Stephen Hemminger
2013-Sep-26 21:32 UTC
[Bridge] [RFC net] bridge: clean the nf_bridge status when forwarding the skb
On Thu, 26 Sep 2013 23:16:48 +0200 Antonio Quartulli <antonio at open-mesh.com> wrote:> On Thu, Sep 26, 2013 at 02:10:21PM -0700, Stephen Hemminger wrote: > > On Thu, 26 Sep 2013 22:19:50 +0200 > > Antonio Quartulli <antonio at meshcoding.com> wrote: > > > > > From: Antonio Quartulli <antonio at open-mesh.com> > > > > > > Even if enslaving a bridge interface into another bridge is > > > forbidden, it is still possible to create a chain of > > > virtual interfaces including two distinct bridges. > > > > > > In this case, the skb entering the second bridge could have > > > the nf_bridge field already set due to a previous operation > > > and consequently lead to a wrong processing of the packet > > > itself. > > > > > > To prevent this behaviour release and set to NULL the > > > nf_bridge field of the skb when exiting the bridge interface. > > > > > > Signed-off-by: Antonio Quartulli <antonio at open-mesh.com> > > > --- > > > > > > I am not sure if this is a wanted behaviour or a real BUG. I found this > > > "misbehaviour" while testing batman-adv with the following configuration: > > > > > > - br0 (bridge interface) having bat0 and eth0 as slaves > > > - bat0 (which is a virtual interface provided by the batman-adv module and that > > > works similarly to a bridge - to some extends) having br1 as slave > > > - br1 (second bridge interface) having eth1 as slave > > > > > > Then follow these events: > > > - a broadcast packet arrives on eth0 > > > - the skb enters br0 and skb->nf_bridge gets initialised and used > > > - the skb enters bat0 and the packet *gets encapsulated in the batman-adv packet > > > which adds a batman-adv header and another Ethernet header* > > > - the skb enters br1 and gets ruined because nf_bridge_maybe_copy_header() (in > > > br_dev_queue_push_xmit()) will try to restore an header that does not make > > > sense anymore. > > > > > > With this patch the nf_bridge gets de-initialised before exiting br0 and > > > therefore it is processed properly inside br1: nf_bridge_maybe_copy_header() > > > does not take place at all because nf_bridge is never initialised (the packet is > > > non-IP since it is a batman-adv packet) > > > > > > To the developers of the bridge module I would like to ask: > > > 1) is skb->nf_bridge allowed to be non NULL when entering br_dev_xmit() ? If so, > > > when is this supposed to happen? > > > > > > 2) do you think this patch is logically correct but the nf_bridge release should > > > be done in batman-adv since it is the one re-encapsulating the packet? > > > > > > > > > I hope I have made the problem clear. > > > > > > Best regards, > > > > > > > > > net/bridge/br_forward.c | 5 +++++ > > > 1 file changed, 5 insertions(+) > > > > > > diff --git a/net/bridge/br_forward.c b/net/bridge/br_forward.c > > > index 4b81b14..65864bc 100644 > > > --- a/net/bridge/br_forward.c > > > +++ b/net/bridge/br_forward.c > > > @@ -49,6 +49,11 @@ int br_dev_queue_push_xmit(struct sk_buff *skb) > > > } else { > > > skb_push(skb, ETH_HLEN); > > > br_drop_fake_rtable(skb); > > > + > > > + /* clean the NF bridge data */ > > > + nf_bridge_put(skb->nf_bridge); > > > + skb->nf_bridge = NULL; > > > + > > > dev_queue_xmit(skb); > > > } > > > > > Regarding CONFIG_BRIDGE_NETFILTER you are right, thanks. > > > > > I think the header will also be garbage if bridge on bridge with netfilter is used. > > See nf_bridge_save_header. > > What header are you referring to? nf_bridge_save_header() saves the header in > skb->nf_bridge->data, which is freed during nf_bridge_put() (assuming > ->use reached 0). > >If bridge is stacked the original ether header will get overwritten by the second call to save_header.
