netdev - Re: [PATCHv2 bpf-next 1/5] bpf: Add socket assign support

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Message-ID: <20200326062317.ofhr2o7azamwhaxf@kafai-mbp>
Date:   Wed, 25 Mar 2020 23:23:17 -0700
From:   Martin KaFai Lau <kafai@...com>
To:     Joe Stringer <joe@...d.net.nz>
CC:     <bpf@...r.kernel.org>, <netdev@...r.kernel.org>,
        <daniel@...earbox.net>, <ast@...nel.org>, <eric.dumazet@...il.com>,
        <lmb@...udflare.com>
Subject: Re: [PATCHv2 bpf-next 1/5] bpf: Add socket assign support

On Tue, Mar 24, 2020 at 10:57:41PM -0700, Joe Stringer wrote:
> Add support for TPROXY via a new bpf helper, bpf_sk_assign().
> 
> This helper requires the BPF program to discover the socket via a call
> to bpf_sk*_lookup_*(), then pass this socket to the new helper. The
> helper takes its own reference to the socket in addition to any existing
> reference that may or may not currently be obtained for the duration of
> BPF processing. For the destination socket to receive the traffic, the
> traffic must be routed towards that socket via local route. The
> simplest example route is below, but in practice you may want to route
> traffic more narrowly (eg by CIDR):
> 
>   $ ip route add local default dev lo
> 
> This patch avoids trying to introduce an extra bit into the skb->sk, as
> that would require more invasive changes to all code interacting with
> the socket to ensure that the bit is handled correctly, such as all
> error-handling cases along the path from the helper in BPF through to
> the orphan path in the input. Instead, we opt to use the destructor
> variable to switch on the prefetch of the socket.
> 
> Signed-off-by: Joe Stringer <joe@...d.net.nz>
> ---
> v2: Use skb->destructor to determine socket prefetch usage instead of
>       introducing a new metadata_dst
>     Restrict socket assign to same netns as TC device
>     Restrict assigning reuseport sockets
>     Adjust commit wording
> v1: Initial version
> ---
>  include/net/sock.h             |  7 +++++++
>  include/uapi/linux/bpf.h       | 25 ++++++++++++++++++++++++-
>  net/core/filter.c              | 31 +++++++++++++++++++++++++++++++
>  net/core/sock.c                |  9 +++++++++
>  net/ipv4/ip_input.c            |  3 ++-
>  net/ipv6/ip6_input.c           |  3 ++-
>  net/sched/act_bpf.c            |  2 ++
>  tools/include/uapi/linux/bpf.h | 25 ++++++++++++++++++++++++-
>  8 files changed, 101 insertions(+), 4 deletions(-)
> 

[ ... ]

> diff --git a/net/sched/act_bpf.c b/net/sched/act_bpf.c
> index 46f47e58b3be..6c7ed8fcc909 100644
> --- a/net/sched/act_bpf.c
> +++ b/net/sched/act_bpf.c
> @@ -53,6 +53,8 @@ static int tcf_bpf_act(struct sk_buff *skb, const struct tc_action *act,
>  		bpf_compute_data_pointers(skb);
>  		filter_res = BPF_PROG_RUN(filter, skb);
>  	}
> +	if (filter_res != TC_ACT_OK)
Should skb_sk_is_prefetched() be checked also?

> +		skb_orphan(skb);
>  	rcu_read_unlock();
>  
>  	/* A BPF program may overwrite the default action opcode.