statx: Reserve the top bit of the mask for future struct expansion

Reserve the top bit of the mask for future expansion of the statx struct
and give an error if statx() sees it set.  All the other bits are ignored
if we see them set but don't support the bit; we just clear the bit in the
returned mask.

Signed-off-by: David Howells <dhowells@redhat.com>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>

1 files changed, 2 insertions, 0 deletions

diff --git a/fs/stat.c b/fs/stat.c
index ab27f28..0c7e6cd 100644
--- a/fs/stat.c
+++ b/fs/stat.c
@@ -562,6 +562,8 @@ SYSCALL_DEFINE5(statx,
 	struct kstat stat;
 	int error;
 
+	if (mask & STATX__RESERVED)
+		return -EINVAL;
 	if ((flags & AT_STATX_SYNC_TYPE) == AT_STATX_SYNC_TYPE)
 		return -EINVAL;