[PATCH] bridge: add ETH_HLEN to packet_length

[PATCH] bridge: add ETH_HLEN to packet_length

[Jon Mason]

In br_dev_queue_push_xmit, why is the check to drop mtu oversized
packets not checking for enough room for the impending ETH_HLEN size
skb_push?  In some code currently under development, we are seeing
skb_under_panic being called from the "skb_push(skb, ETH_HLEN)" in that
code.  It seems to me it would be better to drop those skbs than panic.
Attached is a patch to do this.

Thanks,
Jon

Signed-off-by: Jon Mason <jdmason@kudzu.us>

diff -r b1d36669f98d net/bridge/br_forward.c
--- a/net/bridge/br_forward.c	Mon Sep  4 03:00:04 2006 +0000
+++ b/net/bridge/br_forward.c	Thu Sep 14 13:18:04 2006 -0500
@@ -29,7 +29,8 @@ static inline int should_deliver(const s
 
 static inline unsigned packet_length(const struct sk_buff *skb)
 {
-	return skb->len - (skb->protocol == htons(ETH_P_8021Q) ? VLAN_HLEN : 0);
+	return skb->len - ETH_HLEN - 
+		(skb->protocol == htons(ETH_P_8021Q) ? VLAN_HLEN : 0);
 }
 
 int br_dev_queue_push_xmit(struct sk_buff *skb)

Re: [PATCH] bridge: add ETH_HLEN to packet_length

[Mika Penttilä]

Jon Mason wrote:
> In br_dev_queue_push_xmit, why is the check to drop mtu oversized
> packets not checking for enough room for the impending ETH_HLEN size
> skb_push?  In some code currently under development, we are seeing
> skb_under_panic being called from the "skb_push(skb, ETH_HLEN)" in that
> code.  It seems to me it would be better to drop those skbs than panic.
> Attached is a patch to do this.
>
> Thanks,
> Jon
>
> Signed-off-by: Jon Mason <jdmason@kudzu.us>
>
> diff -r b1d36669f98d net/bridge/br_forward.c
> --- a/net/bridge/br_forward.c	Mon Sep  4 03:00:04 2006 +0000
> +++ b/net/bridge/br_forward.c	Thu Sep 14 13:18:04 2006 -0500
> @@ -29,7 +29,8 @@ static inline int should_deliver(const s
>  
>  static inline unsigned packet_length(const struct sk_buff *skb)
>  {
> -	return skb->len - (skb->protocol == htons(ETH_P_8021Q) ? VLAN_HLEN : 0);
> +	return skb->len - ETH_HLEN - 
> +		(skb->protocol == htons(ETH_P_8021Q) ? VLAN_HLEN : 0);
>  }
>
>   
packet_length() is a wrong place to do that, mtu has nothing to do with 
skb headroom.

--Mika

Re: [PATCH] bridge: add ETH_HLEN to packet_length

[Jon Mason]

On Thu, Sep 14, 2006 at 11:53:48PM +0300, Mika Penttil? wrote:
> Jon Mason wrote:
> >In br_dev_queue_push_xmit, why is the check to drop mtu oversized
> >packets not checking for enough room for the impending ETH_HLEN size
> >skb_push?  In some code currently under development, we are seeing
> >skb_under_panic being called from the "skb_push(skb, ETH_HLEN)" in that
> >code.  It seems to me it would be better to drop those skbs than panic.
> >Attached is a patch to do this.
> >
> >Thanks,
> >Jon
> >
> >Signed-off-by: Jon Mason <jdmason@kudzu.us>
> >
> >diff -r b1d36669f98d net/bridge/br_forward.c
> >--- a/net/bridge/br_forward.c	Mon Sep  4 03:00:04 2006 +0000
> >+++ b/net/bridge/br_forward.c	Thu Sep 14 13:18:04 2006 -0500
> >@@ -29,7 +29,8 @@ static inline int should_deliver(const s
> > 
> > static inline unsigned packet_length(const struct sk_buff *skb)
> > {
> >-	return skb->len - (skb->protocol == htons(ETH_P_8021Q) ? VLAN_HLEN : 
> >0);
> >+	return skb->len - ETH_HLEN - 
> >+		(skb->protocol == htons(ETH_P_8021Q) ? VLAN_HLEN : 0);
> > }
> >
> >  
> packet_length() is a wrong place to do that, mtu has nothing to do with 
> skb headroom.

Oops, you are 100% correct.  So what would be the best way to handle
this, as a panic is pretty nasty?  Wouldn't it be better to check the
packet to see if there is sufficient headroom, BUG, and then drop it
(or allocate a new packet with sufficient headroom and proceed with
the skb_push)?  

Thanks,
Jon

> 
> --Mika
> 
> 

Re: [PATCH] bridge: add ETH_HLEN to packet_length

[Stephen Hemminger]

On Thu, 14 Sep 2006 13:27:54 -0500
Jon Mason <jdmason@kudzu.us> wrote:

> In br_dev_queue_push_xmit, why is the check to drop mtu oversized
> packets not checking for enough room for the impending ETH_HLEN size
> skb_push?  In some code currently under development, we are seeing
> skb_under_panic being called from the "skb_push(skb, ETH_HLEN)" in that
> code.  It seems to me it would be better to drop those skbs than panic.
> Attached is a patch to do this.
> 
> Thanks,
> Jon

This is bridge code, it assumes that any device that claims to be a
ethernet device has done the proper reservation. What device are
you using?