From: Eric Dumazet <eduma...@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 <eduma...@google.com>
> Cc: Lawrence Brakmo <bra...@fb.com>
> Reported-by: Neal Cardwell <ncardw...@google.com>
Applied and queued up for -stable.
