[PATCH v2 06/23] fsverity: add drop_page() callout

[Andrey Albershteyn]

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 at redhat.com>
---
 fs/btrfs/verity.c         | 12 ++++++++++++
 fs/ext4/verity.c          |  6 ++++++
 fs/f2fs/verity.c          |  6 ++++++
 fs/verity/read_metadata.c |  4 ++--
 fs/verity/verify.c        |  6 +++---
 include/linux/fsverity.h  | 10 ++++++++++
 6 files changed, 39 insertions(+), 5 deletions(-)

diff --git a/fs/btrfs/verity.c b/fs/btrfs/verity.c
index c5ff16f9e9fa..4c2c09204bb4 100644
--- a/fs/btrfs/verity.c
+++ b/fs/btrfs/verity.c
@@ -804,10 +804,22 @@ static int btrfs_write_merkle_tree_block(struct inode *inode, const void *buf,
 			       pos, buf, size);
 }
 
+/*
+ * fsverity op that releases the reference obtained by ->read_merkle_tree_page()
+ *
+ * @page:  reference to the page which can be released
+ *
+ */
+static void btrfs_drop_page(struct page *page)
+{
+	put_page(page);
+}
+
 const struct fsverity_operations btrfs_verityops = {
 	.begin_enable_verity     = btrfs_begin_enable_verity,
 	.end_enable_verity       = btrfs_end_enable_verity,
 	.get_verity_descriptor   = btrfs_get_verity_descriptor,
 	.read_merkle_tree_page   = btrfs_read_merkle_tree_page,
 	.write_merkle_tree_block = btrfs_write_merkle_tree_block,
+	.drop_page		 = &btrfs_drop_page,
 };
diff --git a/fs/ext4/verity.c b/fs/ext4/verity.c
index e4da1704438e..35a2feb6fd68 100644
--- a/fs/ext4/verity.c
+++ b/fs/ext4/verity.c
@@ -388,10 +388,16 @@ static int ext4_write_merkle_tree_block(struct inode *inode, const void *buf,
 	return pagecache_write(inode, buf, size, pos);
 }
 
+static void ext4_drop_page(struct page *page)
+{
+	put_page(page);
+}
+
 const struct fsverity_operations ext4_verityops = {
 	.begin_enable_verity	= ext4_begin_enable_verity,
 	.end_enable_verity	= ext4_end_enable_verity,
 	.get_verity_descriptor	= ext4_get_verity_descriptor,
 	.read_merkle_tree_page	= ext4_read_merkle_tree_page,
 	.write_merkle_tree_block = ext4_write_merkle_tree_block,
+	.drop_page		= &ext4_drop_page,
 };
diff --git a/fs/f2fs/verity.c b/fs/f2fs/verity.c
index 4fc95f353a7a..019c7a6c6bcf 100644
--- a/fs/f2fs/verity.c
+++ b/fs/f2fs/verity.c
@@ -283,10 +283,16 @@ static int f2fs_write_merkle_tree_block(struct inode *inode, const void *buf,
 	return pagecache_write(inode, buf, size, pos);
 }
 
+static void f2fs_drop_page(struct page *page)
+{
+	put_page(page);
+}
+
 const struct fsverity_operations f2fs_verityops = {
 	.begin_enable_verity	= f2fs_begin_enable_verity,
 	.end_enable_verity	= f2fs_end_enable_verity,
 	.get_verity_descriptor	= f2fs_get_verity_descriptor,
 	.read_merkle_tree_page	= f2fs_read_merkle_tree_page,
 	.write_merkle_tree_block = f2fs_write_merkle_tree_block,
+	.drop_page		= &f2fs_drop_page,
 };
diff --git a/fs/verity/read_metadata.c b/fs/verity/read_metadata.c
index 2aefc5565152..cab1612bf4a3 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);
+			inode->i_sb->s_vop->drop_page(page);
 			err = -EFAULT;
 			break;
 		}
 		kunmap_local(virt);
-		put_page(page);
+		inode->i_sb->s_vop->drop_page(page);
 
 		retval += bytes_to_copy;
 		buf += bytes_to_copy;
diff --git a/fs/verity/verify.c b/fs/verity/verify.c
index f50e3b5b52c9..c2fc4c86af34 100644
--- a/fs/verity/verify.c
+++ b/fs/verity/verify.c
@@ -210,7 +210,7 @@ verify_data_block(struct inode *inode, struct fsverity_info *vi,
 		if (is_hash_block_verified(vi, hpage, hblock_idx)) {
 			memcpy_from_page(_want_hash, hpage, hoffset, hsize);
 			want_hash = _want_hash;
-			put_page(hpage);
+			inode->i_sb->s_vop->drop_page(hpage);
 			goto descend;
 		}
 		hblocks[level].page = hpage;
@@ -248,7 +248,7 @@ verify_data_block(struct inode *inode, struct fsverity_info *vi,
 			SetPageChecked(hpage);
 		memcpy_from_page(_want_hash, hpage, hoffset, hsize);
 		want_hash = _want_hash;
-		put_page(hpage);
+		inode->i_sb->s_vop->drop_page(hpage);
 	}
 
 	/* Finally, verify the data block. */
@@ -259,7 +259,7 @@ verify_data_block(struct inode *inode, struct fsverity_info *vi,
 	err = cmp_hashes(vi, want_hash, real_hash, data_pos, -1);
 out:
 	for (; level > 0; level--)
-		put_page(hblocks[level - 1].page);
+		inode->i_sb->s_vop->drop_page(hblocks[level - 1].page);
 
 	return err == 0;
 }
diff --git a/include/linux/fsverity.h b/include/linux/fsverity.h
index 6d7a4b3ea626..3e923a8e0d6f 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
-- 
2.38.4