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

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Date:   Mon, 14 Jan 2019 04:05:23 +0000
From:   wangyunjian <wangyunjian@...wei.com>
To:     Andrew Lunn <andrew@...n.ch>
CC:     "netdev@...r.kernel.org" <netdev@...r.kernel.org>,
        xudingke <xudingke@...wei.com>
Subject: RE: [PATCH net] bridge: Fix ethernet header pointer before check
 skb forwardable

> -----Original Message-----
> From: Andrew Lunn [mailto:andrew@...n.ch]
> Sent: Saturday, January 12, 2019 10:55 PM
> To: wangyunjian <wangyunjian@...wei.com>
> Cc: netdev@...r.kernel.org; xudingke <xudingke@...wei.com>
> Subject: Re: [PATCH net] bridge: Fix ethernet header pointer before check
> skb forwardable
> 
> On Sat, Jan 12, 2019 at 06:28:27PM +0800, wangyunjian wrote:
> > From: Yunjian Wang <wangyunjian@...wei.com>
> >
> > The skb header should be set to ethernet header before using
> > is_skb_forwardable(including dev->hard_header_len length).
> 
> Hi Yunjian
> 
> I don't see any recent changes in this code. Do you know why this is needed
> now, yet it seemed to work before? Do you have a fixes: tag for where it
> broke?
> 
> Thanks
> 	Andrew

Hi Andrew

This change is commit f6367b4660dde412f9b7af94763efb1d89cefb74(
bridge: use is_skb_forwardable in forward path).

I found it when I was testing the vNIC(virtio-net) 's mtu. 
I add 2 port on linux bridge br using following commands
brctl addbr br
brctl addif br eth0
brctl addif br eth1

The mtu of eth0 and eth1 is 1500，so the expect result is packet larger than
1500 cannot pass through eth0 and eth1.But currently, when I send a 1504
packet from eth0 to eth1, the packet passes through success, it means eth1's
mtu limit donen't take effect.

Thanks
	Yunjian