netdev - Re: [net-next] tipc: improve throughput between nodes in netns

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Date:   Mon, 21 Oct 2019 19:40:47 -0700
From:   Eric Dumazet <eric.dumazet@...il.com>
To:     Hoang Le <hoang.h.le@...tech.com.au>, jon.maloy@...csson.com,
        maloy@...jonn.com, tipc-discussion@...ts.sourceforge.net,
        netdev@...r.kernel.org
Subject: Re: [net-next] tipc: improve throughput between nodes in netns



On 10/21/19 7:20 PM, Hoang Le wrote:
>  	n->net = net;
>  	n->capabilities = capabilities;
> +	n->pnet = NULL;
> +	for_each_net_rcu(tmp) {

This does not scale well, if say you have a thousand netns ?

> +		tn_peer = net_generic(tmp, tipc_net_id);
> +		if (!tn_peer)
> +			continue;
> +		/* Integrity checking whether node exists in namespace or not */
> +		if (tn_peer->net_id != tn->net_id)
> +			continue;
> +		if (memcmp(peer_id, tn_peer->node_id, NODE_ID_LEN))
> +			continue;
> +
> +		hash_chk = tn_peer->random;
> +		hash_chk ^= net_hash_mix(&init_net);

Why the xor with net_hash_mix(&init_net) is needed ?

> +		hash_chk ^= net_hash_mix(tmp);
> +		if (hash_chk ^ hash_mixes)
> +			continue;
> +		n->pnet = tmp;
> +		break;
> +	}


How can we set n->pnet without increasing netns ->count ?

Using check_net() later might trigger an use-after-free.