btrfs: copy dir permission and time when creating a stub subvolume

btrfs supports creating nested subvolumes however snapshots are not
recursive.  When a snapshot is taken of a volume which contains a
subvolume the subvolume is replaced with a stub subvolume which has the
same name and uses inode number 2[1]. The stub subvolume kept the
directory name but did not set the time or permissions of the stub
subvolume. This resulted in all time information being the current time
and ownership defaulting to root. When subvolumes and snapshots are
created using unshare this results in a snapshot directory the user
created but has no permissions for.

Test case:

  [vmuser@archvm ~]# sudo -i
  [root@archvm ~]# mkdir -p /mnt/btrfs/test
  [root@archvm ~]# chown vmuser:users /mnt/btrfs/test/
  [root@archvm ~]# exit
  logout
  [vmuser@archvm ~]$ cd /mnt/btrfs/test
  [vmuser@archvm test]$ unshare --user --keep-caps --map-auto --map-root-user
  [root@archvm test]# btrfs subvolume create subvolume
  Create subvolume './subvolume'
  [root@archvm test]# btrfs subvolume create subvolume/subsubvolume
  Create subvolume 'subvolume/subsubvolume'
  [root@archvm test]# btrfs subvolume snapshot subvolume snapshot
  Create a snapshot of 'subvolume' in './snapshot'
  [root@archvm test]# exit
  logout
  [vmuser@archvm test]$ tree -ug
  [vmuser   users   ]  .
  ├── [vmuser   users   ]  snapshot
  │   └── [vmuser   users   ]  subsubvolume  <-- Without patch perm is root:root
  └── [vmuser   users   ]  subvolume
      └── [vmuser   users   ]  subsubvolume

  5 directories, 0 files

[1] https://btrfs.readthedocs.io/en/latest/btrfs-subvolume.html#nested-subvolumes

Signed-off-by: Lee Trager <[email protected]>
Signed-off-by: David Sterba <[email protected]>

Author: ltrager

fs/btrfs/inode.c

@@ -5585,11 +5585,11 @@ struct inode *btrfs_iget(struct super_block *s, u64 ino, struct btrfs_root *root
 	return btrfs_iget_path(s, ino, root, NULL);
 }
 
-static struct inode *new_simple_dir(struct super_block *s,
+static struct inode *new_simple_dir(struct inode *dir,
 				    struct btrfs_key *key,
 				    struct btrfs_root *root)
 {
-	struct inode *inode = new_inode(s);
+	struct inode *inode = new_inode(dir->i_sb);
 
 	if (!inode)
 		return ERR_PTR(-ENOMEM);
@@ -5608,9 +5608,11 @@ static struct inode *new_simple_dir(struct super_block *s,
 	inode->i_fop = &simple_dir_operations;
 	inode->i_mode = S_IFDIR | S_IRUGO | S_IWUSR | S_IXUGO;
 	inode->i_mtime = current_time(inode);
-	inode->i_atime = inode->i_mtime;
-	inode->i_ctime = inode->i_mtime;
+	inode->i_atime = dir->i_atime;
+	inode->i_ctime = dir->i_ctime;
 	BTRFS_I(inode)->i_otime = inode->i_mtime;
+	inode->i_uid = dir->i_uid;
+	inode->i_gid = dir->i_gid;
 
 	return inode;
 }
@@ -5669,7 +5671,7 @@ struct inode *btrfs_lookup_dentry(struct inode *dir, struct dentry *dentry)
 		if (ret != -ENOENT)
 			inode = ERR_PTR(ret);
 		else
-			inode = new_simple_dir(dir->i_sb, &location, root);
+			inode = new_simple_dir(dir, &location, root);
 	} else {
 		inode = btrfs_iget(dir->i_sb, location.objectid, sub_root);
 		btrfs_put_root(sub_root);