(struct page *page);
 };
 
 #ifdef CONFIG_FS_VERITY
@@ -174,6 +184,24 @@ bool fsverity_verify_blocks(struct folio *folio, size_t len, size_t offset);
 void fsverity_verify_bio(struct bio *bio);
 void fsverity_enqueue_verify_work(struct work_struct *work);
 
+/**
+ * fsverity_drop_page() - drop page obtained with ->read_merkle_tree_page()
+ * @inode: inode in use for verification or metadata reading
+ * @page: page to be dropped
+ *
+ * Generic put_page() method. Calls out back to filesystem if ->drop_page() is
+ * set, otherwise just drops the reference to a page.
+ *
+ */
+static inline void fsverity_drop_page(struct inode *inode, struct page *page)
+{
+	if (inode->i_sb->s_vop->drop_page)
+		inode->i_sb->s_vop->drop_page(page);
+	else
+		put_page(page);
+}
+
+
 #else /* !CONFIG_FS_VERITY */
 
 static inline struct fsverity_info *fsverity_get_info(const struct inode *inode)
@@ -251,6 +279,11 @@ static inline void fsverity_enqueue_verify_work(struct work_struct *work)
 	WARN_ON_ONCE(1);
 }
 
+static inline void fsverity_drop_page(struct inode *inode, struct page *page)
+{
+	WARN_ON_ONCE(1);
+}
+
 #endif	/* !CONFIG_FS_VERITY */
 
 static inline bool fsverity_verify_folio(struct folio *folio)
-- 
2.40.1