Re: [PATCH] ovl: xattr filter fix

[Vivek Goyal]

On Thu, Jun 02, 2016 at 10:13:33AM +0200, Miklos Szeredi wrote:
> a) ovl_need_xattr_filter() is wrong, we can have multiple lower layers
> overlaid, all of which (except the lowest one) honouring the
> "trusted.overlay.opaque" xattr.  So need to filter everything except the
> bottom and the pure-upper layer.
> 
> b) we no longer can assume that inode is attached to dentry in
> get/setxattr.
> 
> This patch unconditionally filters private xattrs to fix both of the above.
> Performance impact for get/removexattrs is likely in the noise.
> 
> For listxattrs it might be measurable in pathological cases, but I very
> much hope nobody cares.  If they do, we'll fix it then.
> 
> Reported-by: Vivek Goyal <vgoyal@xxxxxxxxxx>
> Signed-off-by: Miklos Szeredi <mszeredi@xxxxxxxxxx>
> Fixes: b96809173e94 ("security_d_instantiate(): move to the point prior to attaching dentry to inode")

Hi Miklos,

This patch fixes the issue for me. Thanks.

Reviewed-by: Vivek Goyal <vgoyal@xxxxxxxxxx>

Vivek

> ---
>  fs/overlayfs/inode.c |   26 ++++++--------------------
>  1 file changed, 6 insertions(+), 20 deletions(-)
> 
> --- a/fs/overlayfs/inode.c
> +++ b/fs/overlayfs/inode.c
> @@ -238,41 +238,27 @@ int ovl_setxattr(struct dentry *dentry,
>  	return err;
>  }
>  
> -static bool ovl_need_xattr_filter(struct dentry *dentry,
> -				  enum ovl_path_type type)
> -{
> -	if ((type & (__OVL_PATH_PURE | __OVL_PATH_UPPER)) == __OVL_PATH_UPPER)
> -		return S_ISDIR(dentry->d_inode->i_mode);
> -	else
> -		return false;
> -}
> -
>  ssize_t ovl_getxattr(struct dentry *dentry, struct inode *inode,
>  		     const char *name, void *value, size_t size)
>  {
> -	struct path realpath;
> -	enum ovl_path_type type = ovl_path_real(dentry, &realpath);
> +	struct dentry *realdentry = ovl_dentry_real(dentry);
>  
> -	if (ovl_need_xattr_filter(dentry, type) && ovl_is_private_xattr(name))
> +	if (ovl_is_private_xattr(name))
>  		return -ENODATA;
>  
> -	return vfs_getxattr(realpath.dentry, name, value, size);
> +	return vfs_getxattr(realdentry, name, value, size);
>  }
>  
>  ssize_t ovl_listxattr(struct dentry *dentry, char *list, size_t size)
>  {
> -	struct path realpath;
> -	enum ovl_path_type type = ovl_path_real(dentry, &realpath);
> +	struct dentry *realdentry = ovl_dentry_real(dentry);
>  	ssize_t res;
>  	int off;
>  
> -	res = vfs_listxattr(realpath.dentry, list, size);
> +	res = vfs_listxattr(realdentry, list, size);
>  	if (res <= 0 || size == 0)
>  		return res;
>  
> -	if (!ovl_need_xattr_filter(dentry, type))
> -		return res;
> -
>  	/* filter out private xattrs */
>  	for (off = 0; off < res;) {
>  		char *s = list + off;
> @@ -302,7 +288,7 @@ int ovl_removexattr(struct dentry *dentr
>  		goto out;
>  
>  	err = -ENODATA;
> -	if (ovl_need_xattr_filter(dentry, type) && ovl_is_private_xattr(name))
> +	if (ovl_is_private_xattr(name))
>  		goto out_drop_write;
>  
>  	if (!OVL_TYPE_UPPER(type)) {