Hi,
On Wed, 28 Sep 2016 12:30:56 +0200, dan...@iogearbox.net wrote:
> > @@ -4608,6 +4608,8 @@ int skb_vlan_push(struct sk_buff *skb, __be16
> > vlan_proto, u16 vlan_tci)
> >
> > skb->protocol = skb->vlan_proto;
> > skb->mac_len += VLAN_HLEN;
> > + if (offset)
> > + offset += VLAN_HLEN;
> >
> > skb_postpush_rcsum(skb, skb->data + (2 * ETH_ALEN), VLAN_HLEN);
> > __skb_pull(skb, offset);
>
> This looks much better indeed than your v1 of this patch.
Yep, after some meditation and history digging I happened to notice I
was barking at the wrong tree.
> So the issue might only be visible to act_vlan as the other remaining user of
> skb_vlan_push().
Yes, this is correct. I'll amend the log message to express that.
The bug occurs for callers of skb_vlan_push() whose data is not
pointing at mac_header.
> My only question would be:
> what about __skb_vlan_pop(), wouldn't that then need the same adjustment
> a la offset -= VLAN_HLEN?
Well, theoretically, yes; but caller may expect 2 different things:
(assuming tags are in-payload)
(1) suppose upon entry we have
DA,SA,0x8100,TCI,0x0800,
^ ^
mac_hdr data
initial offset is 18, and after current unwinding code we'll get
DA,SA,0x0800,4_bytes,
^ ^
mac_hdr data
which is probably incorrect, adjustment 'offset -= VLAN_HLEN' is needed.
(2) suppose upon entry we have
DA,SA,0x8100,TCI,0x0800
^ ^
mac_hdr data
initial offset is 14, and after current unwinding code we'll get
DA,SA,0x0800,
^ ^
mac_hdr data
which is probably what user has intended.
(had we adjusted offset to be 10, 'data' would point into SA)
From test I've made using act_vlan upon ingress on QinQ tags, existing call
provides data as in (2).
Thoughts?
Should we adjust "offset" back, only if resulting offset is >=14 ?
Thanks,
Shmulik
