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 <chan...@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 63d73b360f1d..cadf50f9503f 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)
 {
        return index < (i_size_read(inode) + PAGE_SIZE - 1) >> PAGE_SHIFT;
@@ -1438,6 +1455,7 @@ 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



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