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

[David Drysdale]

On Mon, Jun 30, 2014 at 01:40:40PM -0700, Andi Kleen wrote:
> David Drysdale <drysdale@xxxxxxxxxx> writes:
> 
> > 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@xxxxxxxxxxxxxxx -- 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.
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