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Date: Fri, 31 Jul 2020 20:37:50 +0300 From: Nikolay Aleksandrov <nikolay@...ulusnetworks.com> To: David Ahern <dsahern@...il.com>, netdev@...r.kernel.org Cc: bridge@...ts.linux-foundation.org, roopa@...ulusnetworks.com, davem@...emloft.net Subject: Re: [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@...ulusnetworks.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.
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