netdev - Re: [PATCH net-next] bpf: pass sk to helper functions

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Message-ID: <CAF=yD-KKi8ihZHp0K7bgJZ1v4ez4n12gkzxL=YWZ1=Jpb62Arw@mail.gmail.com>
Date:   Tue, 11 Apr 2017 13:31:49 -0400
From:   Willem de Bruijn <willemdebruijn.kernel@...il.com>
To:     Eric Dumazet <eric.dumazet@...il.com>
Cc:     Network Development <netdev@...r.kernel.org>,
        Alexei Starovoitov <ast@...com>,
        Daniel Borkmann <daniel@...earbox.net>,
        David Miller <davem@...emloft.net>,
        Willem de Bruijn <willemb@...gle.com>
Subject: Re: [PATCH net-next] bpf: pass sk to helper functions

On Tue, Apr 11, 2017 at 12:51 PM, Eric Dumazet <eric.dumazet@...il.com> wrote:
> On Tue, 2017-04-11 at 12:22 -0400, Willem de Bruijn wrote:
>> From: Willem de Bruijn <willemb@...gle.com>
>>
>> BPF helper functions access socket fields through skb->sk. This is not
>> set in ingress cgroup and socket filters. The association is only made
>> in skb_set_owner_r once the filter has accepted the packet. Sk is
>> available as socket lookup has taken place.
>>
>> Temporarily set skb->sk to sk in these cases.
>>
>> Signed-off-by: Willem de Bruijn <willemb@...gle.com>
>> ---
>>  kernel/bpf/cgroup.c | 4 +++-
>>  net/core/filter.c   | 6 +++++-
>>  2 files changed, 8 insertions(+), 2 deletions(-)
>>
>> diff --git a/kernel/bpf/cgroup.c b/kernel/bpf/cgroup.c
>> index da0f53690295..a2c387e433a4 100644
>> --- a/kernel/bpf/cgroup.c
>> +++ b/kernel/bpf/cgroup.c
>> @@ -154,7 +154,7 @@ int __cgroup_bpf_update(struct cgroup *cgrp, struct cgroup *parent,
>>
>>  /**
>>   * __cgroup_bpf_run_filter_skb() - Run a program for packet filtering
>> - * @sk: The socken sending or receiving traffic
>> + * @sk: The socket sending or receiving traffic
>>   * @skb: The skb that is being sent or received
>>   * @type: The type of program to be exectuted
>>   *
>> @@ -190,9 +190,11 @@ int __cgroup_bpf_run_filter_skb(struct sock *sk,
>>       if (prog) {
>>               unsigned int offset = skb->data - skb_network_header(skb);
>>
>
> It would be nice to not touch sk. swap() is a bit overkill here I think.
>
>         struct sock *save_sk = skb->sk;
>
>         skb->sk = sk;
>
>
>> +             swap(skb->sk, sk);
>>               __skb_push(skb, offset);
>>               ret = bpf_prog_run_save_cb(prog, skb) == 1 ? 0 : -EPERM;
>>               __skb_pull(skb, offset);
>> +             swap(skb->sk, sk);
>
>         skb->sk = save_sk;
>
>>       }

Thanks. I'll send a v2.

>>
>
>
>