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Date:   Thu, 18 Jul 2019 20:34:56 -0700 (PDT)
Message-Id: <20190718.203456.202734701056640827.davem@davemloft.net>
To:     edumazet@google.com
Cc:     netdev@vger.kernel.org, eric.dumazet@gmail.com, brakmo@fb.com,
        ncardwell@google.com
Subject: Re: [PATCH net] tcp: fix tcp_set_congestion_control() use from bpf
 hook
From:   David Miller <davem@davemloft.net>
In-Reply-To: <20190719022814.233056-1-edumazet@google.com>
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From: Eric Dumazet <edumazet@google.com>
Date: Thu, 18 Jul 2019 19:28:14 -0700

> 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@google.com>
> Cc: Lawrence Brakmo <brakmo@fb.com>
> Reported-by: Neal Cardwell <ncardwell@google.com>

Applied and queued up for -stable.