Re: Comment on nf_queue NF_STOLEN patch

[Eric Dumazet <eric.dumazet@gmail.com>]

Le mardi 18 octobre 2011 à 15:08 -0400, Jim Sansing a écrit :
> I have been working on a kernel module that registers with netfilter,
> and I noticed that a patch was added to nf_queue that changed the
> handling of return code NF_FILTER from 'do nothing' to 'free the skb'. 
> I'm not sure which kernel version this went in, but the date of the
> patch is Feb, 19, 2010.
> 
> Everything I have read about netfilter states that it is up to the
> netfilter hook to free the skb if NF_STOLEN is returned.  The
> implications of this patch from a hook programming perspective are:
> 
> 1) If the skb is used after the return from the hook, it must be cloned.
> 2) The original skb must not be freed.
> 
> I suggest that a comment be added to include/linux/netfilter.h that says
> explicitly the skb will be freed if NF_STOLEN is returned.

But its not true. Just read the code.

If you are working on this stuff I recommend you take a look at
commits :

c6675233f9015d3c0460c8aab53ed9b99d915c64
(netfilter: nf_queue: reject NF_STOLEN verdicts from userspace)

fad54440438a7c231a6ae347738423cbabc936d9
(netfilter: avoid double free in nf_reinject)

64507fdbc29c3a622180378210ecea8659b14e40
(netfilter: nf_queue: fix NF_STOLEN skb leak)

3bc38712e3a6e0596ccb6f8299043a826f983701
([NETFILTER]: nf_queue: handle NF_STOP and unknown verdicts in
nf_reinject)