Re: [syzbot] [io-uring?] KASAN: null-ptr-deref Write in sys_io_uring_register

[Tamir Duberstein <tamird@gmail.com>]

On Wed, Dec 4, 2024 at 11:25 AM Matthew Wilcox <willy@infradead.org> wrote:
>
> On Wed, Dec 04, 2024 at 09:17:27AM -0700, Jens Axboe wrote:
> > >   XA_STATE(xas, xa, index);
> > > - return xas_result(&xas, xas_store(&xas, NULL));
> > > + return xas_result(&xas, xa_zero_to_null(xas_store(&xas, NULL)));
> > >  }
> > >  EXPORT_SYMBOL(__xa_erase);
> > >
> > > This would explain deletion of a reserved entry returning
> > > `XA_ZERO_ENTRY` rather than `NULL`.
> >
> > Yep this works.
> >
> > > My apologies for this breakage. Should I send a new version? A new
> > > "fixes" patch?
> >
> > Since it seems quite drastically broken, and since it looks like Andrew
> > is holding it, seems like the best course of action would be to have it
> > folded with the existing patch.
>
> ... and please include an addition to the test-suite that would catch
> this bug.
>
> Wait, why doesn't this one catch it?  You did run the test-suite, right?
>
>         /* xa_insert treats it as busy */
>         XA_BUG_ON(xa, xa_reserve(xa, 12345678, GFP_KERNEL) != 0);
>         XA_BUG_ON(xa, xa_insert(xa, 12345678, xa_mk_value(12345678), 0) !=
>                         -EBUSY);
>         XA_BUG_ON(xa, xa_empty(xa));
>         XA_BUG_ON(xa, xa_erase(xa, 12345678) != NULL);
>         XA_BUG_ON(xa, !xa_empty(xa));

I thought I did, but when I ran it again just now, this test did catch
it. So there is coverage.