Re: new ...at() flag: AT_NO_JUMPS

[Matthew Wilcox]

On Sun, Apr 30, 2017 at 12:25:04AM +0100, Al Viro wrote:
> On Sat, Apr 29, 2017 at 04:17:18PM -0700, Andy Lutomirski wrote:
> > On Sat, Apr 29, 2017 at 3:04 PM, Al Viro <viro@xxxxxxxxxxxxxxxxxx> wrote:
> > > New AT_... flag - AT_NO_JUMPS
> > >
> > > Semantics: pathname resolution must not involve
> > >         * traversals of absolute symlinks
> > >         * traversals of procfs-style symlinks
> > >         * traversals of mountpoints (including bindings, referrals, etc.)
> > >         * traversal of .. in the starting point of pathname resolution.
> > 
> > Can you clarify this last one?  I assume that ".." will be rejected,
> > but what about "a/../.."?  How about "b" if b is a symlink to ".."?
> > How about "a/b" if a is a directory and b is a symlink to "../.."?
> 
> All of those will be rejected - in each of those cases pathname traversal
> leads back into the starting point with .. being the next component to
> handle.

It sounds more like AT_NO_ESCAPE ... or AT_BELOW, or something.  Perhaps
some example usages in the changelog?