tcp: fix tcp_set_congestion_control() use from bpf hook

Neal reported incorrect use of ns_capable() from bpf hook.

  -> 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

Fixes: 91b5b21c7c16 ("bpf: Add support for changing congestion control")
Signed-off-by: Eric Dumazet <>
Cc: Lawrence Brakmo <>
Reported-by: Neal Cardwell <>
Acked-by: Neal Cardwell <>
Acked-by: Lawrence Brakmo <>
Signed-off-by: David S. Miller <>
4 files changed