4.4-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Vivek Goyal <vgoyal@redhat.com>

commit 07a2daab49c549a37b5b744cbebb6e3f445f12bc upstream.

Right now when a new overlay inode is created, we initialize overlay
inode's ->i_mode from underlying inode ->i_mode but we retain only
file type bits (S_IFMT) and discard permission bits.

This patch changes it and retains permission bits too. This should allow
overlay to do permission checks on overlay inode itself in task context.

[SzM] It also fixes clearing suid/sgid bits on write.

Signed-off-by: Vivek Goyal <vgoyal@redhat.com>
Reported-by: Eryu Guan <redacted>
Signed-off-by: Miklos Szeredi <redacted>
Fixes: 4bacc9c9234c ("overlayfs: Make f_path always point to the overlay and f_inode to the underlay")
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

---
 fs/overlayfs/inode.c     |    3 +--
 fs/overlayfs/overlayfs.h |    1 +
 2 files changed, 2 insertions(+), 2 deletions(-)

--- a/fs/overlayfs/inode.c
+++ b/fs/overlayfs/inode.c

@@ -412,12 +412,11 @@ struct inode *ovl_new_inode(struct super
 	if (!inode)
 		return NULL;
 
-	mode &= S_IFMT;
-
 	inode->i_ino = get_next_ino();
 	inode->i_mode = mode;
 	inode->i_flags |= S_NOATIME | S_NOCMTIME;
 
+	mode &= S_IFMT;
 	switch (mode) {
 	case S_IFDIR:
 		inode->i_private = oe;
--- a/fs/overlayfs/overlayfs.h
+++ b/fs/overlayfs/overlayfs.h

@@ -181,6 +181,7 @@ static inline void ovl_copyattr(struct i
 {
 	to->i_uid = from->i_uid;
 	to->i_gid = from->i_gid;
+	to->i_mode = from->i_mode;
 }
 
 /* dir.c */