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

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Date:   Thu, 18 Jul 2019 20:34:56 -0700 (PDT)
From:   David Miller <davem@...emloft.net>
To:     edumazet@...gle.com
Cc:     netdev@...r.kernel.org, eric.dumazet@...il.com, brakmo@...com,
        ncardwell@...gle.com
Subject: Re: [PATCH net] tcp: fix tcp_set_congestion_control() use from bpf
 hook

From: Eric Dumazet <edumazet@...gle.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@...gle.com>
> Cc: Lawrence Brakmo <brakmo@...com>
> Reported-by: Neal Cardwell <ncardwell@...gle.com>

Applied and queued up for -stable.