Antonio Quartulli
2013-Sep-26 22:01 UTC
[Bridge] [RFC net] bridge: clean the nf_bridge status when forwarding the skb
On Thu, Sep 26, 2013 at 02:32:48PM -0700, Stephen Hemminger wrote:> > > > diff --git a/net/bridge/br_forward.c b/net/bridge/br_forward.c > > > > index 4b81b14..65864bc 100644 > > > > --- a/net/bridge/br_forward.c > > > > +++ b/net/bridge/br_forward.c > > > > @@ -49,6 +49,11 @@ int br_dev_queue_push_xmit(struct sk_buff *skb) > > > > } else { > > > > skb_push(skb, ETH_HLEN); > > > > br_drop_fake_rtable(skb); > > > > + > > > > + /* clean the NF bridge data */ > > > > + nf_bridge_put(skb->nf_bridge); > > > > + skb->nf_bridge = NULL; > > > > + > > > > dev_queue_xmit(skb); > > > > } > > > > > > > > Regarding CONFIG_BRIDGE_NETFILTER you are right, thanks. > > > > > > > > I think the header will also be garbage if bridge on bridge with netfilter is used. > > > See nf_bridge_save_header. > > > > What header are you referring to? nf_bridge_save_header() saves the header in > > skb->nf_bridge->data, which is freed during nf_bridge_put() (assuming > > ->use reached 0). > > > > > > If bridge is stacked the original ether header will get overwritten by the second > call to save_header.Sorry, but I am not getting what you mean (I am new to the code and it is late here..): save_header() will store the Ethernet header in nf_bridge->data for later recover (if needed). By freeing nf_bridge I also destroy this header copy. When the skb enters the second bridge, save_header() will save again the header in nf_bridge->data. But I don't see how this can create a problem. The problem I had before this patch comes from the fact that nf_bridge_copy_header() is invoked in the second bridge with the nf_bridge state of the first. This was overwriting my the packet Ethernet header with what the first invocation of save_header() stored in nf_bridge->data. But by unsetting nf_bridge I think I am preventing this from happening again. no? -- Antonio Quartulli -------------- next part -------------- A non-text attachment was scrubbed... Name: signature.asc Type: application/pgp-signature Size: 836 bytes Desc: Digital signature URL: <http://lists.linuxfoundation.org/pipermail/bridge/attachments/20130927/03860ae4/attachment-0001.sig>
Antonio Quartulli
2013-Oct-14 22:20 UTC
Re: [RFC net] bridge: clean the nf_bridge status when forwarding the skb
On Fri, Sep 27, 2013 at 12:01:43AM +0200, Antonio Quartulli wrote:> On Thu, Sep 26, 2013 at 02:32:48PM -0700, Stephen Hemminger wrote: > > > > > diff --git a/net/bridge/br_forward.c b/net/bridge/br_forward.c > > > > > index 4b81b14..65864bc 100644 > > > > > --- a/net/bridge/br_forward.c > > > > > +++ b/net/bridge/br_forward.c > > > > > @@ -49,6 +49,11 @@ int br_dev_queue_push_xmit(struct sk_buff *skb) > > > > > } else { > > > > > skb_push(skb, ETH_HLEN); > > > > > br_drop_fake_rtable(skb); > > > > > + > > > > > + /* clean the NF bridge data */ > > > > > + nf_bridge_put(skb->nf_bridge); > > > > > + skb->nf_bridge = NULL; > > > > > + > > > > > dev_queue_xmit(skb); > > > > > } > > > > > > > > > > > Regarding CONFIG_BRIDGE_NETFILTER you are right, thanks. > > > > > > > > > > > I think the header will also be garbage if bridge on bridge with netfilter is used. > > > > See nf_bridge_save_header. > > > > > > What header are you referring to? nf_bridge_save_header() saves the header in > > > skb->nf_bridge->data, which is freed during nf_bridge_put() (assuming > > > ->use reached 0). > > > > > > > > > > If bridge is stacked the original ether header will get overwritten by the second > > call to save_header. > > Sorry, but I am not getting what you mean (I am new to the code and it is late here..): > save_header() will store the Ethernet header in nf_bridge->data for > later recover (if needed). > > By freeing nf_bridge I also destroy this header copy. > > When the skb enters the second bridge, save_header() will save again the header > in nf_bridge->data. But I don''t see how this can create a problem. > > The problem I had before this patch comes from the fact that > nf_bridge_copy_header() is invoked in the second bridge with the nf_bridge state > of the first. This was overwriting my the packet Ethernet header with what the > first invocation of save_header() stored in nf_bridge->data. > > But by unsetting nf_bridge I think I am preventing this from happening again. > no?Hello Stephen, do you have other comments about this patch? I know it is rather difficult that a generic user hits this issue, but I''d like to see it fixed because other people using batman-adv may incur in this problem. Cheers, -- Antonio Quartulli