From 1810ef6cdbc6686f458a116ea02d5dc72bc1d1c7 Mon Sep 17 00:00:00 2001 From: Avinash Duduskar Date: Mon, 13 Jul 2026 21:53:04 +0530 Subject: [PATCH] bpf: Add BPF_FIB_LOOKUP_VLAN_INPUT flag to bpf_fib_lookup() helper MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit BPF_FIB_LOOKUP_VLAN resolves a VLAN egress. The reverse is also useful: an XDP program receiving a VLAN-tagged frame on a physical device wants the lookup to behave as if the packet had arrived on the corresponding VLAN subinterface, so iif-based policy routing and VRF table selection use the right ingress. Add BPF_FIB_LOOKUP_VLAN_INPUT. When set, params->h_vlan_proto and params->h_vlan_TCI are read as an input VLAN tag and the matching VLAN device of params->ifindex is resolved with __vlan_find_dev_deep_rcu(). The device must be up and in the same network namespace as params->ifindex (a VLAN device can be moved to another netns while registered on its parent; receive would deliver into that other namespace, which a lookup here cannot represent). If params->ifindex is itself a VLAN device, its inner (QinQ) subinterface is matched. For a bond or team, a tag on a port matches no device and returns NOT_FWDED; pass the master's ifindex. The lookup then runs with the resolved device as the ingress; params->ifindex itself is not modified on the input side. When the resolved device is enslaved to a VRF, both the full lookup (via the l3mdev rule) and BPF_FIB_LOOKUP_DIRECT (via l3mdev_fib_table_rcu()) select the VRF's table from the resolved ingress. That follows from feeding the resolved device to the flow as the ingress (fl4.flowi4_iif = dev->ifindex), which is what makes l3mdev resolve the VRF master from the subinterface rather than from params->ifindex. The two failure classes get different treatment on purpose. A h_vlan_proto other than 802.1Q/802.1ad is API misuse and returns -EINVAL, since it would otherwise reach the WARN in vlan_proto_idx() with a program-controlled value. An unmatched VID, a device that is down, or one in another namespace is a data outcome and returns BPF_FIB_LKUP_RET_NOT_FWDED, matching the DIRECT path when fib_get_table() finds no table and mirroring real ingress, where the receive path drops such frames. A VID of 0 (a priority tag) is looked up literally and normally fails the same way; receive instead processes such frames untagged, so callers should not set the flag for priority tags. Proceeding on the physical device for any of these would be fail-open for the policy-routing cases above. The h_vlan fields share a union with tbid, so the flag cannot be combined with BPF_FIB_LOOKUP_TBID. It describes ingress, so it also cannot be combined with BPF_FIB_LOOKUP_OUTPUT. Both combinations return -EINVAL; restricting now keeps a later relaxation backward compatible. Combining with BPF_FIB_LOOKUP_VLAN is allowed: the tag is consumed on the ingress side and the egress tag is written on success. Under !CONFIG_VLAN_8021Q the __vlan_find_dev_deep_rcu() stub returns NULL, so every lookup with a valid proto returns NOT_FWDED, which is correct since no VLAN device can exist. Suggested-by: Toke Høiland-Jørgensen Signed-off-by: Avinash Duduskar Reviewed-by: Toke Høiland-Jørgensen Reviewed-by: Emil Tsalapatis Link: https://lore.kernel.org/bpf/20260713162305.1237211-3-avinash.duduskar@gmail.com Signed-off-by: Kumar Kartikeya Dwivedi --- include/uapi/linux/bpf.h | 21 ++++++++++++++++++++- 1 file changed, 20 insertions(+), 1 deletion(-) diff --git a/include/uapi/linux/bpf.h b/include/uapi/linux/bpf.h index 54f23c3..2b53f3a 100644 --- a/include/uapi/linux/bpf.h +++ b/include/uapi/linux/bpf.h @@ -3557,6 +3557,22 @@ union bpf_attr { * This flag is only valid for XDP programs; tc programs * receive -EINVAL since they can redirect to the VLAN * device directly. + * **BPF_FIB_LOOKUP_VLAN_INPUT** + * Treat *params*->h_vlan_proto and *params*->h_vlan_TCI + * as an input VLAN tag and run the lookup as if ingress + * had happened on the VLAN subinterface carrying that tag + * on *params*->ifindex. The VID is the low 12 bits of + * *params*->h_vlan_TCI; *params*->h_vlan_proto must be + * ETH_P_8021Q or ETH_P_8021AD in network byte order, else + * **-EINVAL**. If *params*->ifindex is itself a VLAN + * device, its inner (QinQ) subinterface is matched; for a + * bond or team, pass the master's ifindex. An unmatched + * tag, a down device, or one in another namespace returns + * **BPF_FIB_LKUP_RET_NOT_FWDED**, mirroring real ingress. + * A VID of 0 is looked up literally, so do not set this + * flag for priority-tagged frames. Cannot be combined with + * **BPF_FIB_LOOKUP_TBID** or **BPF_FIB_LOOKUP_OUTPUT** + * (returns **-EINVAL**). * * *ctx* is either **struct xdp_md** for XDP programs or * **struct sk_buff** tc cls_act programs. @@ -7365,6 +7381,7 @@ enum { BPF_FIB_LOOKUP_SRC = (1U << 4), BPF_FIB_LOOKUP_MARK = (1U << 5), BPF_FIB_LOOKUP_VLAN = (1U << 6), + BPF_FIB_LOOKUP_VLAN_INPUT = (1U << 7), }; enum { @@ -7435,7 +7452,9 @@ struct bpf_fib_lookup { /* * output with BPF_FIB_LOOKUP_VLAN: set from the * resolved egress VLAN device (see the flag); zeroed - * on other successful lookups. + * on other successful lookups. input with + * BPF_FIB_LOOKUP_VLAN_INPUT: the VLAN tag to scope + * the lookup by. */ __be16 h_vlan_proto; __be16 h_vlan_TCI;