Re: VLAN packets silently dropped in promiscuous mode

[Eric Dumazet <eric.dumazet@gmail.com>]

Le jeudi 30 septembre 2010 à 10:07 +0200, Roger Luethi a écrit :
> On Wed, 29 Sep 2010 10:44:26 -0700, Jesse Gross wrote:
> > On Wed, Sep 29, 2010 at 4:37 AM, Roger Luethi <rl@hellgate.ch> wrote:
> > > I noticed packets for unknown VLANs getting silently dropped even in
> > > promiscuous mode (this is true only for the hardware accelerated path).
> > > netif_nit_deliver was introduced specifically to prevent that, but the
> > > function gets called only _after_ packets from unknown VLANs have been
> > > dropped.
> > 
> > Some drivers are fixing this on a case by case basis by disabling
> > hardware accelerated VLAN stripping when in promiscuous mode, i.e.:
> > http://git.kernel.org/?p=linux/kernel/git/torvalds/linux-2.6.git;a=commit;h=5f6c01819979afbfec7e0b15fe52371b8eed87e8
> > 
> > However, at this point it is more or less random which drivers do
> > this.  It would obviously be much better if it were consistent.
> 
> My understanding is this. Hardware VLAN tagging and stripping can always be
> enabled. The kernel passes 802.1Q information along with the stripped
> header to libpcap which reassembles the original header where necessary.
> Works for me.
> 
> Hardware VLAN filtering, on the other hand, must be disabled in promiscuous
> mode. But doing that in the driver makes no difference now as the current
> VLAN code drops the packets so preserved before they are passed to the pcap
> interface. That appears to be a bug.

Agreed

Could you try following patch, based on net-next-2.6 ?

diff --git a/net/8021q/vlan_core.c b/net/8021q/vlan_core.c
index 0eb486d..fabdedb 100644
--- a/net/8021q/vlan_core.c
+++ b/net/8021q/vlan_core.c
@@ -101,7 +101,7 @@ vlan_gro_common(struct napi_struct *napi, struct vlan_group *grp,
 
 	if (vlan_dev)
 		skb->dev = vlan_dev;
-	else if (vlan_id)
+	else if (vlan_id && !(skb->dev->flags & IFF_PROMISC))
 		goto drop;
 
 	for (p = napi->gro_list; p; p = p->next) {