Linux Ethernet Bridging - Sep 2017 - [Bridge] [PATCH net] bridge: switchdev: Clear forward mark when transmitting packet

Commit 6bc506b4fb06 ("bridge: switchdev: Add forward mark support for
stacked devices") added the 'offload_fwd_mark' bit to the skb in
order
to allow drivers to indicate to the bridge driver that they already
forwarded the packet in L2.

In case the bit is set, before transmitting the packet from each port,
the port's mark is compared with the mark stored in the skb's control
block. If both marks are equal, we know the packet arrived from a switch
device that already forwarded the packet and it's not re-transmitted.

However, if the packet is transmitted from the bridge device itself
(e.g., br0), we should clear the 'offload_fwd_mark' bit as the mark
stored in the skb's control block isn't valid.

This scenario can happen in rare cases where a packet was trapped during
L3 forwarding and forwarded by the kernel to a bridge device.

Fixes: 6bc506b4fb06 ("bridge: switchdev: Add forward mark support for
stacked devices")
Signed-off-by: Ido Schimmel <idosch at mellanox.com>
Reported-by: Yotam Gigi <yotamg at mellanox.com>
Tested-by: Yotam Gigi <yotamg at mellanox.com>
Reviewed-by: Jiri Pirko <jiri at mellanox.com>
---
 net/bridge/br_device.c | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/net/bridge/br_device.c b/net/bridge/br_device.c
index 861ae2a165f4..5a7be3bddfa9 100644
--- a/net/bridge/br_device.c
+++ b/net/bridge/br_device.c
@@ -53,6 +53,9 @@ netdev_tx_t br_dev_xmit(struct sk_buff *skb, struct net_device
*dev)
 	brstats->tx_bytes += skb->len;
 	u64_stats_update_end(&brstats->syncp);
 
+#ifdef CONFIG_NET_SWITCHDEV
+	skb->offload_fwd_mark = 0;
+#endif
 	BR_INPUT_SKB_CB(skb)->brdev = dev;
 
 	skb_reset_mac_header(skb);
-- 
2.13.5

On 01/09/17 12:22, Ido Schimmel wrote:
> Commit 6bc506b4fb06 ("bridge: switchdev: Add forward mark support for
> stacked devices") added the 'offload_fwd_mark' bit to the skb
in order
> to allow drivers to indicate to the bridge driver that they already
> forwarded the packet in L2.
> 
> In case the bit is set, before transmitting the packet from each port,
> the port's mark is compared with the mark stored in the skb's
control
> block. If both marks are equal, we know the packet arrived from a switch
> device that already forwarded the packet and it's not re-transmitted.
> 
> However, if the packet is transmitted from the bridge device itself
> (e.g., br0), we should clear the 'offload_fwd_mark' bit as the mark
> stored in the skb's control block isn't valid.
> 
> This scenario can happen in rare cases where a packet was trapped during
> L3 forwarding and forwarded by the kernel to a bridge device.
> 
> Fixes: 6bc506b4fb06 ("bridge: switchdev: Add forward mark support for
stacked devices")
> Signed-off-by: Ido Schimmel <idosch at mellanox.com>
> Reported-by: Yotam Gigi <yotamg at mellanox.com>
> Tested-by: Yotam Gigi <yotamg at mellanox.com>
> Reviewed-by: Jiri Pirko <jiri at mellanox.com>
> ---
>  net/bridge/br_device.c | 3 +++
>  1 file changed, 3 insertions(+)
> 
> diff --git a/net/bridge/br_device.c b/net/bridge/br_device.c
> index 861ae2a165f4..5a7be3bddfa9 100644
> --- a/net/bridge/br_device.c
> +++ b/net/bridge/br_device.c
> @@ -53,6 +53,9 @@ netdev_tx_t br_dev_xmit(struct sk_buff *skb, struct
net_device *dev)
>  	brstats->tx_bytes += skb->len;
>  	u64_stats_update_end(&brstats->syncp);
>  
> +#ifdef CONFIG_NET_SWITCHDEV
> +	skb->offload_fwd_mark = 0;
> +#endif
>  	BR_INPUT_SKB_CB(skb)->brdev = dev;
>  
>  	skb_reset_mac_header(skb);
> 
Good catch, just one minor nit since there is already an ifdef
switchdev/else in br_private.h, why not make this a helper and avoid the
ifdef/endif in here ? Currently there is no ifdef switchdev anywhere else.

Thanks,
 Nik

From: Ido Schimmel <idosch at mellanox.com>
Date: Fri,  1 Sep 2017 12:22:25 +0300
> Commit 6bc506b4fb06 ("bridge: switchdev: Add forward mark support for
> stacked devices") added the 'offload_fwd_mark' bit to the skb
in order
> to allow drivers to indicate to the bridge driver that they already
> forwarded the packet in L2.
> 
> In case the bit is set, before transmitting the packet from each port,
> the port's mark is compared with the mark stored in the skb's
control
> block. If both marks are equal, we know the packet arrived from a switch
> device that already forwarded the packet and it's not re-transmitted.
> 
> However, if the packet is transmitted from the bridge device itself
> (e.g., br0), we should clear the 'offload_fwd_mark' bit as the mark
> stored in the skb's control block isn't valid.
> 
> This scenario can happen in rare cases where a packet was trapped during
> L3 forwarding and forwarded by the kernel to a bridge device.
> 
> Fixes: 6bc506b4fb06 ("bridge: switchdev: Add forward mark support for
stacked devices")
> Signed-off-by: Ido Schimmel <idosch at mellanox.com>
> Reported-by: Yotam Gigi <yotamg at mellanox.com>
> Tested-by: Yotam Gigi <yotamg at mellanox.com>
> Reviewed-by: Jiri Pirko <jiri at mellanox.com>
Applied and queued up for -stable, thanks.