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bpf: Add table ID to bpf_fib_lookup BPF helper

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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
This commit is contained in:
Louis DeLosSantos
2023-05-31 15:38:48 -04:00
committed by Andrii Nakryiko
parent fa1a18d38b
commit f02ec78083
1 changed files with 18 additions and 3 deletions
Download Patch File Download Diff File Expand all files Collapse all files

21
include/uapi/linux/bpf.h
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@@ -3177,6 +3177,10 @@ 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).
@@ -6831,6 +6835,7 @@ 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 {
@@ -6891,9 +6896,19 @@ 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 */
};