Re: [regression] nf_iterate(), BUG: unable to handle kernel NULL pointer dereference

Andrew Morton
2008-07-24T18:54:19Z

On Thu, 24 Jul 2008 16:34:36 +0300 Pekka Enberg <penberg@cs.helsinki.fi> wrote:

> > >> Your patch introduced a use-after-free and double-free.
> > >> krealloc() frees the old pointer, but it is still used
> > >> for the ->move operations, then freed again.
> > >>
> > >> To fix this I think we need a __krealloc() that doesn't
> > >> free the old memory, especially since it must not be
> > >> freed immediately because it may still be used in a RCU
> > >> read side (see the last part in the patch attached to
> > >> this mail (based on a kernel without your patch)).
> > >
> > > Agreed. Something like this, perhaps?
> > >
> > > [PATCH] netfilter: fix double-free and use-after free
> > >
> > > As suggested by Patrick McHardy, introduce a __krealloc() that doesn't
> > > free the original buffer to fix a double-free and use-after-free bug
> > > introduced by me in netfilter that uses RCU.
> > >
> > > Reported-by: Patrick McHardy <kaber@trash.net>
> > > Signed-off-by: Pekka Enberg <penberg@cs.helsinki.fi>
> >
> > Looks good to me, thanks.
>
> Ingo, can you please test this? Andrew, I'm at OLS so can you pick up
> the patch in your tree?

Sure. Or Patrick can do so and it can be merged via the net tree.

Ingo, did this patch actually fix something over there?