[PATCH v15 02/25] fsverity: expose ensure_fsverity_info()

This function will be used by XFS's scrub to force fsverity activation,
therefore, to read fsverity context.

Reviewed-by: Darrick J. Wong <[email protected]>
Acked-by: Eric Biggers <[email protected]>
Signed-off-by: Andrey Albershteyn <[email protected]>
Reviewed-by: Christoph Hellwig <[email protected]>
---
 fs/verity/open.c         | 26 ++++++++++++++++++++++++--
 include/linux/fsverity.h |  2 ++
 2 files changed, 26 insertions(+), 2 deletions(-)

diff --git a/fs/verity/open.c b/fs/verity/open.c
index d0c56a7faa3b..4f06697f5bf4 100644
--- a/fs/verity/open.c
+++ b/fs/verity/open.c
@@ -347,7 +347,28 @@ int fsverity_get_descriptor(struct inode *inode,
 	return 0;
 }
 
-static int ensure_verity_info(struct inode *inode)
+/**
+ * fsverity_ensure_verity_info() - cache verity info if it's not already cached
+ * @inode: the inode for which verity info should be cached
+ *
+ * Ensure this inode has verity info attached to it, it's assumed the inode
+ * already has fsverity enabled. Read fsverity descriptor and creates verity
+ * based on that.
+ *
+ * This needs to be called at least once before any of the inode's data
+ * can be verified (and thus read at all) or the inode's fsverity digest
+ * retrieved.  fsverity_file_open() calls this already, which handles
+ * normal file accesses.  If a filesystem does any internal (i.e. not
+ * associated with a file descriptor) reads of the file's data or
+ * fsverity digest, it must call this explicitly before doing so.
+ *
+ * In case filesystem supports both fscrypt and fsverity, this should be called
+ * after fscrypt's encryption key is set up. Otherwise, the fsverity metadata is
+ * still encrypted. See fscrypt_file_open().
+ *
+ * Return: 0 on success, -errno on failure
+ */
+int fsverity_ensure_verity_info(struct inode *inode)
 {
 	struct fsverity_info *vi = fsverity_get_info(inode), *found;
 	struct fsverity_descriptor *desc;
@@ -383,12 +404,13 @@ static int ensure_verity_info(struct inode *inode)
 	kfree(desc);
 	return err;
 }
+EXPORT_SYMBOL_GPL(fsverity_ensure_verity_info);
 
 int __fsverity_file_open(struct inode *inode, struct file *filp)
 {
 	if (filp->f_mode & FMODE_WRITE)
 		return -EPERM;
-	return ensure_verity_info(inode);
+	return fsverity_ensure_verity_info(inode);
 }
 EXPORT_SYMBOL_GPL(__fsverity_file_open);
 
diff --git a/include/linux/fsverity.h b/include/linux/fsverity.h
index 6c467ded9751..3c3250f6f272 100644
--- a/include/linux/fsverity.h
+++ b/include/linux/fsverity.h
@@ -317,6 +317,8 @@ static inline int fsverity_file_open(struct inode *inode, struct file *filp)
 	return 0;
 }
 
+int fsverity_ensure_verity_info(struct inode *inode);
+
 void fsverity_cleanup_inode(struct inode *inode);
 
 struct page *generic_read_merkle_tree_page(struct inode *inode, pgoff_t index);
-- 
2.54.0