Re: [PATCH 01/11] fs: add O_BENEATH_ONLY flag to openat(2)

On Mon, Jun 30, 2014 at 01:40:40PM -0700, Andi Kleen wrote:

David Drysdale [off-list ref] writes:

quoted

Add a new O_BENEATH_ONLY flag for openat(2) which restricts the
provided path, rejecting (with -EACCES) paths that are not beneath
the provided dfd.  In particular, reject:
 - paths that contain .. components
 - paths that begin with /
 - symlinks that have paths as above.

How about bind mounts?

-Andi

-- 
ak-VuQAYsv1563Yd54FQh9/CA@public.gmane.org -- Speaking for myself only

Bind mounts won't get rejected because they just look like normal
path components.  In other words, if dir/subdir is a bind mount to
/root/dir then:
  fd = openat(AT_FDCWD, "dir/subdir", O_RDONLY|O_BENEATH_ONLY);
will work fine.