netdev - Re: [PATCH net] tcp: fix tcp_set_congestion

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Date:   Thu, 18 Jul 2019 22:50:07 -0400
From:   Neal Cardwell <ncardwell@...gle.com>
To:     Eric Dumazet <edumazet@...gle.com>
Cc:     "David S . Miller" <davem@...emloft.net>,
        netdev <netdev@...r.kernel.org>,
        Eric Dumazet <eric.dumazet@...il.com>,
        Lawrence Brakmo <brakmo@...com>
Subject: Re: [PATCH net] tcp: fix tcp_set_congestion_control() use from bpf hook

On Thu, Jul 18, 2019 at 10:28 PM Eric Dumazet <edumazet@...gle.com> wrote:
>
> Neal reported incorrect use of ns_capable() from bpf hook.
>
> bpf_setsockopt(...TCP_CONGESTION...)
>   -> tcp_set_congestion_control()
>    -> ns_capable(sock_net(sk)->user_ns, CAP_NET_ADMIN)
>     -> ns_capable_common()
>      -> current_cred()
>       -> rcu_dereference_protected(current->cred, 1)
>
> Accessing 'current' in bpf context makes no sense, since packets
> are processed from softirq context.
>
> As Neal stated : The capability check in tcp_set_congestion_control()
> was written assuming a system call context, and then was reused from
> a BPF call site.
>
> The fix is to add a new parameter to tcp_set_congestion_control(),
> so that the ns_capable() call is only performed under the right
> context.
>
> Fixes: 91b5b21c7c16 ("bpf: Add support for changing congestion control")
> Signed-off-by: Eric Dumazet <edumazet@...gle.com>
> Cc: Lawrence Brakmo <brakmo@...com>
> Reported-by: Neal Cardwell <ncardwell@...gle.com>
> ---

Acked-by: Neal Cardwell <ncardwell@...gle.com>

Thanks, Eric!

neal