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

Pekka Enberg
2008-07-25T10:42:20Z

On Fri, 2008-07-25 at 10:02 +0200, Dieter Ries wrote:
> Pekka Enberg schrieb:
> > On Thu, 2008-07-24 at 11:51 -0700, Andrew Morton wrote:
> >> 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?
> >
> > Apparently it didn't but it did fix Dieter's problem:
> >
> > http://lkml.org/lkml/2008/7/24/337
> >
> > Dieter, can we add a Tested-by tag from you to this patch?
> >
>
> Yes, it definitely fixed my issue and I have not encountered
> further problems with the patch. The machine
> is running fine with it.
>
> Do I have to explicitly add my
> Tested-by: Dieter Ries <clip2@gmx.de>
> tag somewhere (if yes, where?) or is this enough for you?

No, that's fine. The people who are merging the patch can pick it up.
Thanks a lot for your help!

Pekka