netdev - Re: [PATCH net-next v9 2/3] netdevsim: forward skbs from one connected port to another

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite for Android: free password hash cracker in your pocket

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <5d23bdfe-df0f-4048-b2d1-c0e025fd3efd@davidwei.uk>
Date: Mon, 12 Feb 2024 09:32:20 -0800
From: David Wei <dw@...idwei.uk>
To: Maciek Machnikowski <maciek@...hnikowski.net>,
 Jakub Kicinski <kuba@...nel.org>, Jiri Pirko <jiri@...nulli.us>,
 Sabrina Dubroca <sd@...asysnail.net>, netdev@...r.kernel.org
Cc: "David S. Miller" <davem@...emloft.net>,
 Eric Dumazet <edumazet@...gle.com>, Paolo Abeni <pabeni@...hat.com>
Subject: Re: [PATCH net-next v9 2/3] netdevsim: forward skbs from one
 connected port to another

On 2024-02-10 13:43, Maciek Machnikowski wrote:
> 
> 
> On 10/02/2024 01:32, David Wei wrote:
>> Forward skbs sent from one netdevsim port to its connected netdevsim
>> port using dev_forward_skb, in a spirit similar to veth.
>>
>> Add a tx_dropped variable to struct netdevsim, tracking the number of
>> skbs that could not be forwarded using dev_forward_skb().
>>
>> The xmit() function accessing the peer ptr is protected by an RCU read
>> critical section. The rcu_read_lock() is functionally redundant as since
>> v5.0 all softirqs are implicitly RCU read critical sections; but it is
>> useful for human readers.
>>
>> If another CPU is concurrently in nsim_destroy(), then it will first set
>> the peer ptr to NULL. This does not affect any existing readers that
>> dereferenced a non-NULL peer. Then, in unregister_netdevice(), there is
>> a synchronize_rcu() before the netdev is actually unregistered and
>> freed. This ensures that any readers i.e. xmit() that got a non-NULL
>> peer will complete before the netdev is freed.
>>
>> Any readers after the RCU_INIT_POINTER() but before synchronize_rcu()
>> will dereference NULL, making it safe.
>>
>> The codepath to nsim_destroy() and nsim_create() takes both the newly
>> added nsim_dev_list_lock and rtnl_lock. This makes it safe with
>> concurrent calls to linking two netdevsims together.
>>
>> Signed-off-by: David Wei <dw@...idwei.uk>
>> ---
>>  drivers/net/netdevsim/netdev.c    | 28 +++++++++++++++++++++++-----
>>  drivers/net/netdevsim/netdevsim.h |  1 +
>>  2 files changed, 24 insertions(+), 5 deletions(-)
>>
>> diff --git a/drivers/net/netdevsim/netdev.c b/drivers/net/netdevsim/netdev.c
>> index 9063f4f2971b..13d3e1536451 100644
>> --- a/drivers/net/netdevsim/netdev.c
>> +++ b/drivers/net/netdevsim/netdev.c
>> @@ -29,19 +29,37 @@
>>  static netdev_tx_t nsim_start_xmit(struct sk_buff *skb, struct net_device *dev)
>>  {
>>  	struct netdevsim *ns = netdev_priv(dev);
>> +	unsigned int len = skb->len;
>> +	struct netdevsim *peer_ns;
>> +	int ret = NETDEV_TX_OK;
>>  
>>  	if (!nsim_ipsec_tx(ns, skb))
>>  		goto out;
>>  
>> +	rcu_read_lock();
>> +	peer_ns = rcu_dereference(ns->peer);
>> +	if (!peer_ns)
>> +		goto out_stats;
> Change ret to NET_XMIT_DROP to correctly count packets as dropped

Linking and forwarding between two netdevsims is optional, so I don't
want to always return NET_XMIT_DROP.

> 
>> +
>> +	skb_tx_timestamp(skb);
>> +	if (unlikely(dev_forward_skb(peer_ns->netdev, skb) == NET_RX_DROP))
>> +		ret = NET_XMIT_DROP;
>> +
>> +out_stats:
>> +	rcu_read_unlock();
>>  	u64_stats_update_begin(&ns->syncp);
>> -	ns->tx_packets++;
>> -	ns->tx_bytes += skb->len;
>> +	if (ret == NET_XMIT_DROP) {
>> +		ns->tx_dropped++;
> add dev_kfree_skb(skb);

dev_forward_skb() frees the skb if dropped already.

> 
> Thanks,
> Maciek
> 
>> +	} else {
>> +		ns->tx_packets++;
>> +		ns->tx_bytes += len;
>> +	}
>>  	u64_stats_update_end(&ns->syncp);
>> +	return ret;
>>  
>>  out:
>>  	dev_kfree_skb(skb);
>> -
>> -	return NETDEV_TX_OK;
>> +	return ret;
>>  }
>>  
>>  static void nsim_set_rx_mode(struct net_device *dev)
>> @@ -70,6 +88,7 @@ nsim_get_stats64(struct net_device *dev, struct rtnl_link_stats64 *stats)
>>  		start = u64_stats_fetch_begin(&ns->syncp);
>>  		stats->tx_bytes = ns->tx_bytes;
>>  		stats->tx_packets = ns->tx_packets;
>> +		stats->tx_dropped = ns->tx_dropped;
>>  	} while (u64_stats_fetch_retry(&ns->syncp, start));
>>  }
>>  
>> @@ -302,7 +321,6 @@ static void nsim_setup(struct net_device *dev)
>>  	eth_hw_addr_random(dev);
>>  
>>  	dev->tx_queue_len = 0;
>> -	dev->flags |= IFF_NOARP;
>>  	dev->flags &= ~IFF_MULTICAST;
>>  	dev->priv_flags |= IFF_LIVE_ADDR_CHANGE |
>>  			   IFF_NO_QUEUE;
>> diff --git a/drivers/net/netdevsim/netdevsim.h b/drivers/net/netdevsim/netdevsim.h
>> index c8b45b0d955e..553c4b9b4f63 100644
>> --- a/drivers/net/netdevsim/netdevsim.h
>> +++ b/drivers/net/netdevsim/netdevsim.h
>> @@ -98,6 +98,7 @@ struct netdevsim {
>>  
>>  	u64 tx_packets;
>>  	u64 tx_bytes;
>> +	u64 tx_dropped;
>>  	struct u64_stats_sync syncp;
>>  
>>  	struct nsim_bus_dev *nsim_bus_dev;