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Message-ID: <3ebc429e-c8fb-5f1b-29bb-3285352c0831@iogearbox.net>
Date: Wed, 18 Apr 2018 22:59:27 +0200
From: Daniel Borkmann <daniel@...earbox.net>
To: Eyal Birger <eyal.birger@...il.com>, netdev@...r.kernel.org
Cc: shmulik@...anetworks.com, ast@...nel.org, fw@...len.de,
steffen.klassert@...unet.com
Subject: Re: [PATCH bpf-next 1/2] bpf: add helper for getting xfrm states
On 04/17/2018 06:48 AM, Eyal Birger wrote:
> This commit introduces a helper which allows fetching xfrm state
> parameters by eBPF programs attached to TC.
>
> Prototype:
> bpf_skb_get_xfrm_state(skb, index, xfrm_state, size, flags)
>
> skb: pointer to skb
> index: the index in the skb xfrm_state secpath array
> xfrm_state: pointer to 'struct bpf_xfrm_state'
> size: size of 'struct bpf_xfrm_state'
> flags: reserved for future extensions
>
> The helper returns 0 on success. Non zero if no xfrm state at the index
> is found - or non exists at all.
>
> struct bpf_xfrm_state currently includes the SPI, peer IPv4/IPv6
> address and the reqid; it can be further extended by adding elements to
> its end - indicating the populated fields by the 'size' argument -
> keeping backwards compatibility.
>
> Typical usage:
>
> struct bpf_xfrm_state x = {};
> bpf_skb_get_xfrm_state(skb, 0, &x, sizeof(x), 0);
> ...
>
> Signed-off-by: Eyal Birger <eyal.birger@...il.com>
Patch looks good to me, two comments below:
> ---
> include/uapi/linux/bpf.h | 25 ++++++++++++++++++++++++-
> net/core/filter.c | 46 ++++++++++++++++++++++++++++++++++++++++++++++
> 2 files changed, 70 insertions(+), 1 deletion(-)
>
> diff --git a/include/uapi/linux/bpf.h b/include/uapi/linux/bpf.h
> index c5ec897..132e172 100644
> --- a/include/uapi/linux/bpf.h
> +++ b/include/uapi/linux/bpf.h
> @@ -755,6 +755,15 @@ union bpf_attr {
> * @addr: pointer to struct sockaddr to bind socket to
> * @addr_len: length of sockaddr structure
> * Return: 0 on success or negative error code
> + *
> + * int bpf_skb_get_xfrm_state(skb, index, xfrm_state, size, flags)
> + * retrieve XFRM state
> + * @skb: pointer to skb
> + * @index: index of the xfrm state in the secpath
> + * @key: pointer to 'struct bpf_xfrm_state'
> + * @size: size of 'struct bpf_xfrm_state'
> + * @flags: room for future extensions
> + * Return: 0 on success or negative error
> */
> #define __BPF_FUNC_MAPPER(FN) \
> FN(unspec), \
> @@ -821,7 +830,8 @@ union bpf_attr {
> FN(msg_apply_bytes), \
> FN(msg_cork_bytes), \
> FN(msg_pull_data), \
> - FN(bind),
> + FN(bind), \
> + FN(skb_get_xfrm_state),
>
> /* integer value in 'imm' field of BPF_CALL instruction selects which helper
> * function eBPF program intends to call
> @@ -927,6 +937,19 @@ struct bpf_tunnel_key {
> __u32 tunnel_label;
> };
>
> +/* user accessible mirror of in-kernel xfrm_state.
> + * new fields can only be added to the end of this structure
> + */
> +struct bpf_xfrm_state {
> + __u32 reqid;
> + __u32 spi;
> + __u16 family;
> + union {
> + __u32 remote_ipv4;
> + __u32 remote_ipv6[4];
> + };
> +};
> +
> /* Generic BPF return codes which all BPF program types may support.
> * The values are binary compatible with their TC_ACT_* counter-part to
> * provide backwards compatibility with existing SCHED_CLS and SCHED_ACT
> diff --git a/net/core/filter.c b/net/core/filter.c
> index d31aff9..c06600a 100644
> --- a/net/core/filter.c
> +++ b/net/core/filter.c
> @@ -57,6 +57,7 @@
> #include <net/sock_reuseport.h>
> #include <net/busy_poll.h>
> #include <net/tcp.h>
> +#include <net/xfrm.h>
> #include <linux/bpf_trace.h>
>
> /**
> @@ -3703,6 +3704,49 @@ static const struct bpf_func_proto bpf_bind_proto = {
> .arg3_type = ARG_CONST_SIZE,
> };
>
> +BPF_CALL_5(bpf_skb_get_xfrm_state, struct sk_buff *, skb, u32, index,
> + struct bpf_xfrm_state *, to, u32, size, u64, flags)
> +{
> +#ifdef CONFIG_XFRM
> + const struct sec_path *sp = skb_sec_path(skb);
> + const struct xfrm_state *x;
> +
> + if (!sp || index >= sp->len)
This should be something like: if (!sp || unlikely(index >= sp->len || flags))
Such that we unconditionally bail out on any flags currently, since this is
reserved for future use and anything non-zero would be invalid and rejected
until we start extending it.
> + goto err_clear;
> +
> + x = sp->xvec[index];
> +
> + if (unlikely(size != sizeof(struct bpf_xfrm_state)))
> + goto err_clear;
> +
> + to->reqid = x->props.reqid;
> + to->spi = be32_to_cpu(x->id.spi);
> + to->family = x->props.family;
> + if (to->family == AF_INET6) {
> + memcpy(to->remote_ipv6, x->props.saddr.a6,
> + sizeof(to->remote_ipv6));
> + } else {
> + to->remote_ipv4 = be32_to_cpu(x->props.saddr.a4);
> + }
> +
> + return 0;
> +err_clear:
> +#endif
> + memset(to, 0, size);
> + return -EINVAL;
> +}
> +
> +static const struct bpf_func_proto bpf_skb_get_xfrm_state_proto = {
> + .func = bpf_skb_get_xfrm_state,
> + .gpl_only = false,
> + .ret_type = RET_INTEGER,
> + .arg1_type = ARG_PTR_TO_CTX,
> + .arg2_type = ARG_ANYTHING,
> + .arg3_type = ARG_PTR_TO_UNINIT_MEM,
> + .arg4_type = ARG_CONST_SIZE,
> + .arg5_type = ARG_ANYTHING,
> +};
> +
> static const struct bpf_func_proto *
> bpf_base_func_proto(enum bpf_func_id func_id)
> {
> @@ -3844,6 +3888,8 @@ tc_cls_act_func_proto(enum bpf_func_id func_id, const struct bpf_prog *prog)
> return &bpf_get_socket_cookie_proto;
> case BPF_FUNC_get_socket_uid:
> return &bpf_get_socket_uid_proto;
> + case BPF_FUNC_skb_get_xfrm_state:
> + return &bpf_skb_get_xfrm_state_proto;
Potentially, on kernels with !CONFIG_XFRM, you might want to let the program
bail out at program verification phase already? Thus it would become ...
#ifdef CONFIG_XFRM
case BPF_FUNC_skb_get_xfrm_state:
return &bpf_skb_get_xfrm_state_proto;
#endif
... where you'd also wrap the helper + state_proto in CONFIG_XFRM.
> default:
> return bpf_base_func_proto(func_id);
> }
>
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