[PATCH bpf-next v6 2/3] bpf: Add BPF_FIB_LOOKUP_VLAN_INPUT flag to bpf_fib_lookup() helper
From: Avinash Duduskar <hidden>
Date: 2026-07-04 09:22:29
Also in:
bpf, linux-kselftest, lkml
Subsystem:
bpf [general] (safe dynamic programs and tools), bpf [networking] (tcx & tc bpf, sock_addr), networking [general], the rest · Maintainers:
Alexei Starovoitov, Daniel Borkmann, Andrii Nakryiko, Eduard Zingerman, Kumar Kartikeya Dwivedi, "David S. Miller", Eric Dumazet, Jakub Kicinski, Paolo Abeni, Linus Torvalds
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 the flag returns NOT_FWDED, which is correct since no VLAN device can exist. Suggested-by: Toke Høiland-Jørgensen <redacted> Reviewed-by: Toke Høiland-Jørgensen <redacted> Signed-off-by: Avinash Duduskar <redacted> --- include/uapi/linux/bpf.h | 21 ++++++++++- net/core/filter.c | 66 +++++++++++++++++++++++++++++++--- tools/include/uapi/linux/bpf.h | 21 ++++++++++- 3 files changed, 101 insertions(+), 7 deletions(-)
diff --git a/include/uapi/linux/bpf.h b/include/uapi/linux/bpf.h
index e00f0392e728..d4218954c50f 100644
--- a/include/uapi/linux/bpf.h
+++ b/include/uapi/linux/bpf.h@@ -3555,6 +3555,22 @@ 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.
@@ -7351,6 +7367,7 @@ 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 {
@@ -7421,7 +7438,9 @@ 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;
diff --git a/net/core/filter.c b/net/core/filter.c
index b5a45485a54b..0ea362fa4287 100644
--- a/net/core/filter.c
+++ b/net/core/filter.c@@ -6229,6 +6229,25 @@ static int bpf_fib_set_fwd_params(struct net_device *dev, return 0; } + +static struct net_device *bpf_fib_vlan_input_dev(struct net_device *dev, + const struct bpf_fib_lookup *params) +{ + __be16 proto = params->h_vlan_proto; + struct net_device *vlan_dev; + u16 vid; + + if (proto != htons(ETH_P_8021Q) && proto != htons(ETH_P_8021AD)) + return ERR_PTR(-EINVAL); + + vid = ntohs(params->h_vlan_TCI) & VLAN_VID_MASK; + vlan_dev = __vlan_find_dev_deep_rcu(dev, proto, vid); + if (!vlan_dev || !(vlan_dev->flags & IFF_UP) || + !net_eq(dev_net(vlan_dev), dev_net(dev))) + return NULL; + + return vlan_dev; +} #endif #if IS_ENABLED(CONFIG_INET)
@@ -6249,6 +6268,14 @@ static int bpf_ipv4_fib_lookup(struct net *net, struct bpf_fib_lookup *params, if (unlikely(!dev)) return -ENODEV; + if (flags & BPF_FIB_LOOKUP_VLAN_INPUT) { + dev = bpf_fib_vlan_input_dev(dev, params); + if (IS_ERR(dev)) + return PTR_ERR(dev); + if (!dev) + return BPF_FIB_LKUP_RET_NOT_FWDED; + } + /* verify forwarding is enabled on this interface */ in_dev = __in_dev_get_rcu(dev); if (unlikely(!in_dev || !IN_DEV_FORWARD(in_dev)))
