linux-kernel - Re: [ovs-dev] [PATCH net] openvswitch: Fix mask generation for IPv6 labels.

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Message-ID: <CALnjE+otirroKNXE7qbUHfoTifipp8LJ6g8yNsLz0dBjm3PUsQ@mail.gmail.com>
Date:	Wed, 19 Nov 2014 12:33:10 -0800
From:	Pravin Shelar <pshelar@...ira.com>
To:	Joe Stringer <joestringer@...ira.com>
Cc:	"dev@...nvswitch.org" <dev@...nvswitch.org>,
	netdev <netdev@...r.kernel.org>,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: [ovs-dev] [PATCH net] openvswitch: Fix mask generation for IPv6 labels.

On Wed, Nov 19, 2014 at 11:51 AM, Joe Stringer <joestringer@...ira.com> wrote:
> On Wednesday, November 19, 2014 11:08:35 Pravin Shelar wrote:
>> On Wed, Nov 19, 2014 at 9:48 AM, Joe Stringer <joestringer@...ira.com>
> wrote:
>> > On Wednesday, November 19, 2014 00:11:01 Pravin Shelar wrote:
>> >> On Tue, Nov 18, 2014 at 11:25 PM, Joe Stringer <joestringer@...ira.com>
>> >
>> > wrote:
>> >> > On 18 November 2014 22:09, Pravin Shelar <pshelar@...ira.com> wrote:
>> >> >> On Tue, Nov 18, 2014 at 10:54 AM, Joe Stringer
>> >> >> <joestringer@...ira.com>
>> >> >>
>> >> >> wrote:
>> >> >> > When userspace doesn't provide a mask, OVS datapath generates a
>> >> >> > fully unwildcarded mask for the flow. This is done by taking a
>> >> >> > copy of the flow key, then iterating across its attributes,
>> >> >> > setting all values to 0xff. This works for most attributes, as the
>> >> >> > length of the netlink attribute typically matches the length of
>> >> >> > the value. However, IPv6 labels only use the lower 20 bits of the
>> >> >> > field. This patch makes a special case to handle this.
>> >> >> >
>> >> >> > This fixes the following error seen when installing IPv6 flows
>> >> >> > without a mask:
>> >> >> >
>> >> >> > openvswitch: netlink: Invalid IPv6 flow label value
>> >> >> > (value=ffffffff, max=fffff)
>> >> >>
>> >> >> We should allow exact match mask here rather than generating
>> >> >> wildcarded mask. So that ovs can catch invalid ipv6.label.
>> >> >
>> >> > I don't quite follow, I thought this was exact-match? (The existing
>> >> > function sets all bits to 1)
>> >>
>> >> With 0xffffffff value we can exact match on all ipv6.lable bits.
>> >
>> > The label field is only 20 bits. The other bits in the same word of the
>> > IPv6 header are for version (fixed) and traffic class (handled
>> > separately). We don't do anything with the other bits.
>>
>> This is just to make sure that we do not use those field for any thing
>> else. Masking those extra bits can hide incorrect ipv6 key extraction.
>
> Oh, I see. I meant something more like:
>
> ipv6_key->ipv6_label &= htonl(0xFFF00000);
> ipv6_key->ipv6_label |= htonl(0x000FFFFF);
>
> (Which would propagate the invalid bits from the flow key, but actually produce
> an exact match).

yes, it can wildcard unused bits.
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