ovl: Copy up underlying inode's ->i_mode to overlay inode

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 <eguan@redhat.com>
Signed-off-by: Miklos Szeredi <mszeredi@redhat.com>
Fixes: 4bacc9c9234c ("overlayfs: Make f_path always point to the overlay and f_inode to the underlay")
Cc: <stable@vger.kernel.org>

2 files changed, 2 insertions, 2 deletions

diff --git a/fs/overlayfs/inode.c b/fs/overlayfs/inode.c
index 1233992a7c47..d1cdc60dd68f 100644
--- a/fs/overlayfs/inode.c
+++ b/fs/overlayfs/inode.c
@@ -413,12 +413,11 @@ struct inode *ovl_new_inode(struct super_block *sb, umode_t mode,
         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;
diff --git a/fs/overlayfs/overlayfs.h b/fs/overlayfs/overlayfs.h
index 4bd9b5ba8f42..cfbca53590d0 100644
--- a/fs/overlayfs/overlayfs.h
+++ b/fs/overlayfs/overlayfs.h
@@ -187,6 +187,7 @@ static inline void ovl_copyattr(struct inode *from, struct inode *to)
 {
         to->i_uid = from->i_uid;
         to->i_gid = from->i_gid;
+        to->i_mode = from->i_mode;
 }
 
 /* dir.c */