netdev - Re: [PATCH net-next] net: filter: rename 'struct sk_filter' to 'struct bpf

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Message-Id: <20140728.171213.1219772609929469928.davem@davemloft.net>
Date:	Mon, 28 Jul 2014 17:12:13 -0700 (PDT)
From:	David Miller <davem@...emloft.net>
To:	pablo@...filter.org
Cc:	ast@...mgrid.com, dborkman@...hat.com, netdev@...r.kernel.org,
	linux-kernel@...r.kernel.org, willemb@...gle.com,
	netfilter-devel@...r.kernel.org
Subject: Re: [PATCH net-next] net: filter: rename 'struct sk_filter' to
 'struct bpf_prog'

From: Pablo Neira Ayuso <pablo@...filter.org>
Date: Mon, 28 Jul 2014 23:45:52 +0200

> By renaming this, you're not fixing up things the semantics. It seems
> to me you just want to find a quick path to solve inconsistencies in
> your code.

Agreed, this looks just like messing around with naming to me.

But to the original issue, that of xt_bpf, I wonder about a few things:

1) If we have a kernel pointer embedded in a user provided datastructure,
   what takes care of 32-bit compat applications uploading xt_bpf rules
   on a 64-bit kernel?  Won't the size be wrong or does it not matter
   and is in some way helped by that 8-byte alignment thing there?

2) The user can't care about the type of "filter" in xt_bpf_info, so
   we can use whatever name we want for the type.

   Therefore you can just do something like:

struct bpf_prog;

struct xt_bpf_info {
	__u16 bpf_program_num_elem;
	struct sock_filter bpf_program[XT_BPF_MAX_NUM_INSTR];

	/* only used in the kernel */
	struct bpf_prog *filter __attribute__((aligned(8)));
};

   and then you won't need any casting.
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