netdev - Re: [net 4/9] net/mlx5e: Fix refcount leak on kTLS RX resync

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Date:   Wed, 4 Nov 2020 14:59:27 -0800
From:   Jakub Kicinski <kuba@...nel.org>
To:     Saeed Mahameed <saeedm@...dia.com>
Cc:     "David S. Miller" <davem@...emloft.net>, <netdev@...r.kernel.org>,
        "Maxim Mikityanskiy" <maximmi@...lanox.com>,
        Tariq Toukan <tariqt@...dia.com>
Subject: Re: [net 4/9] net/mlx5e: Fix refcount leak on kTLS RX resync

On Tue, 3 Nov 2020 11:18:25 -0800 Saeed Mahameed wrote:
> From: Maxim Mikityanskiy <maximmi@...lanox.com>
> 
> On resync, the driver calls inet_lookup_established
> (__inet6_lookup_established) that increases sk_refcnt of the socket. To
> decrease it, the driver set skb->destructor to sock_edemux. However, it
> didn't work well, because the TCP stack also sets this destructor for
> early demux, and the refcount gets decreased only once

Why is the stack doing early_demux if there is already a socket
assigned? Or is it not early_demux but something else?
Can you point us at the code?

IPv4:
	if (net->ipv4.sysctl_ip_early_demux &&
	    !skb_dst(skb) &&
	    !skb->sk &&                              <============
	    !ip_is_fragment(iph)) {
		const struct net_protocol *ipprot;
		int protocol = iph->protocol;

		ipprot = rcu_dereference(inet_protos[protocol]);
		if (ipprot && (edemux = READ_ONCE(ipprot->early_demux))) {
			err = INDIRECT_CALL_2(edemux, tcp_v4_early_demux,
					      udp_v4_early_demux, skb);
			if (unlikely(err))
				goto drop_error;
			/* must reload iph, skb->head might have changed */
			iph = ip_hdr(skb);
		}
	}

IPv6:
	if (net->ipv4.sysctl_ip_early_demux && !skb_dst(skb) && skb->sk == NULL) {
                                                                ~~~~~~~~~~~~~~~
		const struct inet6_protocol *ipprot;

		ipprot = rcu_dereference(inet6_protos[ipv6_hdr(skb)->nexthdr]);
		if (ipprot && (edemux = READ_ONCE(ipprot->early_demux)))
			INDIRECT_CALL_2(edemux, tcp_v6_early_demux,
					udp_v6_early_demux, skb);
	}