Re: [PATCH] overlayfs: Ensure upper filesystem supports d_type

[Miklos Szeredi <miklos@szeredi.hu>]

On Mon, Feb 22, 2016 at 09:28:34AM -0500, Vivek Goyal wrote:
> During mount, make sure upper fs supports d_type otherwise error out.
> 
> In some instances xfs has been created with ftype=0 and there if a file
> on lower fs is removed, overlay leaves a whiteout in upper fs but that
> whiteout does not get filtered out and is visible to overlayfs users.
> 
> And reason it does not get filtered out because upper filesystem does
> not report file type of whiteout as DT_CHR during iterate_dir().
> 
> So it seems to be a requirement that upper filesystem support d_type for
> overlayfs to work properly. Do this check during mount and fail if d_type
> is not supported.
> 
> Suggested-by: Dave Chinner <dchinner@redhat.com>
> Signed-off-by: Vivek Goyal <vgoyal@redhat.com>

Queued.  Thanks.

Miklos


> ---
>  fs/overlayfs/overlayfs.h |    1 +
>  fs/overlayfs/readdir.c   |   37 +++++++++++++++++++++++++++++++++++++
>  fs/overlayfs/super.c     |   15 +++++++++++++++
>  3 files changed, 53 insertions(+)
> 
> Index: rhvgoyal-linux/fs/overlayfs/readdir.c
> ===================================================================
> --- rhvgoyal-linux.orig/fs/overlayfs/readdir.c	2016-02-19 16:10:09.440000000 +0000
> +++ rhvgoyal-linux/fs/overlayfs/readdir.c	2016-02-22 14:09:30.745000000 +0000
> @@ -43,6 +43,7 @@ struct ovl_readdir_data {
>  	struct ovl_cache_entry *first_maybe_whiteout;
>  	int count;
>  	int err;
> +	bool d_type_supported;
>  };
>  
>  struct ovl_dir_file {
> @@ -577,3 +578,39 @@ void ovl_cleanup_whiteouts(struct dentry
>  	}
>  	inode_unlock(upper->d_inode);
>  }
> +
> +static int ovl_check_d_type(struct dir_context *ctx, const char *name,
> +			  int namelen, loff_t offset, u64 ino,
> +			  unsigned int d_type)
> +{
> +	struct ovl_readdir_data *rdd =
> +		container_of(ctx, struct ovl_readdir_data, ctx);
> +
> +	/* Even if d_type is not supported, DT_DIR is returned for . and .. */
> +	if (!strncmp(name, ".", namelen) || !strncmp(name, "..", namelen))
> +		return 0;
> +
> +	if (d_type != DT_UNKNOWN)
> +		rdd->d_type_supported = true;
> +
> +	return 0;
> +}
> +
> +/*
> + * Returns 1 if d_type is supported, 0 not supported/unknown. Negative values
> + * if error is encountered.
> + */
> +int ovl_check_d_type_supported(struct path *realpath)
> +{
> +	int err;
> +	struct ovl_readdir_data rdd = {
> +		.ctx.actor = ovl_check_d_type,
> +		.d_type_supported = false,
> +	};
> +
> +	err = ovl_dir_read(realpath, &rdd);
> +	if (err)
> +		return err;
> +
> +	return rdd.d_type_supported;
> +}
> Index: rhvgoyal-linux/fs/overlayfs/overlayfs.h
> ===================================================================
> --- rhvgoyal-linux.orig/fs/overlayfs/overlayfs.h	2016-02-19 16:10:09.440000000 +0000
> +++ rhvgoyal-linux/fs/overlayfs/overlayfs.h	2016-02-22 14:09:30.746000000 +0000
> @@ -166,6 +166,7 @@ extern const struct file_operations ovl_
>  int ovl_check_empty_dir(struct dentry *dentry, struct list_head *list);
>  void ovl_cleanup_whiteouts(struct dentry *upper, struct list_head *list);
>  void ovl_cache_free(struct list_head *list);
> +int ovl_check_d_type_supported(struct path *realpath);
>  
>  /* inode.c */
>  int ovl_setattr(struct dentry *dentry, struct iattr *attr);
> Index: rhvgoyal-linux/fs/overlayfs/super.c
> ===================================================================
> --- rhvgoyal-linux.orig/fs/overlayfs/super.c	2016-02-19 16:10:09.440000000 +0000
> +++ rhvgoyal-linux/fs/overlayfs/super.c	2016-02-22 14:09:30.746000000 +0000
> @@ -1025,6 +1025,21 @@ static int ovl_fill_super(struct super_b
>  			sb->s_flags |= MS_RDONLY;
>  			ufs->workdir = NULL;
>  		}
> +
> +		/*
> +		 * Upper should support d_type, else whiteouts are visible.
> +		 * Given workdir and upper are on same fs, we can do
> +		 * iterate_dir() on workdir.
> +		 */
> +		err = ovl_check_d_type_supported(&workpath);
> +		if (err < 0)
> +			goto out_put_workdir;
> +
> +		if (!err) {
> +			pr_err("overlayfs: upper fs needs to support d_type.\n");
> +			err = -EINVAL;
> +			goto out_put_workdir;
> +		}
>  	}
>  
>  	err = -ENOMEM;