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Date: Thu, 26 Mar 2020 10:24:48 +0000
From: Lorenz Bauer <lmb@...udflare.com>
To: Joe Stringer <joe@...d.net.nz>
Cc: bpf <bpf@...r.kernel.org>, Networking <netdev@...r.kernel.org>,
Daniel Borkmann <daniel@...earbox.net>,
Alexei Starovoitov <ast@...nel.org>,
Eric Dumazet <eric.dumazet@...il.com>,
Martin Lau <kafai@...com>
Subject: Re: [PATCHv2 bpf-next 1/5] bpf: Add socket assign support
On Wed, 25 Mar 2020 at 05:57, Joe Stringer <joe@...d.net.nz> 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/include/net/sock.h b/include/net/sock.h
> index b5cca7bae69b..2613d21a667a 100644
> --- a/include/net/sock.h
> +++ b/include/net/sock.h
> @@ -1657,6 +1657,7 @@ struct sk_buff *sock_omalloc(struct sock *sk, unsigned long size,
> void skb_orphan_partial(struct sk_buff *skb);
> void sock_rfree(struct sk_buff *skb);
> void sock_efree(struct sk_buff *skb);
> +void sock_pfree(struct sk_buff *skb);
> #ifdef CONFIG_INET
> void sock_edemux(struct sk_buff *skb);
> #else
> @@ -2526,6 +2527,12 @@ void sock_net_set(struct sock *sk, struct net *net)
> write_pnet(&sk->sk_net, net);
> }
>
> +static inline bool
> +skb_sk_is_prefetched(struct sk_buff *skb)
> +{
> + return skb->destructor == sock_pfree;
> +}
> +
> static inline struct sock *skb_steal_sock(struct sk_buff *skb)
> {
> if (skb->sk) {
> diff --git a/include/uapi/linux/bpf.h b/include/uapi/linux/bpf.h
> index 5d01c5c7e598..0c6f151deebe 100644
> --- a/include/uapi/linux/bpf.h
> +++ b/include/uapi/linux/bpf.h
> @@ -2950,6 +2950,28 @@ union bpf_attr {
> * restricted to raw_tracepoint bpf programs.
> * Return
> * 0 on success, or a negative error in case of failure.
> + *
> + * int bpf_sk_assign(struct sk_buff *skb, struct bpf_sock *sk, u64 flags)
> + * Description
> + * Assign the *sk* to the *skb*. When combined with appropriate
> + * routing configuration to receive the packet towards the socket,
> + * will cause *skb* to be delivered to the specified socket.
> + * Subsequent redirection of *skb* via **bpf_redirect**\ (),
> + * **bpf_clone_redirect**\ () or other methods outside of BPF may
> + * interfere with successful delivery to the socket.
> + *
> + * This operation is only valid from TC ingress path.
> + *
> + * The *flags* argument must be zero.
> + * Return
> + * 0 on success, or a negative errno in case of failure.
> + *
> + * * **-EINVAL** Unsupported flags specified.
> + * * **-ENETUNREACH** Socket is unreachable (wrong netns).
> + * * **-ENOENT** Socket is unavailable for assignment.
> + * * **-EOPNOTSUPP** Unsupported operation, for example a
> + * call from outside of TC ingress.
> + * * **-ESOCKTNOSUPPORT** Socket type not supported (reuseport).
> */
> #define __BPF_FUNC_MAPPER(FN) \
> FN(unspec), \
> @@ -3073,7 +3095,8 @@ union bpf_attr {
> FN(jiffies64), \
> FN(read_branch_records), \
> FN(get_ns_current_pid_tgid), \
> - FN(xdp_output),
> + FN(xdp_output), \
> + FN(sk_assign),
>
> /* integer value in 'imm' field of BPF_CALL instruction selects which helper
> * function eBPF program intends to call
> diff --git a/net/core/filter.c b/net/core/filter.c
> index 96350a743539..f7f9b6631f75 100644
> --- a/net/core/filter.c
> +++ b/net/core/filter.c
> @@ -5860,6 +5860,35 @@ static const struct bpf_func_proto bpf_tcp_gen_syncookie_proto = {
> .arg5_type = ARG_CONST_SIZE,
> };
>
> +BPF_CALL_3(bpf_sk_assign, struct sk_buff *, skb, struct sock *, sk, u64, flags)
> +{
> + if (flags != 0)
> + return -EINVAL;
> + if (!skb_at_tc_ingress(skb))
> + return -EOPNOTSUPP;
> + if (unlikely(sk->sk_reuseport))
> + return -ESOCKTNOSUPPORT;
> + if (unlikely(dev_net(skb->dev) != sock_net(sk)))
> + return -ENETUNREACH;
> + if (unlikely(!refcount_inc_not_zero(&sk->sk_refcnt)))
> + return -ENOENT;
> +
> + skb_orphan(skb);
> + skb->sk = sk;
> + skb->destructor = sock_pfree;
> +
> + return 0;
> +}
Follow up to my email re UDP tests: it seems like the helper doesn't check
that the sk is TCP, hence I assumed that you want to add support for
both in the same series.
Also, is it possible to check that the sk protocol matches skb protocol?
