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

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Date:   Fri, 9 Dec 2022 09:06:00 +0100
From:   Gerhard Engleder <gerhard@...leder-embedded.com>
To:     Saeed Mahameed <saeed@...nel.org>
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 09.12.22 01:43, Saeed Mahameed wrote:
>> +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..

I will ensure that no double free will happen when ndo_close is called.

Gerhard