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Date: Thu, 15 Oct 2020 10:27:12 -0600
From: David Ahern <dsahern@...il.com>
To: Toke Høiland-Jørgensen <toke@...hat.com>,
Daniel Borkmann <daniel@...earbox.net>
Cc: David Ahern <dsahern@...nel.org>, netdev@...r.kernel.org,
bpf@...r.kernel.org
Subject: Re: [PATCH RFC bpf-next 1/2] bpf_redirect_neigh: Support supplying
the nexthop as a helper parameter
On 10/15/20 9:46 AM, Toke Høiland-Jørgensen wrote:
> diff --git a/include/uapi/linux/bpf.h b/include/uapi/linux/bpf.h
> index bf5a99d803e4..980cc1363be8 100644
> --- a/include/uapi/linux/bpf.h
> +++ b/include/uapi/linux/bpf.h
> @@ -3677,15 +3677,19 @@ union bpf_attr {
> * Return
> * The id is returned or 0 in case the id could not be retrieved.
> *
> - * long bpf_redirect_neigh(u32 ifindex, u64 flags)
> + * long bpf_redirect_neigh(u32 ifindex, struct bpf_redir_neigh *params, int plen, u64 flags)
why not fold ifindex into params? with params and plen this should be
extensible later if needed.
A couple of nits below that caught me eye.
> * Description
> * Redirect the packet to another net device of index *ifindex*
> * and fill in L2 addresses from neighboring subsystem. This helper
> * is somewhat similar to **bpf_redirect**\ (), except that it
> * populates L2 addresses as well, meaning, internally, the helper
> - * performs a FIB lookup based on the skb's networking header to
> - * get the address of the next hop and then relies on the neighbor
> - * lookup for the L2 address of the nexthop.
> + * relies on the neighbor lookup for the L2 address of the nexthop.
> + *
> + * The helper will perform a FIB lookup based on the skb's
> + * networking header to get the address of the next hop, unless
> + * this is supplied by the caller in the *params* argument. The
> + * *plen* argument indicates the len of *params* and should be set
> + * to 0 if *params* is NULL.
> *
> * The *flags* argument is reserved and must be 0. The helper is
> * currently only supported for tc BPF program types, and enabled
> @@ -4906,6 +4910,17 @@ struct bpf_fib_lookup {
> __u8 dmac[6]; /* ETH_ALEN */
> };
>
> +struct bpf_redir_neigh {
> + /* network family for lookup (AF_INET, AF_INET6)
> + */
second line for the comment is not needed.
> + __u8 nh_family;
> + /* network address of nexthop; skips fib lookup to find gateway */
> + union {
> + __be32 ipv4_nh;
> + __u32 ipv6_nh[4]; /* in6_addr; network order */
> + };
> +};
> +
> enum bpf_task_fd_type {
> BPF_FD_TYPE_RAW_TRACEPOINT, /* tp name */
> BPF_FD_TYPE_TRACEPOINT, /* tp name */
> diff --git a/net/core/filter.c b/net/core/filter.c
> index c5e2a1c5fd8d..d073031a3a61 100644
> --- a/net/core/filter.c
> +++ b/net/core/filter.c
> @@ -2165,12 +2165,11 @@ static int __bpf_redirect(struct sk_buff *skb, struct net_device *dev,
> }
>
> #if IS_ENABLED(CONFIG_IPV6)
> -static int bpf_out_neigh_v6(struct net *net, struct sk_buff *skb)
> +static int bpf_out_neigh_v6(struct net *net, struct sk_buff *skb,
> + struct net_device *dev, const struct in6_addr *nexthop)
> {
> - struct dst_entry *dst = skb_dst(skb);
> - struct net_device *dev = dst->dev;
> u32 hh_len = LL_RESERVED_SPACE(dev);
> - const struct in6_addr *nexthop;
> + struct dst_entry *dst = NULL;
> struct neighbour *neigh;
>
> if (dev_xmit_recursion()) {
> @@ -2196,8 +2195,11 @@ static int bpf_out_neigh_v6(struct net *net, struct sk_buff *skb)
> }
>
> rcu_read_lock_bh();
> - nexthop = rt6_nexthop(container_of(dst, struct rt6_info, dst),
> - &ipv6_hdr(skb)->daddr);
> + if (!nexthop) {
> + dst = skb_dst(skb);
> + nexthop = rt6_nexthop(container_of(dst, struct rt6_info, dst),
> + &ipv6_hdr(skb)->daddr);
> + }
> neigh = ip_neigh_gw6(dev, nexthop);
> if (likely(!IS_ERR(neigh))) {
> int ret;
> @@ -2210,36 +2212,46 @@ static int bpf_out_neigh_v6(struct net *net, struct sk_buff *skb)
> return ret;
> }
> rcu_read_unlock_bh();
> - IP6_INC_STATS(dev_net(dst->dev),
> - ip6_dst_idev(dst), IPSTATS_MIB_OUTNOROUTES);
> + if (dst)
> + IP6_INC_STATS(dev_net(dst->dev),
> + ip6_dst_idev(dst), IPSTATS_MIB_OUTNOROUTES);
> out_drop:
> kfree_skb(skb);
> return -ENETDOWN;
> }
>
> -static int __bpf_redirect_neigh_v6(struct sk_buff *skb, struct net_device *dev)
> +static int __bpf_redirect_neigh_v6(struct sk_buff *skb, struct net_device *dev,
> + struct bpf_nh_params *nh)
> {
> const struct ipv6hdr *ip6h = ipv6_hdr(skb);
> + struct in6_addr *nexthop = NULL;
> struct net *net = dev_net(dev);
> int err, ret = NET_XMIT_DROP;
> - struct dst_entry *dst;
> - struct flowi6 fl6 = {
> - .flowi6_flags = FLOWI_FLAG_ANYSRC,
> - .flowi6_mark = skb->mark,
> - .flowlabel = ip6_flowinfo(ip6h),
> - .flowi6_oif = dev->ifindex,
> - .flowi6_proto = ip6h->nexthdr,
> - .daddr = ip6h->daddr,
> - .saddr = ip6h->saddr,
> - };
>
> - dst = ipv6_stub->ipv6_dst_lookup_flow(net, NULL, &fl6, NULL);
> - if (IS_ERR(dst))
> - goto out_drop;
> + if (!nh->nh_family) {
> + struct dst_entry *dst;
reverse xmas tree ordering
> + struct flowi6 fl6 = {
> + .flowi6_flags = FLOWI_FLAG_ANYSRC,
> + .flowi6_mark = skb->mark,
> + .flowlabel = ip6_flowinfo(ip6h),
> + .flowi6_oif = dev->ifindex,
> + .flowi6_proto = ip6h->nexthdr,
> + .daddr = ip6h->daddr,
> + .saddr = ip6h->saddr,
> + };
> +
> + dst = ipv6_stub->ipv6_dst_lookup_flow(net, NULL, &fl6, NULL);
> + if (IS_ERR(dst))
> + goto out_drop;
>
> - skb_dst_set(skb, dst);
> + skb_dst_set(skb, dst);
> + } else if (nh->nh_family == AF_INET6) {
> + nexthop = &nh->ipv6_nh;
> + } else {
> + goto out_drop;
> + }
>
> - err = bpf_out_neigh_v6(net, skb);
> + err = bpf_out_neigh_v6(net, skb, dev, nexthop);
> if (unlikely(net_xmit_eval(err)))
> dev->stats.tx_errors++;
> else
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