[PATCH 6.1 212/215] bpf: Add table ID to bpf_fib_lookup BPF helper

Greg Kroah-Hartman
2024-03-04T21:52:23Z

From: Louis DeLosSantos <louis.delos.devel@gmail.com>

commit 8ad77e72caae22a1ddcfd0c03f2884929e93b7a4 upstream.

Add ability to specify routing table ID to the `bpf_fib_lookup` BPF
helper.

A new field `tbid` is added to `struct bpf_fib_lookup` used as
parameters to the `bpf_fib_lookup` BPF helper.

When the helper is called with the `BPF_FIB_LOOKUP_DIRECT` and
`BPF_FIB_LOOKUP_TBID` flags the `tbid` field in `struct bpf_fib_lookup`
will be used as the table ID for the fib lookup.

If the `tbid` does not exist the fib lookup will fail with
`BPF_FIB_LKUP_RET_NOT_FWDED`.

The `tbid` field becomes a union over the vlan related output fields
in `struct bpf_fib_lookup` and will be zeroed immediately after usage.

This functionality is useful in containerized environments.

For instance, if a CNI wants to dictate the next-hop for traffic leaving
a container it can create a container-specific routing table and perform
a fib lookup against this table in a "host-net-namespace-side" TC program.

This functionality also allows `ip rule` like functionality at the TC
layer, allowing an eBPF program to pick a routing table based on some
aspect of the sk_buff.

As a concrete use case, this feature will be used in Cilium's SRv6 L3VPN
datapath.

When egress traffic leaves a Pod an eBPF program attached by Cilium will
determine which VRF the egress traffic should target, and then perform a
FIB lookup in a specific table representing this VRF's FIB.

Signed-off-by: Louis DeLosSantos <louis.delos.devel@gmail.com>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Link: https://lore.kernel.org/bpf/20230505-bpf-add-tbid-fib-lookup-v2-1-0a31c22c748c@gmail.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
include/uapi/linux/bpf.h | 21 ++++++++++++++++++---
net/core/filter.c | 14 +++++++++++++-
tools/include/uapi/linux/bpf.h | 21 ++++++++++++++++++---
3 files changed, 49 insertions(+), 7 deletions(-)

--- a/include/uapi/linux/bpf.h
+++ b/include/uapi/linux/bpf.h
@@ -3109,6 +3109,10 @@ union bpf_attr {
* **BPF_FIB_LOOKUP_DIRECT**
* Do a direct table lookup vs full lookup using FIB
* rules.
+ * **BPF_FIB_LOOKUP_TBID**
+ * Used with BPF_FIB_LOOKUP_DIRECT.
+ * Use the routing table ID present in *params*->tbid
+ * for the fib lookup.
* **BPF_FIB_LOOKUP_OUTPUT**
* Perform lookup from an egress perspective (default is
* ingress).
@@ -6687,6 +6691,7 @@ enum {
BPF_FIB_LOOKUP_DIRECT = (1U << 0),
BPF_FIB_LOOKUP_OUTPUT = (1U << 1),
BPF_FIB_LOOKUP_SKIP_NEIGH = (1U << 2),
+ BPF_FIB_LOOKUP_TBID = (1U << 3),
};

enum {
@@ -6747,9 +6752,19 @@ struct bpf_fib_lookup {
__u32 ipv6_dst[4]; /* in6_addr; network order */
};

- /* output */
- __be16 h_vlan_proto;
- __be16 h_vlan_TCI;
+ union {
+ struct {
+ /* output */
+ __be16 h_vlan_proto;
+ __be16 h_vlan_TCI;
+ };
+ /* input: when accompanied with the
+ * 'BPF_FIB_LOOKUP_DIRECT | BPF_FIB_LOOKUP_TBID` flags, a
+ * specific routing table to use for the fib lookup.
+ */
+ __u32 tbid;
+ };
+
__u8 smac[6]; /* ETH_ALEN */
__u8 dmac[6]; /* ETH_ALEN */
};
--- a/net/core/filter.c
+++ b/net/core/filter.c
@@ -5752,6 +5752,12 @@ static int bpf_ipv4_fib_lookup(struct ne
u32 tbid = l3mdev_fib_table_rcu(dev) ? : RT_TABLE_MAIN;
struct fib_table *tb;

+ if (flags & BPF_FIB_LOOKUP_TBID) {
+ tbid = params->tbid;
+ /* zero out for vlan output */
+ params->tbid = 0;
+ }
+
tb = fib_get_table(net, tbid);
if (unlikely(!tb))
return BPF_FIB_LKUP_RET_NOT_FWDED;
@@ -5885,6 +5891,12 @@ static int bpf_ipv6_fib_lookup(struct ne
u32 tbid = l3mdev_fib_table_rcu(dev) ? : RT_TABLE_MAIN;
struct fib6_table *tb;

+ if (flags & BPF_FIB_LOOKUP_TBID) {
+ tbid = params->tbid;
+ /* zero out for vlan output */
+ params->tbid = 0;
+ }
+
tb = ipv6_stub->fib6_get_table(net, tbid);
if (unlikely(!tb))
return BPF_FIB_LKUP_RET_NOT_FWDED;
@@ -5957,7 +5969,7 @@ set_fwd_params:
#endif

#define BPF_FIB_LOOKUP_MASK (BPF_FIB_LOOKUP_DIRECT | BPF_FIB_LOOKUP_OUTPUT | \
- BPF_FIB_LOOKUP_SKIP_NEIGH)
+ BPF_FIB_LOOKUP_SKIP_NEIGH | BPF_FIB_LOOKUP_TBID)

BPF_CALL_4(bpf_xdp_fib_lookup, struct xdp_buff *, ctx,
struct bpf_fib_lookup *, params, int, plen, u32, flags)
--- a/tools/include/uapi/linux/bpf.h
+++ b/tools/include/uapi/linux/bpf.h
@@ -3109,6 +3109,10 @@ union bpf_attr {
* **BPF_FIB_LOOKUP_DIRECT**
* Do a direct table lookup vs full lookup using FIB
* rules.
+ * **BPF_FIB_LOOKUP_TBID**
+ * Used with BPF_FIB_LOOKUP_DIRECT.
+ * Use the routing table ID present in *params*->tbid
+ * for the fib lookup.
* **BPF_FIB_LOOKUP_OUTPUT**
* Perform lookup from an egress perspective (default is
* ingress).
@@ -6687,6 +6691,7 @@ enum {
BPF_FIB_LOOKUP_DIRECT = (1U << 0),
BPF_FIB_LOOKUP_OUTPUT = (1U << 1),
BPF_FIB_LOOKUP_SKIP_NEIGH = (1U << 2),
+ BPF_FIB_LOOKUP_TBID = (1U << 3),
};

enum {
@@ -6747,9 +6752,19 @@ struct bpf_fib_lookup {
__u32 ipv6_dst[4]; /* in6_addr; network order */
};

- /* output */
- __be16 h_vlan_proto;
- __be16 h_vlan_TCI;
+ union {
+ struct {
+ /* output */
+ __be16 h_vlan_proto;
+ __be16 h_vlan_TCI;
+ };
+ /* input: when accompanied with the
+ * 'BPF_FIB_LOOKUP_DIRECT | BPF_FIB_LOOKUP_TBID` flags, a
+ * specific routing table to use for the fib lookup.
+ */
+ __u32 tbid;
+ };
+
__u8 smac[6]; /* ETH_ALEN */
__u8 dmac[6]; /* ETH_ALEN */
};