netdev - Re: [PATCH] vlan: mask vlan prio bits

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Date:	Thu, 18 Jul 2013 08:49:30 -0700
From:	Eric Dumazet <eric.dumazet@...il.com>
To:	David Miller <davem@...emloft.net>
Cc:	"Steinar H. Gunderson" <sesse@...gle.com>,
	Florian Zumbiehl <florz@...rz.de>,
	netdev <netdev@...r.kernel.org>,
	Patrick McHardy <kaber@...sh.net>
Subject: Re: [PATCH] vlan: mask vlan prio bits

On Thu, 2013-07-18 at 07:19 -0700, Eric Dumazet wrote:
> From: Eric Dumazet <edumazet@...gle.com>
> 
> 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@...gle.com>
> Signed-off-by: Eric Dumazet <edumazet@...gle.com>
> ---

While looking at the 'future' patches for net-next, I found
that vlan_dev_get_egress_qos_mask() uses no protection at all
while doing the lookup in hash table.

This is racy with concurrent insert/deletes, eventually.

This probably needs a bit of RCU care ;)


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