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Mon, 22 Jun 2026 19:52:08 -0700 (PDT) From: Avinash Duduskar To: ast@kernel.org, daniel@iogearbox.net, andrii@kernel.org Cc: eddyz87@gmail.com, memxor@gmail.com, martin.lau@linux.dev, song@kernel.org, yonghong.song@linux.dev, jolsa@kernel.org, emil@etsalapatis.com, john.fastabend@gmail.com, sdf@fomichev.me, davem@davemloft.net, edumazet@google.com, kuba@kernel.org, pabeni@redhat.com, horms@kernel.org, shuah@kernel.org, hawk@kernel.org, yatsenko@meta.com, leon.hwang@linux.dev, kpsingh@kernel.org, a.s.protopopov@gmail.com, ameryhung@gmail.com, rongtao@cestc.cn, eyal.birger@gmail.com, bpf@vger.kernel.org, netdev@vger.kernel.org, linux-kernel@vger.kernel.org, linux-kselftest@vger.kernel.org, toke@redhat.com, dsahern@kernel.org Subject: [PATCH bpf-next v4 1/3] bpf: Add BPF_FIB_LOOKUP_VLAN flag to bpf_fib_lookup() helper Date: Tue, 23 Jun 2026 08:21:45 +0530 Message-ID: <20260623025147.1001664-2-avinash.duduskar@gmail.com> X-Mailer: git-send-email 2.54.0 In-Reply-To: <20260623025147.1001664-1-avinash.duduskar@gmail.com> References: <20260623025147.1001664-1-avinash.duduskar@gmail.com> Precedence: bulk X-Mailing-List: netdev@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit bpf_fib_lookup() returns the FIB-resolved egress ifindex straight from the fib result. When the egress is a VLAN device, the returned ifindex is the VLAN netdev's, which has no XDP xmit handler; XDP programs that want to forward the frame (e.g. xdp-forward) must instead target the underlying physical device and push the VLAN tag themselves. Today the program has no way to learn either the underlying ifindex or the VLAN tag without maintaining its own VLAN-to-ifindex map in userspace and refreshing it on netlink events. Add BPF_FIB_LOOKUP_VLAN. When the caller sets this flag and the fib result is a VLAN device whose immediate parent is a real (non-VLAN) device in the same network namespace, populate the existing output fields params->h_vlan_proto and params->h_vlan_TCI from the VLAN device and replace params->ifindex with the parent's ifindex. params->h_vlan_TCI carries the VID only, with PCP and DEI bits zero; a consumer wanting to set egress priority writes PCP itself. params->smac is the VLAN device's own address, which can differ from the parent's. Only the immediate parent is resolved, via vlan_dev_priv(dev)->real_dev and not vlan_dev_real_dev(), which walks to the bottom of a stack. When the immediate parent is not a real device in the same namespace, the lookup returns BPF_FIB_LKUP_RET_VLAN_FAILURE and leaves params->ifindex at the input. This covers a stacked VLAN (QinQ), where the immediate parent is itself a VLAN device and one h_vlan_proto/h_vlan_TCI pair cannot describe two tags, and a parent in another network namespace (a VLAN device can be moved while its parent stays), whose ifindex would be meaningless in the caller's namespace. A program that wants the VLAN device's own ifindex re-issues the lookup without BPF_FIB_LOOKUP_VLAN, so the unreducible case stays distinct from a physical egress. That distinction matters for XDP: a program cannot xmit on a VLAN device, so a success carrying the VLAN ifindex would make it redirect to a device with no ndo_xdp_xmit and drop the frame at xdp_do_flush(). The swap and the vlan fields are written only on the reduce path; other output fields keep their existing behaviour, so a frag-needed result still reports the route mtu in params->mtu_result. On the skb path without tot_len the deferred mtu check is done against the resolved