On 01/31/2019 12:51 AM, Peter Oskolkov wrote:
> This patch implements BPF_LWT_ENCAP_IP mode in bpf_lwt_push_encap
> BPF helper. It enables BPF programs (specifically, BPF_PROG_TYPE_LWT_IN
> and BPF_PROG_TYPE_LWT_XMIT prog types) to add IP encapsulation headers
> to packets (e.g. IP/GRE, GUE, IPIP).
>
> This is useful when thousands of different short-lived flows should be
> encapped, each with different and dynamically determined destination.
> Although lwtunnels can be used in some of these scenarios, the ability
> to dynamically generate encap headers adds more flexibility, e.g.
> when routing depends on the state of the host (reflected in global bpf
> maps).
>
> Signed-off-by: Peter Oskolkov <p...@google.com>
> ---
> include/net/lwtunnel.h | 3 +++
> net/core/filter.c | 3 ++-
> net/core/lwt_bpf.c | 59 ++++++++++++++++++++++++++++++++++++++++++
> 3 files changed, 64 insertions(+), 1 deletion(-)
>
> diff --git a/include/net/lwtunnel.h b/include/net/lwtunnel.h
> index 33fd9ba7e0e5..f0973eca8036 100644
> --- a/include/net/lwtunnel.h
> +++ b/include/net/lwtunnel.h
> @@ -126,6 +126,8 @@ int lwtunnel_cmp_encap(struct lwtunnel_state *a, struct
> lwtunnel_state *b);
> int lwtunnel_output(struct net *net, struct sock *sk, struct sk_buff *skb);
> int lwtunnel_input(struct sk_buff *skb);
> int lwtunnel_xmit(struct sk_buff *skb);
> +int bpf_lwt_push_ip_encap(struct sk_buff *skb, void *hdr, u32 len,
> + bool ingress);
>
> static inline void lwtunnel_set_redirect(struct dst_entry *dst)
> {
> @@ -138,6 +140,7 @@ static inline void lwtunnel_set_redirect(struct dst_entry
> *dst)
> dst->input = lwtunnel_input;
> }
> }
> +
> #else
>
> static inline void lwtstate_free(struct lwtunnel_state *lws)
> diff --git a/net/core/filter.c b/net/core/filter.c
> index 27d3fbe4b77b..de6bd4b4e0a3 100644
> --- a/net/core/filter.c
> +++ b/net/core/filter.c
> @@ -73,6 +73,7 @@
> #include <linux/seg6_local.h>
> #include <net/seg6.h>
> #include <net/seg6_local.h>
> +#include <net/lwtunnel.h>
>
> /**
> * sk_filter_trim_cap - run a packet through a socket filter
> @@ -4804,7 +4805,7 @@ static int bpf_push_seg6_encap(struct sk_buff *skb, u32
> type, void *hdr, u32 len
> static int bpf_push_ip_encap(struct sk_buff *skb, void *hdr, u32 len,
> bool ingress)
> {
> - return -EINVAL; /* Implemented in the next patch. */
> + return bpf_lwt_push_ip_encap(skb, hdr, len, ingress);
> }
>
> BPF_CALL_4(bpf_lwt_in_push_encap, struct sk_buff *, skb, u32, type, void *,
> hdr,
> diff --git a/net/core/lwt_bpf.c b/net/core/lwt_bpf.c
> index a648568c5e8f..6a6e9acab73d 100644
> --- a/net/core/lwt_bpf.c
> +++ b/net/core/lwt_bpf.c
> @@ -390,6 +390,65 @@ static const struct lwtunnel_encap_ops bpf_encap_ops = {
> .owner = THIS_MODULE,
> };
>
> +int bpf_lwt_push_ip_encap(struct sk_buff *skb, void *hdr, u32 len, bool
> ingress)
> +{
> + struct iphdr *iph;
> + bool ipv4;
> + int err;
> +
> + if (unlikely(len < sizeof(struct iphdr) || len > LWT_BPF_MAX_HEADROOM))
> + return -EINVAL;
> +
> + /* validate protocol and length */
> + iph = (struct iphdr *)hdr;
> + if (iph->version == 4) {
> + ipv4 = true;
> + if (unlikely(len < iph->ihl * 4))
> + return -EINVAL;
> + } else if (iph->version == 6) {
> + ipv4 = false;
> + if (unlikely(len < sizeof(struct ipv6hdr)))
> + return -EINVAL;
> + } else {
> + return -EINVAL;
> + }
> +
> + if (ingress)
> + err = skb_cow_head(skb, len + skb->mac_len);
> + else
> + err = skb_cow_head(skb,
> + len + LL_RESERVED_SPACE(skb_dst(skb)->dev));
> + if (unlikely(err))
> + return err;
> +
> + /* push the encap headers and fix pointers */
> + skb_reset_inner_headers(skb);
> + skb->encapsulation = 1;
> + skb_push(skb, len);
> + if (ingress)
> + skb_postpush_rcsum(skb, iph, len);
> + skb_reset_network_header(skb);
> + memcpy(skb_network_header(skb), hdr, len);
> + bpf_compute_data_pointers(skb);
Does this work transparently with GSO as well or would we need to
update shared info for this (like in nat64 case, for example)?
> + if (ipv4) {
> + skb->protocol = htons(ETH_P_IP);
> + iph = ip_hdr(skb);
> + if (iph->ihl * 4 < len)
> + skb_set_transport_header(skb, iph->ihl * 4);
> +
> + if (!iph->check)
> + iph->check = ip_fast_csum((unsigned char *)iph,
> + iph->ihl);
> + } else {
> + skb->protocol = htons(ETH_P_IPV6);
> + if (sizeof(struct ipv6hdr) < len)
> + skb_set_transport_header(skb, sizeof(struct ipv6hdr));
> + }
> +
> + return 0;
> +}
> +
> static int __init bpf_lwt_init(void)
> {
> return lwtunnel_encap_add_ops(&bpf_encap_ops, LWTUNNEL_ENCAP_BPF);
>
