Re: [GIT PULL] overlayfs update for 4.18

From: Al Viro
Date: Sun Jun 10 2018 - 01:56:05 EST

On Fri, Jun 08, 2018 at 11:52:08PM -0700, Christoph Hellwig wrote:
> On Fri, Jun 08, 2018 at 02:13:30PM +0200, Miklos Szeredi wrote:
> > Hi Linus,
> >
> > Please pull from:
> >
> > git:// tags/ovl-update-4.18
> >
> > This contains two new features:
> >
> > 1) Stack file operations: this allows removal of several hacks from the
> > VFS, proper interaction of read-only open files with copy-up,
> > possibility to implement fs modifying ioctls properly, and others.
> Which includews all kinds of NAKed or at least non-acked VFS changes.

Umm... The worst of yours had been ->pre_mmap(), right? He *did* drop that...

> Please get these through Als tree after proper review first.

OK, summary of sort (see fsdevel thread for details):
* path_open() is dubious; why not simply use vfsmount/dentry from the
right layer when opening an underlying file? Then it would be vfs_open()...
* ovl_mmap() is broken, plain and simple. Failure ends up leaking
a layer struct file *and* doing double fput() on overlayfs one.
* ovl_mmap() is also trivially DoSable - you can trigger tons and tons
of reopens, each sticking a new (writable layer) struct file into a vma.
We *do* want some scheme avoiding once-per-operations reopens in the
copied-up-after-r/o-open case. See possible kinda-sorta solution on fsdevel;
I'm not sure I like it, though.

The rest is pretty minor.