@@ -6258,7 +6285,11 @@ static int bpf_ipv4_fib_lookup(struct net *net, struct bpf_fib_lookup *params, fl4.flowi4_iif = 1; fl4.flowi4_oif = params->ifindex; } else { - fl4.flowi4_iif = params->ifindex; + /* + * dev->ifindex, not params->ifindex: VLAN_INPUT may have + * resolved dev to a subinterface above. + */ + fl4.flowi4_iif = dev->ifindex; fl4.flowi4_oif = 0; } fl4.flowi4_dscp = inet_dsfield_to_dscp(params->tos);
@@ -6395,6 +6426,14 @@ static int bpf_ipv6_fib_lookup(struct net *net, struct bpf_fib_lookup *params, if (unlikely(!dev)) return -ENODEV; + if (flags & BPF_FIB_LOOKUP_VLAN_INPUT) { + dev = bpf_fib_vlan_input_dev(dev, params); + if (IS_ERR(dev)) + return PTR_ERR(dev); + if (!dev) + return BPF_FIB_LKUP_RET_NOT_FWDED; + } + idev = __in6_dev_get_safely(dev); if (unlikely(!idev || !READ_ONCE(idev->cnf.forwarding))) return BPF_FIB_LKUP_RET_FWD_DISABLED;
@@ -6403,7 +6442,12 @@ static int bpf_ipv6_fib_lookup(struct net *net, struct bpf_fib_lookup *params, fl6.flowi6_iif = 1; oif = fl6.flowi6_oif = params->ifindex; } else { - oif = fl6.flowi6_iif = params->ifindex; + /* + * dev->ifindex, not params->ifindex: VLAN_INPUT may have + * resolved dev to a subinterface above. + */ + oif = dev->ifindex; + fl6.flowi6_iif = oif; fl6.flowi6_oif = 0; strict = RT6_LOOKUP_F_HAS_SADDR; }
@@ -6514,7 +6558,19 @@ static int bpf_ipv6_fib_lookup(struct net *net, struct bpf_fib_lookup *params, #define BPF_FIB_LOOKUP_MASK (BPF_FIB_LOOKUP_DIRECT | BPF_FIB_LOOKUP_OUTPUT | \ BPF_FIB_LOOKUP_SKIP_NEIGH | BPF_FIB_LOOKUP_TBID | \ BPF_FIB_LOOKUP_SRC | BPF_FIB_LOOKUP_MARK | \ - BPF_FIB_LOOKUP_VLAN) + BPF_FIB_LOOKUP_VLAN | BPF_FIB_LOOKUP_VLAN_INPUT) + +static bool bpf_fib_lookup_flags_ok(u32 flags) +{ + if (flags & ~BPF_FIB_LOOKUP_MASK) + return false; + + if ((flags & BPF_FIB_LOOKUP_VLAN_INPUT) && + (flags & (BPF_FIB_LOOKUP_TBID | BPF_FIB_LOOKUP_OUTPUT))) + return false; + + return true; +} BPF_CALL_4(bpf_xdp_fib_lookup, struct xdp_buff *, ctx, struct bpf_fib_lookup *, params, int, plen, u32, flags)
@@ -6522,7 +6578,7 @@ BPF_CALL_4(bpf_xdp_fib_lookup, struct xdp_buff *, ctx, if (plen < sizeof(*params)) return -EINVAL; - if (flags & ~BPF_FIB_LOOKUP_MASK) + if (!bpf_fib_lookup_flags_ok(flags)) return -EINVAL; switch (params->family) {
@@ -6560,7 +6616,7 @@ BPF_CALL_4(bpf_skb_fib_lookup, struct sk_buff *, skb, if (plen < sizeof(*params)) return -EINVAL; - if (flags & ~BPF_FIB_LOOKUP_MASK) + if (!bpf_fib_lookup_flags_ok(flags)) return -EINVAL; if (flags & BPF_FIB_LOOKUP_VLAN)
diff --git a/tools/include/uapi/linux/bpf.h b/tools/include/uapi/linux/bpf.h
index e00f0392e728..d4218954c50f 100644
--- a/tools/include/uapi/linux/bpf.h
+++ b/tools/include/uapi/linux/bpf.h@@ -3555,6 +3555,22 @@ 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.
@@ -7351,6 +7367,7 @@ 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 {
@@ -7421,7 +7438,9 @@ 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;
--
2.54.0