Linux Ethernet Bridging - Oct 2013 - [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
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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
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On Tue, 15 Oct 2013 00:20:10 +0200
Antonio Quartulli <antonio@meshcoding.com> wrote:
> 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,
> 
> 
The patch content is fine, but it needs necessary ifdef''s.
I would also prefer to have the clean done as a function that can be stubbed out
like the other bridge netfilter stuff.

On Tue, 15 Oct 2013 00:20:10 +0200
Antonio Quartulli <antonio at meshcoding.com> wrote:
> 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,
> 
> 
The patch content is fine, but it needs necessary ifdef's.
I would also prefer to have the clean done as a function that can be stubbed out
like the other bridge netfilter stuff.