David Ahern
2020-Jul-31 17:27 UTC
[Bridge] [PATCH net] net: bridge: clear bridge's private skb space on xmit
On 7/31/20 10:26 AM, Nikolay Aleksandrov wrote:> We need to clear all of the bridge private skb variables as they can be > stale due to the packet being recirculated through the stack and then > transmitted through the bridge device. Similar memset is already done on > bridge's input. We've seen cases where proxyarp_replied was 1 on routed > multicast packets transmitted through the bridge to ports with neigh > suppress which were getting dropped. Same thing can in theory happen with > the port isolation bit as well. > > Fixes: 821f1b21cabb ("bridge: add new BR_NEIGH_SUPPRESS port flag to suppress arp and nd flood") > Signed-off-by: Nikolay Aleksandrov <nikolay at cumulusnetworks.com> > --- > net/bridge/br_device.c | 2 ++ > 1 file changed, 2 insertions(+) > > diff --git a/net/bridge/br_device.c b/net/bridge/br_device.c > index 8c7b78f8bc23..9a2fb4aa1a10 100644 > --- a/net/bridge/br_device.c > +++ b/net/bridge/br_device.c > @@ -36,6 +36,8 @@ netdev_tx_t br_dev_xmit(struct sk_buff *skb, struct net_device *dev) > const unsigned char *dest; > u16 vid = 0; > > + memset(skb->cb, 0, sizeof(struct br_input_skb_cb)); > + > rcu_read_lock(); > nf_ops = rcu_dereference(nf_br_ops); > if (nf_ops && nf_ops->br_dev_xmit_hook(skb)) { >What's the performance hit of doing this on every packet? Can you just set a flag that tells the code to reset on recirculation? Seems like br_input_skb_cb has space for that.
Nikolay Aleksandrov
2020-Jul-31 17:37 UTC
[Bridge] [PATCH net] net: bridge: clear bridge's private skb space on xmit
On 31/07/2020 20:27, David Ahern wrote:> On 7/31/20 10:26 AM, Nikolay Aleksandrov wrote: >> We need to clear all of the bridge private skb variables as they can be >> stale due to the packet being recirculated through the stack and then >> transmitted through the bridge device. Similar memset is already done on >> bridge's input. We've seen cases where proxyarp_replied was 1 on routed >> multicast packets transmitted through the bridge to ports with neigh >> suppress which were getting dropped. Same thing can in theory happen with >> the port isolation bit as well. >> >> Fixes: 821f1b21cabb ("bridge: add new BR_NEIGH_SUPPRESS port flag to suppress arp and nd flood") >> Signed-off-by: Nikolay Aleksandrov <nikolay at cumulusnetworks.com> >> --- >> net/bridge/br_device.c | 2 ++ >> 1 file changed, 2 insertions(+) >> >> diff --git a/net/bridge/br_device.c b/net/bridge/br_device.c >> index 8c7b78f8bc23..9a2fb4aa1a10 100644 >> --- a/net/bridge/br_device.c >> +++ b/net/bridge/br_device.c >> @@ -36,6 +36,8 @@ netdev_tx_t br_dev_xmit(struct sk_buff *skb, struct net_device *dev) >> const unsigned char *dest; >> u16 vid = 0; >> >> + memset(skb->cb, 0, sizeof(struct br_input_skb_cb)); >> + >> rcu_read_lock(); >> nf_ops = rcu_dereference(nf_br_ops); >> if (nf_ops && nf_ops->br_dev_xmit_hook(skb)) { >> > > What's the performance hit of doing this on every packet? > > Can you just set a flag that tells the code to reset on recirculation? > Seems like br_input_skb_cb has space for that. >Virtually non-existent, we had a patch that turned that field into a 16 byte field so that is really 2 8 byte stores. It is already cache hot, we could initialize each individual field separately as br_input does. I don't want to waste flags on such thing, this makes it future-proof and I'll remove the individual field zeroing later which will alleviate the cost further.