On Mon, Jun 13, 2022 at 05:44:35PM +0100, Matthew Wilcox wrote:
> On Mon, Jun 13, 2022 at 09:23:15AM -0700, Kees Cook wrote:
> > On Sun, Jun 12, 2022 at 10:32:25PM +0100, Matthew Wilcox (Oracle) wrote:
> > > vmalloc does not allocate a vm_struct for vm_map_ram() areas. That causes
> > > us to deny usercopies from those areas. This affects XFS which uses
> > > vm_map_ram() for its directories.
> > >
> > > Fix this by calling find_vmap_area() instead of find_vm_area().
> >
> > Thanks for the fixes!
> >
> > > [...]
> > > + /* XXX: We should also abort for free vmap_areas */
> >
> > What's needed to detect this?
>
> I'm not entirely sure. I only just learned of the existence of this
> struct ;-)
>
> /*
> * The following two variables can be packed, because
> * a vmap_area object can be either:
> * 1) in "free" tree (root is free_vmap_area_root)
> * 2) or "busy" tree (root is vmap_area_root)
> */
> union {
> unsigned long subtree_max_size; /* in "free" tree */
> struct vm_struct *vm; /* in "busy" tree */
> };
>
> Hmm. Actually, we only search vmap_area_root, so I suppose it can't
> be a free area. So this XXX can be removed, as we'll get NULL back
> if we've got a pointer to a free area. Ulad, do I have this right?
>
Yep, we find here only allocated areas which bind to the "vmap_area_root"
tree, so it can not be a freed area. So we will not get a pointer to the
free area :)
--
Uladzislau Rezki
