linux-kernel - Re: [Bridge] [BUG] Dropping fragmented IP packets within VLAN frames on bridge

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Date:	Sat, 26 May 2007 10:13:24 +0200
From:	Patrick McHardy <kaber@...sh.net>
To:	Adam Osuchowski <adwol@...k.pl>
CC:	Stephen Hemminger <shemminger@...ux-foundation.org>,
	bridge@...ts.linux-foundation.org, linux-kernel@...r.kernel.org
Subject: Re: [Bridge] [BUG] Dropping fragmented IP packets within VLAN frames
 on bridge

Adam Osuchowski wrote:
> Stephen Hemminger wrote:
> 
>>It would be better to account for the tag in the length check.
>>Something like
>>	if (skb->protocol == htons(ETH_P_IP) &&
>>	    skb->len > skb->dev->mtu - (IS_VLAN_IP(skb) ? VLAN_HLEN : 0) &&
>>	    !skb_is_gso(skb))
>>		return ip_fragment ...
> 
> 
> It isn't good solution because one of IS_VLAN_IP() necessary condition is
> 
>     skb->protocol == htons(ETH_P_8021Q)
> 
> which is, of course, mutually exclusive with
> 
>     skb->protocol == htons(ETH_P_IP)
> 
> from br_nf_dev_queue_xmit(). IMHO, one should check length of ETH_P_IP
> and ETH_P_8021Q frames separately:
> 
>     if (((skb->protocol == htons(ETH_P_IP) && skb->len > skb->dev->mtu) ||
>         (IS_VLAN_IP(skb) && skb->len > skb->dev->mtu - VLAN_HLEN)) &&
> 	!skb_is_gso(skb))
> 	    return ip_fragment ...


net/8021q ignores the VLAN header overhead, so we should probably do the
same here for consistency. Using IS_VLAN_IP (and IS_PPPOE_IP for current
-rc) looks fine, additionally we should probably also check for
skb->nfct != NULL to make sure that at least without connection tracking
the bridge doesn't perform fragmentation.

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