On 5/25/23 7:27 AM, Louis DeLosSantos wrote:
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` flag and the
`tbid` field in `struct bpf_fib_lookup` is greater then 0, the `tbid`
field will be used as the table ID for the fib lookup.
I think table id 0 is legal in the kernel, right?
It is probably okay to consider table id 0 not supported to
simplify the user interface. But it would be great to
add some explanations in the commit message.
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@xxxxxxxxx>
---
include/uapi/linux/bpf.h | 17 ++++++++++++++---
net/core/filter.c | 12 ++++++++++++
tools/include/uapi/linux/bpf.h | 17 ++++++++++++++---
3 files changed, 40 insertions(+), 6 deletions(-)
diff --git a/include/uapi/linux/bpf.h b/include/uapi/linux/bpf.h
index 1bb11a6ee6676..2096fbb328a9b 100644
--- a/include/uapi/linux/bpf.h
+++ b/include/uapi/linux/bpf.h
@@ -3167,6 +3167,8 @@ union bpf_attr {
* **BPF_FIB_LOOKUP_DIRECT**
* Do a direct table lookup vs full lookup using FIB
* rules.
+ * If *params*->tbid is non-zero, this value designates
+ * a routing table ID to perform the lookup against.
* **BPF_FIB_LOOKUP_OUTPUT**
* Perform lookup from an egress perspective (default is
* ingress).
@@ -6881,9 +6883,18 @@ 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` flag, a
+ * specific routing table to use for the fib lookup.
+ */
+ __u32 tbid;
+ };
+
__u8 smac[6]; /* ETH_ALEN */
__u8 dmac[6]; /* ETH_ALEN */
};
diff --git a/net/core/filter.c b/net/core/filter.c
index 451b0ec7f2421..6f710aa0a54b3 100644
--- a/net/core/filter.c
+++ b/net/core/filter.c
@@ -5803,6 +5803,12 @@ static int bpf_ipv4_fib_lookup(struct net *net, struct bpf_fib_lookup *params,
u32 tbid = l3mdev_fib_table_rcu(dev) ? : RT_TABLE_MAIN;
struct fib_table *tb;
+ if (params->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;
@@ -5936,6 +5942,12 @@ static int bpf_ipv6_fib_lookup(struct net *net, struct bpf_fib_lookup *params,
u32 tbid = l3mdev_fib_table_rcu(dev) ? : RT_TABLE_MAIN;
struct fib6_table *tb;
+ if (params->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;
diff --git a/tools/include/uapi/linux/bpf.h b/tools/include/uapi/linux/bpf.h
index 1bb11a6ee6676..2096fbb328a9b 100644
--- a/tools/include/uapi/linux/bpf.h
+++ b/tools/include/uapi/linux/bpf.h
@@ -3167,6 +3167,8 @@ union bpf_attr {
* **BPF_FIB_LOOKUP_DIRECT**
* Do a direct table lookup vs full lookup using FIB
* rules.
+ * If *params*->tbid is non-zero, this value designates
+ * a routing table ID to perform the lookup against.
* **BPF_FIB_LOOKUP_OUTPUT**
* Perform lookup from an egress perspective (default is
* ingress).
@@ -6881,9 +6883,18 @@ 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` flag, a
+ * specific routing table to use for the fib lookup.
+ */
+ __u32 tbid;
+ };
+
__u8 smac[6]; /* ETH_ALEN */
__u8 dmac[6]; /* ETH_ALEN */
};