> +
> +static const struct bpf_func_proto bpf_sk_assign_proto = {
> + .func = bpf_sk_assign,
> + .gpl_only = false,
> + .ret_type = RET_INTEGER,
> + .arg1_type = ARG_PTR_TO_CTX,
> + .arg2_type = ARG_PTR_TO_SOCK_COMMON,
> + .arg3_type = ARG_ANYTHING,
> +};
> +
> #endif /* CONFIG_INET */
>
> bool bpf_helper_changes_pkt_data(void *func)
> @@ -6153,6 +6182,8 @@ tc_cls_act_func_proto(enum bpf_func_id func_id, const struct bpf_prog *prog)
> return &bpf_skb_ecn_set_ce_proto;
> case BPF_FUNC_tcp_gen_syncookie:
> return &bpf_tcp_gen_syncookie_proto;
> + case BPF_FUNC_sk_assign:
> + return &bpf_sk_assign_proto;
> #endif
> default:
> return bpf_base_func_proto(func_id);
> diff --git a/net/core/sock.c b/net/core/sock.c
> index 0fc8937a7ff4..cfaf60267360 100644
> --- a/net/core/sock.c
> +++ b/net/core/sock.c
> @@ -2071,6 +2071,15 @@ void sock_efree(struct sk_buff *skb)
> }
> EXPORT_SYMBOL(sock_efree);
>
> +/* Buffer destructor for prefetch/receive path where reference count may
> + * not be held, e.g. for listen sockets.
> + */
> +void sock_pfree(struct sk_buff *skb)
> +{
> + sock_edemux(skb);
> +}
> +EXPORT_SYMBOL(sock_pfree);
> +
> kuid_t sock_i_uid(struct sock *sk)
> {
> kuid_t uid;
> diff --git a/net/ipv4/ip_input.c b/net/ipv4/ip_input.c
> index aa438c6758a7..b0c244af1e4d 100644
> --- a/net/ipv4/ip_input.c
> +++ b/net/ipv4/ip_input.c
> @@ -509,7 +509,8 @@ static struct sk_buff *ip_rcv_core(struct sk_buff *skb, struct net *net)
> IPCB(skb)->iif = skb->skb_iif;
>
> /* Must drop socket now because of tproxy. */
> - skb_orphan(skb);
> + if (!skb_sk_is_prefetched(skb))
> + skb_orphan(skb);
>
> return skb;
>
> diff --git a/net/ipv6/ip6_input.c b/net/ipv6/ip6_input.c
> index 7b089d0ac8cd..e96304d8a4a7 100644
> --- a/net/ipv6/ip6_input.c
> +++ b/net/ipv6/ip6_input.c
> @@ -285,7 +285,8 @@ static struct sk_buff *ip6_rcv_core(struct sk_buff *skb, struct net_device *dev,
> rcu_read_unlock();
>
> /* Must drop socket now because of tproxy. */
> - skb_orphan(skb);
> + if (!skb_sk_is_prefetched(skb))
> + skb_orphan(skb);
>
> return skb;
> err:
> 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)
> + skb_orphan(skb);
> rcu_read_unlock();
>
> /* A BPF program may overwrite the default action opcode.
> diff --git a/tools/include/uapi/linux/bpf.h b/tools/include/uapi/linux/bpf.h
> index 5d01c5c7e598..0c6f151deebe 100644
> --- a/tools/include/uapi/linux/bpf.h
> +++ b/tools/include/uapi/linux/bpf.h
> @@ -2950,6 +2950,28 @@ union bpf_attr {
> * restricted to raw_tracepoint bpf programs.
> * Return
> * 0 on success, or a negative error in case of failure.
> + *
> + * int bpf_sk_assign(struct sk_buff *skb, struct bpf_sock *sk, u64 flags)
> + * Description
> + * Assign the *sk* to the *skb*. When combined with appropriate
> + * routing configuration to receive the packet towards the socket,
> + * will cause *skb* to be delivered to the specified socket.
> + * Subsequent redirection of *skb* via **bpf_redirect**\ (),
> + * **bpf_clone_redirect**\ () or other methods outside of BPF may
> + * interfere with successful delivery to the socket.
> + *
> + * This operation is only valid from TC ingress path.
> + *
> + * The *flags* argument must be zero.
> + * Return
> + * 0 on success, or a negative errno in case of failure.
> + *
> + * * **-EINVAL** Unsupported flags specified.
> + * * **-ENETUNREACH** Socket is unreachable (wrong netns).
> + * * **-ENOENT** Socket is unavailable for assignment.
> + * * **-EOPNOTSUPP** Unsupported operation, for example a
> + * call from outside of TC ingress.
> + * * **-ESOCKTNOSUPPORT** Socket type not supported (reuseport).
> */
> #define __BPF_FUNC_MAPPER(FN) \
> FN(unspec), \
> @@ -3073,7 +3095,8 @@ union bpf_attr {
> FN(jiffies64), \
> FN(read_branch_records), \
> FN(get_ns_current_pid_tgid), \
> - FN(xdp_output),
> + FN(xdp_output), \
> + FN(sk_assign),
>
> /* integer value in 'imm' field of BPF_CALL instruction selects which helper
> * function eBPF program intends to call
> --
> 2.20.1
>
--
Lorenz Bauer | Systems Engineer
6th Floor, County Hall/The Riverside Building, SE1 7PB, UK
www.cloudflare.com
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