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

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Message-ID: <34EFBCA9F01B0748BEB6B629CE643AE60C9DC941@DGGEMM533-MBX.china.huawei.com>
Date:   Wed, 16 Jan 2019 12:44:16 +0000
From:   wangyunjian <wangyunjian@...wei.com>
To:     Toshiaki Makita <makita.toshiaki@....ntt.co.jp>
CC:     "netdev@...r.kernel.org" <netdev@...r.kernel.org>,
        xudingke <xudingke@...wei.com>,
        "bridge@...ts.linux-foundation.org" 
        <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

> -----Original Message-----
> From: Toshiaki Makita [mailto:makita.toshiaki@....ntt.co.jp]
> Sent: Tuesday, January 15, 2019 3:50 PM
> To: wangyunjian <wangyunjian@...wei.com>
> Cc: netdev@...r.kernel.org; xudingke <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

Before executing the functions is_skb_forwardable() and skb_push(), the actual
packet consist of the follwing parts, Data 1480, UDP 8, IP 20, Ethernet 14, VLAN 4.
And the value of variables are dev->mtu=1500, dev->hard_header_len=14 and
skb->len=1508. The packet cannot pass through.

I will fix the previous description of packet len.

Thanks,
	Yunjian