Date: Tue, 12 Jan 2010 09:26:29 +0200 From: Alexander Motin <mav@FreeBSD.org> To: Maxim Ignatenko <gelraen.ua@gmail.com> Cc: freebsd-net@freebsd.org Subject: Re: ng_patch node Message-ID: <4B4C2425.2010402@FreeBSD.org> In-Reply-To: <1263262983.00205781.1263251401@10.7.7.3> References: <1263262983.00205781.1263251401@10.7.7.3>
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Maxim Ignatenko wrote:
> I've written netgraph node able to modify arbitrary (8|16|32)-bit
> unsigned integer in passing packets. Node applies one of =,+,-,&,| and
> ^ operations to number at given offset.
> Modification applied to each packet received on "in" hook. If "out"
> hook is connected - resulting packets passed on it, otherwise -
> returned back on "in" (for more easy use with ng_ipfw). Packets
> received on "out" hook passed on "in" unmodified.
> Node supports two control messages: "getconfig" and "setconfig".
> Configuration represented in next structure:
> struct ng_patch_config {
> uint32_t value; /* argument passed to requested operation */
> uint32_t offset; /* offset in bytes */
> uint32_t length; /* 1,2 or 4 bytes */
> uint32_t mode; /* operation code: 1 - "=", 2 - "+", 3 -
> "-", 4 - "&", 5 - "|", 6 - "^" */
> };
> Same names used in ASCII representation.
>
> I wanted to make ipfw able to modify TTL and ToS fields in IP packets,
> but after some generalization idea looked like described above.
>
> Next patch made against 8-STABLE r200201
Just few stones into your garden:
> + if (((struct ng_patch_config *)msg->data)->offset < 0)
> + error = EINVAL;
As I see, offset field is unsigned there.
> + case 4:
> + *((uint32_t *)dst) +=
> priv->value4;
I think such dereference may crash archs with strong alignment
requirements. m_copydata/m_copyback could do it possibly slower, but
safer and wouldn't require m_pullup.
Also result of such multi-byte operations is endian-dependent. I would
be nice to do hton/ntoh somewhere.
Also, what's about checksums?
--
Alexander Motin
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