[PATCH bpf-next 3/4] bpf: Add BPF_FIB_LOOKUP_SKIP_NEIGH for bpf_fib_lookup

Martin KaFai Lau
2023-02-17T00:42:10Z

The bpf_fib_lookup() also looks up the neigh table.
This was done before bpf_redirect_neigh() was added.

In the use case that does not manage the neigh table
and requires bpf_fib_lookup() to lookup a fib to
decide if it needs to redirect or not, the bpf prog can
depend only on using bpf_redirect_neigh() to lookup the
neigh. It also keeps the neigh entries fresh and connected.

This patch adds a bpf_fib_lookup flag, SKIP_NEIGH, to avoid
the double neigh lookup when the bpf prog always call
bpf_redirect_neigh() to do the neigh lookup.

Signed-off-by: Martin KaFai Lau <martin.lau@kernel.org>
---
include/uapi/linux/bpf.h | 1 +
net/core/filter.c | 33 +++++++++++++++++++++++----------
tools/include/uapi/linux/bpf.h | 1 +
3 files changed, 25 insertions(+), 10 deletions(-)

diff --git a/include/uapi/linux/bpf.h b/include/uapi/linux/bpf.h
index 1503f61336b6..6c1956e36c97 100644
--- a/include/uapi/linux/bpf.h
+++ b/include/uapi/linux/bpf.h
@@ -6750,6 +6750,7 @@ struct bpf_raw_tracepoint_args {
enum {
BPF_FIB_LOOKUP_DIRECT = (1U << 0),
BPF_FIB_LOOKUP_OUTPUT = (1U << 1),
+ BPF_FIB_LOOKUP_SKIP_NEIGH = (1U << 2),
};

enum {
diff --git a/net/core/filter.c b/net/core/filter.c
index 8daaaf76ab15..08f0f21863bc 100644
--- a/net/core/filter.c
+++ b/net/core/filter.c
@@ -5723,10 +5723,8 @@ static const struct bpf_func_proto bpf_skb_get_xfrm_state_proto = {

#if IS_ENABLED(CONFIG_INET) || IS_ENABLED(CONFIG_IPV6)
static int bpf_fib_set_fwd_params(struct bpf_fib_lookup *params,
- const struct neighbour *neigh,
const struct net_device *dev, u32 mtu)
{
- memcpy(params->dmac, neigh->ha, ETH_ALEN);
memcpy(params->smac, dev->dev_addr, ETH_ALEN);
params->h_vlan_TCI = 0;
params->h_vlan_proto = 0;
@@ -5838,21 +5836,28 @@ static int bpf_ipv4_fib_lookup(struct net *net, struct bpf_fib_lookup *params,
if (likely(nhc->nhc_gw_family != AF_INET6)) {
if (nhc->nhc_gw_family)
params->ipv4_dst = nhc->nhc_gw.ipv4;
-
- neigh = __ipv4_neigh_lookup_noref(dev,
- (__force u32)params->ipv4_dst);
} else {
struct in6_addr *dst = (struct in6_addr *)params->ipv6_dst;

params->family = AF_INET6;
*dst = nhc->nhc_gw.ipv6;
- neigh = __ipv6_neigh_lookup_noref_stub(dev, dst);
}

+ if (flags & BPF_FIB_LOOKUP_SKIP_NEIGH)
+ goto set_fwd_params;
+
+ if (params->family == AF_INET6)
+ neigh = __ipv6_neigh_lookup_noref_stub(dev, params->ipv6_dst);
+ else
+ neigh = __ipv4_neigh_lookup_noref(dev,
+ (__force u32)params->ipv4_dst);
+
if (!neigh || !(neigh->nud_state & NUD_VALID))
return BPF_FIB_LKUP_RET_NO_NEIGH;
+ memcpy(params->dmac, neigh->ha, ETH_ALEN);

- return bpf_fib_set_fwd_params(params, neigh, dev, mtu);
+set_fwd_params:
+ return bpf_fib_set_fwd_params(params, dev, mtu);
}
#endif

@@ -5960,24 +5965,32 @@ static int bpf_ipv6_fib_lookup(struct net *net, struct bpf_fib_lookup *params,
params->rt_metric = res.f6i->fib6_metric;
params->ifindex = dev->ifindex;

+ if (flags & BPF_FIB_LOOKUP_SKIP_NEIGH)
+ goto set_fwd_params;
+
/* xdp and cls_bpf programs are run in RCU-bh so rcu_read_lock_bh is
* not needed here.
*/
neigh = __ipv6_neigh_lookup_noref_stub(dev, dst);
if (!neigh || !(neigh->nud_state & NUD_VALID))
return BPF_FIB_LKUP_RET_NO_NEIGH;
+ memcpy(params->dmac, neigh->ha, ETH_ALEN);

- return bpf_fib_set_fwd_params(params, neigh, dev, mtu);
+set_fwd_params:
+ return bpf_fib_set_fwd_params(params, dev, mtu);
}
#endif

+#define BPF_FIB_LOOKUP_MASK (BPF_FIB_LOOKUP_DIRECT | BPF_FIB_LOOKUP_OUTPUT | \
+ BPF_FIB_LOOKUP_SKIP_NEIGH)
+
BPF_CALL_4(bpf_xdp_fib_lookup, struct xdp_buff *, ctx,
struct bpf_fib_lookup *, params, int, plen, u32, flags)
{
if (plen < sizeof(*params))
return -EINVAL;

- if (flags & ~(BPF_FIB_LOOKUP_DIRECT | BPF_FIB_LOOKUP_OUTPUT))
+ if (flags & ~BPF_FIB_LOOKUP_MASK)
return -EINVAL;

switch (params->family) {
@@ -6015,7 +6028,7 @@ BPF_CALL_4(bpf_skb_fib_lookup, struct sk_buff *, skb,
if (plen < sizeof(*params))
return -EINVAL;

- if (flags & ~(BPF_FIB_LOOKUP_DIRECT | BPF_FIB_LOOKUP_OUTPUT))
+ if (flags & ~BPF_FIB_LOOKUP_MASK)
return -EINVAL;

if (params->tot_len)
diff --git a/tools/include/uapi/linux/bpf.h b/tools/include/uapi/linux/bpf.h
index 1503f61336b6..6c1956e36c97 100644
--- a/tools/include/uapi/linux/bpf.h
+++ b/tools/include/uapi/linux/bpf.h
@@ -6750,6 +6750,7 @@ struct bpf_raw_tracepoint_args {
enum {
BPF_FIB_LOOKUP_DIRECT = (1U << 0),
BPF_FIB_LOOKUP_OUTPUT = (1U << 1),
+ BPF_FIB_LOOKUP_SKIP_NEIGH = (1U << 2),
};

enum {
--
2.30.2