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Date:   Sun, 17 May 2020 14:34:40 -0700
From:   Florian Fainelli <f.fainelli@...il.com>
To:     Vladimir Oltean <olteanv@...il.com>, andrew@...n.ch,
        vivien.didelot@...il.com
Cc:     davem@...emloft.net, kuba@...nel.org, eric.dumazet@...il.com,
        jiri@...lanox.com, idosch@...sch.org, rmk+kernel@...linux.org.uk,
        netdev@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH net-next] net: dsa: sja1105: disable rxvlan offload for
 the DSA master



On 5/12/2020 4:49 PM, Vladimir Oltean wrote:
> From: Vladimir Oltean <vladimir.oltean@....com>
> 
> On sja1105 operating in best_effort_vlan_filtering mode (when the TPID
> of the DSA tags is 0x8100), it can be seen that __netif_receive_skb_core
> calls __vlan_hwaccel_clear_tag right before passing the skb to the DSA
> packet_type handler.
> 
> This means that the tagger does not see the VLAN tag in the skb, nor in
> the skb meta data.
> 
> The patch that started zeroing the skb VLAN tag is:
> 
>    commit d4b812dea4a236f729526facf97df1a9d18e191c
>    Author: Eric Dumazet <edumazet@...xxxxxxx>
>    Date:   Thu Jul 18 07:19:26 2013 -0700
> 
>        vlan: mask vlan prio bits
> 
>        In commit 48cc32d38a52d0b68f91a171a8d00531edc6a46e
>        ("vlan: don't deliver frames for unknown vlans to protocols")
>        Florian made sure we set pkt_type to PACKET_OTHERHOST
>        if the vlan id is set and we could find a vlan device for this
>        particular id.
> 
>        But we also have a problem if prio bits are set.
> 
>        Steinar reported an issue on a router receiving IPv6 frames with a
>        vlan tag of 4000 (id 0, prio 2), and tunneled into a sit device,
>        because skb->vlan_tci is set.
> 
>        Forwarded frame is completely corrupted : We can see (8100:4000)
>        being inserted in the middle of IPv6 source address :
> 
>        16:48:00.780413 IP6 2001:16d8:8100:4000:ee1c:0:9d9:bc87 >
>        9f94:4d95:2001:67c:29f4::: ICMP6, unknown icmp6 type (0), length 64
>               0x0000:  0000 0029 8000 c7c3 7103 0001 a0ae e651
>               0x0010:  0000 0000 ccce 0b00 0000 0000 1011 1213
>               0x0020:  1415 1617 1819 1a1b 1c1d 1e1f 2021 2223
>               0x0030:  2425 2627 2829 2a2b 2c2d 2e2f 3031 3233
> 
>        It seems we are not really ready to properly cope with this right now.
> 
>        We can probably do better in future kernels :
>        vlan_get_ingress_priority() should be a netdev property instead of
>        a per vlan_dev one.
> 
>        For stable kernels, lets clear vlan_tci to fix the bugs.
> 
>        Reported-by: Steinar H. Gunderson <sesse@...xxxxxxx>
>        Signed-off-by: Eric Dumazet <edumazet@...xxxxxxx>
>        Signed-off-by: David S. Miller <davem@...xxxxxxxxxx>
> 
> The patch doesn't say why "we are not really ready to properly cope with
> this right now", and hence why the best solution is to remove the VLAN
> tag from skb's that don't have a local VLAN sub-interface interested in
> them. And I have no idea either.
> 
> But the above patch has a loophole: if the VLAN tag is not
> hw-accelerated, it isn't removed from the skb if there is no VLAN
> sub-interface interested in it (our case). So we are hooking into the
> .ndo_fix_features callback of the DSA master and clearing the rxvlan
> offload feature, so the DSA tagger will always see the VLAN as part of
> the skb data. This is symmetrical with the ETH_P_DSA_8021Q case and does
> not need special treatment in the tagger.
> 
> If there was an API by which the dsa tag_8021q module would declare its
> interest in servicing VLANs 1024-3071, such that the packets wouldn't be
> classified as PACKET_OTHERHOST, and if that API wasn't as tightly
> integrated with the 8021q module as vlan_find_dev/vlan_group_set_device
> are, I would be interested in using it, but so far I couldn't find it.
> With this patch, even though the frames still are PACKET_OTHERHOST, at
> least the VLAN tag reaches far enough that the DSA packet_type handler
> sees and consumes it.

The approach seems fine to me, I have to admit I am equally confused 
about Eric's patch other than it being a stop gap measure for a problem 
that was observed.

Reviewed-by: Florian Fainelli <f.fainelli@...il.com>

In case we have a DSA master that does support NETIF_F_HW_VLAN_CTAG_RX 
though we should probably ensure that we install a VLAN filter there 
too, which we do not do currently.
-- 
Florian

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