netdev - Re: [PATCH net-next v2 3/6] tsnep: Support XDP BPF program setup

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Date:   Thu, 8 Dec 2022 16:43:24 -0800
From:   Saeed Mahameed <saeed@...nel.org>
To:     Gerhard Engleder <gerhard@...leder-embedded.com>
Cc:     netdev@...r.kernel.org, bpf@...r.kernel.org, davem@...emloft.net,
        kuba@...nel.org, edumazet@...gle.com, pabeni@...hat.com,
        ast@...nel.org, daniel@...earbox.net, hawk@...nel.org,
        john.fastabend@...il.com
Subject: Re: [PATCH net-next v2 3/6] tsnep: Support XDP BPF program setup

On 08 Dec 06:40, Gerhard Engleder wrote:
>Implement setup of BPF programs for XDP RX path with command
>XDP_SETUP_PROG of ndo_bpf(). This is prework for XDP RX path support.
>
>Signed-off-by: Gerhard Engleder <gerhard@...leder-embedded.com>

[ ... ]

>+int tsnep_xdp_setup_prog(struct tsnep_adapter *adapter, struct bpf_prog *prog,
>+			 struct netlink_ext_ack *extack)
>+{
>+	struct net_device *dev = adapter->netdev;
>+	bool if_running = netif_running(dev);
>+	struct bpf_prog *old_prog;
>+
>+	if (if_running)
>+		tsnep_netdev_close(dev);
>+
>+	old_prog = xchg(&adapter->xdp_prog, prog);
>+	if (old_prog)
>+		bpf_prog_put(old_prog);
>+
>+	if (if_running)
>+		tsnep_netdev_open(dev);

this could fail silently, and then cause double free, when close ndo 
will be called, the stack won't be aware of the closed state..