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

[Oleg Nesterov]

Damn, sorry for the spam.

So I am going to send the patch from
https://lore.kernel.org/all/20240904095449.GA28781@xxxxxxxxxx/

To me it looks like a good cleanup regardless, and unless I am totally
confused it should fix the problem with use-after-free.

Oleg.

On 09/11, Oleg Nesterov wrote:
>
> 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.