netdev - Re: [PATCH] bonding: Fix corrupted queue

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Date:	Fri, 08 Jun 2012 07:57:37 +0200
From:	Eric Dumazet <eric.dumazet@...il.com>
To:	Tom Herbert <therbert@...gle.com>
Cc:	davem@...emloft.net, netdev@...r.kernel.org
Subject: Re: [PATCH] bonding: Fix corrupted queue_mapping

On Thu, 2012-06-07 at 22:05 -0700, Tom Herbert wrote:
> In the transmit path of the bonding driver, skb->cb is used to
> stash the skb->queue_mapping so that the bonding device can set its
> own queue mapping.  This value becomes corrupted since the skb->cb is
> also used in __dev_xmit_skb.
> 
> When transmitting through bonding driver, bond_select_queue is
> called from dev_queue_xmit.  In bond_select_queue the original
> skb->queue_mapping is copied into skb->cb (via bond_queue_mapping)
> and skb->queue_mapping is overwritten with the bond driver queue.
> Subsequently in dev_queue_xmit, __dev_xmit_skb is called which writes
> the packet length into skb->cb, thereby overwriting the stashed
> queue mappping.  In bond_dev_queue_xmit (called from hard_start_xmit),
> the queue mapping for the skb is set to the stashed value which is now
> the skb length and hence is an invalid queue for the slave device.
> 
> Fix is to set bond_queue_mapping to skb->cb +
> sizeof((struct qdisc_skb_cb)
> 
> Signed-off-by: Tom Herbert <therbert@...gle.com>
> ---
>  drivers/net/bonding/bond_main.c |    4 +++-
>  1 files changed, 3 insertions(+), 1 deletions(-)
> 
> diff --git a/drivers/net/bonding/bond_main.c b/drivers/net/bonding/bond_main.c
> index 2ee8cf9..044c1c0 100644
> --- a/drivers/net/bonding/bond_main.c
> +++ b/drivers/net/bonding/bond_main.c
> @@ -76,6 +76,7 @@
>  #include <net/route.h>
>  #include <net/net_namespace.h>
>  #include <net/netns/generic.h>
> +#include <net/sch_generic.h>
>  #include "bonding.h"
>  #include "bond_3ad.h"
>  #include "bond_alb.h"
> @@ -381,7 +382,8 @@ struct vlan_entry *bond_next_vlan(struct bonding *bond, struct vlan_entry *curr)
>  	return next;
>  }
>  
> -#define bond_queue_mapping(skb) (*(u16 *)((skb)->cb))
> +#define bond_queue_mapping(skb) (*(u16 *)((skb)->cb + \
> +    sizeof(struct qdisc_skb_cb)))
>  
>  /**
>   * bond_dev_queue_xmit - Prepare skb for xmit.


Sorry this wont work in all cases.

Some qdisc also use skb->cb[]

maybe :

diff --git a/include/net/sch_generic.h b/include/net/sch_generic.h
index 55ce96b..47cbfa2 100644
--- a/include/net/sch_generic.h
+++ b/include/net/sch_generic.h
@@ -220,6 +220,7 @@ struct tcf_proto {
 
 struct qdisc_skb_cb {
 	unsigned int		pkt_len;
+	unsigned int		bond_queue_mapping;
 	unsigned char		data[24];
 };
 




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