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

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Date:   Mon, 14 Jan 2019 14:51:34 +0100
From:   Andrew Lunn <andrew@...n.ch>
To:     wangyunjian <wangyunjian@...wei.com>
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

On Mon, Jan 14, 2019 at 04:05:23AM +0000, wangyunjian wrote:
> > -----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.

Hi Yunjian

Thanks for the explanation. Please could you improve the description
in the patch. Also, add a Fixes tag:

Fixes: f6367b4660dd ("bridge: use is_skb_forwardable in forward path")

Thanks
	Andrew