[RFC PATCH 07/10] fsverity: Add call back to determine readpage limit

[Chandan Rajendra <chandan@linux.ibm.com>]

Ext4 and F2FS store verity metadata beyond i_size. This commit adds a
call back pointer to "struct fsverity_operations" which helps in
determining the the real file size limit upto which data can be read
from the file.

This call back will be required in order to get do_mpage_readpage()
to read files having verity metadata appended beyond i_size.

Signed-off-by: Chandan Rajendra <chandan@linux.ibm.com>
---
 fs/ext4/super.c          | 18 ++++++++++++++++++
 include/linux/fsverity.h |  1 +
 2 files changed, 19 insertions(+)

diff --git a/fs/ext4/super.c b/fs/ext4/super.c
index 2d7781ab6824..4493ddc357c6 100644
--- a/fs/ext4/super.c
+++ b/fs/ext4/super.c
@@ -1428,6 +1428,23 @@ static struct page *ext4_read_verity_metadata_page(struct inode *inode,
 	return read_mapping_page(inode->i_mapping, index, NULL);
 }
 
+static loff_t ext4_readpage_limit(struct inode *inode)
+{
+#ifdef CONFIG_FS_VERITY
+	if (IS_VERITY(inode)) {
+		if (inode->i_verity_info)
+			/* limit to end of metadata region */
+			return fsverity_full_i_size(inode);
+		/*
+		 * fsverity_info is currently being set up and no user reads are
+		 * allowed yet.  It's easiest to just not enforce a limit yet.
+		 */
+		return inode->i_sb->s_maxbytes;
+	}
+#endif
+	return i_size_read(inode);
+}
+
 static bool ext4_verity_required(struct inode *inode, pgoff_t index)
 {
 	if (index < ((i_size_read(inode) + PAGE_SIZE - 1) >> PAGE_SHIFT))
@@ -1441,6 +1458,7 @@ static const struct fsverity_operations ext4_verityops = {
 	.get_metadata_end	= ext4_get_verity_metadata_end,
 	.read_metadata_page	= ext4_read_verity_metadata_page,
 	.verity_required	= ext4_verity_required,
+	.readpage_limit		= ext4_readpage_limit,
 };
 #endif /* CONFIG_FS_VERITY */
 
diff --git a/include/linux/fsverity.h b/include/linux/fsverity.h
index b83712d6c79a..fc8113acbbfe 100644
--- a/include/linux/fsverity.h
+++ b/include/linux/fsverity.h
@@ -19,6 +19,7 @@ struct fsverity_operations {
 	int (*get_metadata_end)(struct inode *inode, loff_t *metadata_end_ret);
 	struct page *(*read_metadata_page)(struct inode *inode, pgoff_t index);
 	bool (*verity_required)(struct inode *inode, pgoff_t index);
+	loff_t (*readpage_limit)(struct inode *inode);
 };
 
 #ifdef CONFIG_FS_VERITY
-- 
2.19.1