Messages in this thread | | | Date | Thu, 24 Jul 2008 15:31:32 +0200 | From | Patrick McHardy <> | Subject | Re: [regression] nf_iterate(), BUG: unable to handle kernel NULL pointer dereference |
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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.
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