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

Pekka Enberg
2008-07-24T13:34:51Z

On Thu, 2008-07-24 at 15:31 +0200, Patrick McHardy wrote:
> Pekka Enberg wrote:
> > On Thu, 2008-07-24 at 14:49 +0200, Patrick McHardy wrote:
> >> Pekka Enberg wrote:
> >>> Hmm, why do you think it's related? It looks like elem->hook() is a
> >>> NULL pointer but my patch shouldn't make any difference here...
> >> No, its already in ipv4_confirm, so its most likely helper->help()
> >> thats NULL, which is contained in an extension.
> >>
> >> The reason why I think its this patch is (quoting from an old
> >> email that I never got a response to):
> >
> > Oh, I'm really sorry about that.
>
> No problem :)
>
> >> ---
> >> 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?