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SubjectRe: [Bridge] [BUG] Dropping fragmented IP packets within VLAN frames on bridge
On Saturday 26 May 2007, Patrick McHardy wrote:
> Adam Osuchowski wrote:
> > 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.

And could we separe the conditions for that into a static helper function
explaining each of these conditions? e.g. sth. like that:

static bool br_nf_need_fragment(struct sk_buff *skb)
/* Plain IP packet does not fit in MTU */
if (!(skb->protocol == htons(ETH_P_IP) && skb->len > skb->dev->mtu))
return true;

/* VLAN encapsulated IP packet does not fit in MTU */
if (IS_VLAN_IP(skb) && skb->len > skb->dev->mtu - VLAN_HLEN)
return true;

/* PPPoE encapsulated IP packet does not fit in MTU */
if (IS_PPPOE_IP(skb) && skb->len > skb->dev->mtu - PPPOE_SES_HLEN)
return true;

return false;

and then br_nf_dev_queue_xmit() becomes:

static int br_nf_dev_queue_xmit(struct sk_buff *skb)
if (br_nf_need_fragment(skb) && !skb_is_gso(skb))
return ip_fragment(skb, br_dev_queue_push_xmit);
return br_dev_queue_push_xmit(skb);

which is much more readable, more documented and doesn't contain a condition monster :-)

@Patrick: Could you check, wether the PPPoE case is correct?

What do you think? Should I submit a patch for that?

Best Regards

Ingo Oeser
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