[PATCH v2 1/5] fsverity: strip FS_VERITY_FL from FS_IOC_SETFLAGS

[Andrey Albershteyn <aalbersh@kernel.org>]

The common use of FS_IOC_GETFLAGS/SETFLAGS is get-modify-set loop.
Filesystems could return verity status with GETFLAGS, attempting to then
pass FS_VERITY_FL to SETFLAGS is not allowed.

The ext4 and f2fs already treat FS_VERITY_FL in the set path as no-op,
however, BTRFS returns -EOPNOTSUPP. So, the modification of other flags
doesn't work on BTRFS for fsverity inodes.

Fix it for BTRFS and anyone else, the ext4 and f2fs masking becomes
no-op. The file_get/setattr() path is fine here as this flag is cleared
right before fileattr_set_prepare(). The future fsverity support in XFS
would also need it.

Cc: Boris Burkov <boris@bur.io>
Cc: David Sterba <dsterba@suse.com>
Fixes: 146054090b08 ("btrfs: initial fsverity support")
Signed-off-by: Andrey Albershteyn <aalbersh@kernel.org>
---
 fs/file_attr.c | 10 ++++++++++
 1 file changed, 10 insertions(+)

diff --git a/fs/file_attr.c b/fs/file_attr.c
index 833e03810b24..b43977d5f8e0 100644
--- a/fs/file_attr.c
+++ b/fs/file_attr.c
@@ -199,6 +199,16 @@ static int fileattr_set_prepare(struct inode *inode,
 	if (err)
 		return err;
 
+	/*
+	 * verity is settable only via FS_IOC_ENABLE_VERITY; never through
+	 * fileattr
+	 *
+	 * Treat it as a no-op so the FS_IOC_GETFLAGS/SETFLAGS round-trip
+	 * doesn't break for other flags
+	 */
+	fa->flags &= ~FS_VERITY_FL;
+	fa->fsx_xflags &= ~FS_XFLAG_VERITY;
+
 	/*
 	 * Project Quota ID state is only allowed to change from within the init
 	 * namespace. Enforce that restriction only if we are trying to change
-- 
2.54.0