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Date:	Fri, 25 Jul 2014 09:53:48 -0400
From:	Willem de Bruijn <willemb@...gle.com>
To:	Pablo Neira Ayuso <pablo@...filter.org>
Cc:	Daniel Borkmann <dborkman@...hat.com>,
	Alexei Starovoitov <ast@...mgrid.com>,
	"David S. Miller" <davem@...emloft.net>, netdev@...r.kernel.org,
	linux-kernel <linux-kernel@...r.kernel.org>,
	netfilter-devel <netfilter-devel@...r.kernel.org>
Subject: Re: [PATCH net-next] net: filter: rename 'struct sk_filter' to
 'struct bpf_prog'

>> >alternative fix for xt_bpf.h could be to replace:
>> >         /* only used in the kernel */
>> >     struct sk_filter *filter __attribute__((aligned(8)));
>> >with
>> >         /* only used in the kernel */
>> >     void *filter __attribute__((aligned(8)));
>> >
>> >but this 'void *' approach may further break broken userspace,
>> >whereas the fix implemented here is more seamless.
>>
>> Yep, that's not good, 'struct sk_filter' should never have been in a uapi
>> file actually.

This follows a convention in include/uapi/linux/netfilter/*.h that
likely predates the introduction of uapi. A search for "Used
internally by the kernel" shows many more examples. I should not have
included filter.h, however. The common behavior when using pointers
to kernel-internal structures is to have a forward declaration. I suggest
making that change, instead of changing to void *. This avoids having
to add casts where xt_bpf_info is used in net/netfilter/xt_bpf.c:

-#include <linux/filter.h>
 #include <linux/types.h>

 #define XT_BPF_MAX_NUM_INSTR   64

+struct sk_filter;
+
 struct xt_bpf_info {

I can send this as a separate patch to net-next, if that helps.

> You can just send me a patch to change it to void. It's an internal
> kernel pointer as the comment states. There is **no** way that
> userspace can lurk with that from iptables at all.
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