netdev - Re: [PATCH net v2] net: bridge: Fix ethernet header pointer before check skb forwardable

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Message-ID: <fec59e13-bf9b-9bce-c662-3e044ade6c33@lab.ntt.co.jp>
Date:   Tue, 15 Jan 2019 16:49:56 +0900
From:   Toshiaki Makita <makita.toshiaki@....ntt.co.jp>
To:     wangyunjian <wangyunjian@...wei.com>
Cc:     netdev@...r.kernel.org, xudingke@...wei.com,
        bridge@...ts.linux-foundation.org,
        Nkolay Aleksandrov <nikolay@...ulusnetworks.com>,
        Roopa Prabhu <roopa@...ulusnetworks.com>
Subject: Re: [PATCH net v2] net: bridge: Fix ethernet header pointer before
 check skb forwardable

On 2019/01/15 12:12, wangyunjian wrote:
> From: Yunjian Wang <wangyunjian@...wei.com>
> 
> The skb header should be set to ethernet header before using
> is_skb_forwardable. Because the ethernet header length has been
> considered in is_skb_forwardable(including dev->hard_header_len
> length).
> 
> To reproduce the issue:
> 1, add 2 ports on linux bridge br using following commands:
> $ brctl addbr br
> $ brctl addif br eth0
> $ brctl addif br eth1
> 2, the mtu of eth0 and eth1 is 1500
> 3, send a 1504 packet from eth0 to eth1
> 
> So the expect result is packet larger than 1500 cannot pass through
> eth0 and eth1. But currently, the packet passes through success, it
> means eth1's mtu limit donen't take effect.

I agree with the change but this test does not look appropriate.
In the first place is_skb_forwardable() accepts 4 bytes extra size (for
VLAN header). Doesn't your test case fail even after the change?

-- 
Toshiaki Makita