Re: [PATCH] uprobes: use vm_special_mapping close() functionality

[Oleg Nesterov <oleg@redhat.com>]

I guess VM_SEALED could help, but it depends on CONFIG_64BIT


On 09/11, Oleg Nesterov wrote:
>
> On 09/03, Sven Schnelle wrote:
> >
> > +static void uprobe_clear_state(const struct vm_special_mapping *sm, struct vm_area_struct *vma)
> > +{
> > +	struct xol_area *area = container_of(vma->vm_private_data, struct xol_area, xol_mapping);
> > +
> > +	mutex_lock(&delayed_uprobe_lock);
> > +	delayed_uprobe_remove(NULL, vma->vm_mm);
> > +	mutex_unlock(&delayed_uprobe_lock);
> > +
> > +	if (!area)
> > +		return;
> > +
> > +	put_page(area->pages[0]);
> > +	kfree(area->bitmap);
> > +	kfree(area);
> > +}
> > +
> >  static struct xol_area *__create_xol_area(unsigned long vaddr)
> >  {
> >  	struct mm_struct *mm = current->mm;
> > @@ -1481,6 +1500,7 @@ static struct xol_area *__create_xol_area(unsigned long vaddr)
> >
> >  	area->xol_mapping.name = "[uprobes]";
> >  	area->xol_mapping.fault = NULL;
> > +	area->xol_mapping.close = uprobe_clear_state;
> 
> Ah, no, we can't do this :/
> 
> A malicious application can munmap() its "[uprobes]" vma and free
> area/pages/bitmap. If this application hits the uprobe breakpoint after
> that it will use the freed memory.
> 
> And no, "mm->uprobes_state.xol_area = NULL" in uprobe_clear_state() won't
> help. Say, another thread can sleep on area.wq when munmap() is called.
> 
> Sorry, I should have realized that immediately, but I didn't :/
> 
> Andrew, this is uprobes-use-vm_special_mapping-close-functionality.patch
> in mm-stable
> 
> Oleg.