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Date: Thu, 19 Apr 2018 01:02:03 +0300
From: Eyal Birger <eyal.birger@...il.com>
To: Daniel Borkmann <daniel@...earbox.net>
Cc: netdev@...r.kernel.org
Subject: Re: [PATCH bpf-next 1/2] bpf: add helper for getting xfrm states
On Wed, 18 Apr 2018 22:59:27 +0200
Daniel Borkmann <daniel@...earbox.net> wrote:
> 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:
Thanks! I incorporated your suggestions in v2.
Eyal.
>
> > ---
> > 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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