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

On Thu, 2008-07-24 at 15:31 +0200, Patrick McHardy wrote:

Pekka Enberg wrote:

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On Thu, 2008-07-24 at 14:49 +0200, Patrick McHardy wrote:

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Pekka Enberg wrote:

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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 :)

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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 <redacted>
Signed-off-by: Pekka Enberg <redacted>

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?