egress device. To keep that the VLAN device rather than the parent after the swap, bpf_ipv4_fib_lookup()/bpf_ipv6_fib_lookup() hand the FIB-result device back to the caller; the XDP path always runs the route-mtu check and passes NULL. When the flag is not set, behaviour is unchanged: h_vlan_proto and h_vlan_TCI are zeroed and ifindex is left at the FIB result. The new block is compiled only under CONFIG_VLAN_8021Q since vlan_dev_priv() is not defined otherwise; without that config is_vlan_dev() is constant false and the flag is accepted but never acts. That is safe because no VLAN device can exist there, so every egress is already physical. This lets an XDP redirect target the physical device and learn the tag to push in a single lookup, which xdp-forward's optional VLAN mode (xdp-project/xdp-tools#504) wants from the kernel side. The helper's input semantics are unchanged; the reverse direction (supplying a tag as lookup input) is added in the following patch. Suggested-by: Toke Høiland-Jørgensen Signed-off-by: Avinash Duduskar --- include/uapi/linux/bpf.h | 28 +++++++++++++- net/core/filter.c | 69 ++++++++++++++++++++++++---------- tools/include/uapi/linux/bpf.h | 28 +++++++++++++- 3 files changed, 104 insertions(+), 21 deletions(-) diff --git a/include/uapi/linux/bpf.h b/include/uapi/linux/bpf.h index 89b36de5fdbb..8d0058d88eb2 100644 --- a/include/uapi/linux/bpf.h +++ b/include/uapi/linux/bpf.h @@ -3532,6 +3532,26 @@ union bpf_attr { * Use the mark present in *params*->mark for the fib lookup. * This option should not be used with BPF_FIB_LOOKUP_DIRECT, * as it only has meaning for full lookups. + * **BPF_FIB_LOOKUP_VLAN** + * If the fib lookup resolves to a VLAN device whose + * parent is a real (non-VLAN) device, set + * *params*->h_vlan_proto and *params*->h_vlan_TCI from + * the VLAN device and replace *params*->ifindex with the + * parent's ifindex. *params*->h_vlan_TCI carries the VID + * only, with PCP and DEI bits zero; a consumer wanting to + * set egress priority writes PCP itself. *params*->smac is + * the VLAN device's own address, which can differ from the + * parent's. Only the immediate parent is resolved; if it + * is itself a VLAN device (QinQ) or in another namespace, + * the egress cannot be reduced to a physical device plus + * one tag and the lookup returns + * **BPF_FIB_LKUP_RET_VLAN_FAILURE** with *params*->ifindex + * left at the input. Re-issue without + * **BPF_FIB_LOOKUP_VLAN** to obtain the VLAN device's own + * ifindex. The swap and the vlan fields + * are written only on success; other output fields keep + * the helper's existing behaviour, so a frag-needed result + * still reports the route mtu in *params*->mtu_result. * * *ctx* is either **struct xdp_md** for XDP programs or * **struct sk_buff** tc cls_act programs. @@ -7327,6 +7347,7 @@ enum { BPF_FIB_LOOKUP_TBID = (1U << 3), BPF_FIB_LOOKUP_SRC = (1U << 4), BPF_FIB_LOOKUP_MARK = (1U << 5), + BPF_FIB_LOOKUP_VLAN = (1U << 6), }; enum { @@ -7340,6 +7361,7 @@ enum { BPF_FIB_LKUP_RET_NO_NEIGH, /* no neighbor entry for nh */ BPF_FIB_LKUP_RET_FRAG_NEEDED, /* fragmentation required to fwd */ BPF_FIB_LKUP_RET_NO_SRC_ADDR, /* failed to derive IP src addr */ + BPF_FIB_LKUP_RET_VLAN_FAILURE, /* VLAN egress, parent unresolvable */ }; struct bpf_fib_lookup { @@ -7393,7 +7415,11 @@ struct bpf_fib_lookup { union { struct { - /* output */ + /* + * output with BPF_FIB_LOOKUP_VLAN: set from the + * resolved egress VLAN device (see the flag); zeroed + * on other successful lookups. + */ __be16 h_vlan_proto; __be16 h_vlan_TCI; }; diff --git a/net/core/filter.c b/net/core/filter.c index 2e96b4b847ce..8345295d84de 100644 --- a/net/core/filter.c +++ b/net/core/filter.c @@ -6201,10 +6201,28 @@ static const struct bpf_func_proto bpf_skb_get_xfrm_state_proto = { #endif #if IS_ENABLED(CONFIG_INET) || IS_ENABLED(CONFIG_IPV6) -static int bpf_fib_set_fwd_params(struct bpf_fib_lookup *params, u32 mtu) +static int bpf_fib_set_fwd_params(struct net_device *dev, + struct bpf_fib_lookup *params, + u32 flags, u32 mtu) { params->h_vlan_TCI = 0; params->h_vlan_proto = 0; + +#if IS_ENABLED(CONFIG_VLAN_8021Q) + if ((flags & BPF_FIB_LOOKUP_VLAN) && is_vlan_dev(dev)) { + struct net_device *real_dev = vlan_dev_priv(dev)->real_dev; + + if (!is_vlan_dev(real_dev) && + net_eq(dev_net(real_dev), dev_net(dev))) { + params->h_vlan_proto = vlan_dev_vlan_proto(dev); + params->h_vlan_TCI = htons(vlan_dev_vlan_id(dev)); + params->ifindex = real_dev->ifindex; + } else { + return BPF_FIB_LKUP_RET_VLAN_FAILURE; + } + } +#endif + if (mtu) params->mtu_result = mtu; /* union with tot_len */ @@ -6214,8 +6232,10 @@ static int bpf_fib_set_fwd_params(struct bpf_fib_lookup *params, u32 mtu) #if IS_ENABLED(CONFIG_INET) static int bpf_ipv4_fib_lookup(struct net *net, struct bpf_fib_lookup *params, - u32 flags, bool check_mtu) + u32 flags, bool check_mtu, + struct net_device **fwd_dev) { + u32 in_ifindex = params->ifindex; struct neighbour *neigh = NULL; struct fib_nh_common *nhc; struct in_device *in_dev; @@ -6347,16 +6367,23 @@ static int bpf_ipv4_fib_lookup(struct net *net, struct bpf_fib_lookup *params, memcpy(params->smac, dev->dev_addr, ETH_ALEN); set_fwd_params: - return bpf_fib_set_fwd_params(params, mtu); + if (fwd_dev) + *fwd_dev = dev; + err = bpf_fib_set_fwd_params(dev, params, flags, mtu); + if (err == BPF_FIB_LKUP_RET_VLAN_FAILURE) + params->ifindex = in_ifindex; + return err; } #endif #if IS_ENABLED(CONFIG_IPV6) static int bpf_ipv6_fib_lookup(struct net *net, struct bpf_fib_lookup *params, - u32 flags, bool check_mtu) + u32 flags, bool check_mtu, + struct net_device **fwd_dev) { struct in6_addr *src = (struct in6_addr *) params->ipv6_src; struct in6_addr *dst = (struct in6_addr *) params->ipv6_dst; + u32 in_ifindex = params->ifindex; struct fib6_result res = {}; struct neighbour *neigh; struct net_device *dev; @@ -6486,13 +6513,19 @@ static int bpf_ipv6_fib_lookup(struct net *net, struct bpf_fib_lookup *params, memcpy(params->smac, dev->dev_addr, ETH_ALEN); set_fwd_params: - return bpf_fib_set_fwd_params(params, mtu); + if (fwd_dev) + *fwd_dev = dev; + err = bpf_fib_set_fwd_params(dev, params, flags, mtu); + if (err == BPF_FIB_LKUP_RET_VLAN_FAILURE) + params->ifindex = in_ifindex; + return err; } #endif #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_SRC | BPF_FIB_LOOKUP_MARK | \ + BPF_FIB_LOOKUP_VLAN) BPF_CALL_4(bpf_xdp_fib_lookup, struct xdp_buff *, ctx, struct bpf_fib_lookup *, params, int, plen, u32, flags) @@ -6507,12 +6540,12 @@ BPF_CALL_4(bpf_xdp_fib_lookup, struct xdp_buff *, ctx, #if IS_ENABLED(CONFIG_INET) case AF_INET: return bpf_ipv4_fib_lookup(dev_net(ctx->rxq->dev), params, - flags, true); + flags, true, NULL); #endif #if IS_ENABLED(CONFIG_IPV6) case AF_INET6: return bpf_ipv6_fib_lookup(dev_net(ctx->rxq->dev), params, - flags, true); + flags, true, NULL); #endif } return -EAFNOSUPPORT; @@ -6532,6 +6565,7 @@ BPF_CALL_4(bpf_skb_fib_lookup, struct sk_buff *, skb, struct bpf_fib_lookup *, params, int, plen, u32, flags) { struct net *net = dev_net(skb->dev); + struct net_device *fwd_dev = NULL; int rc = -EAFNOSUPPORT; bool check_mtu = false; @@ -6547,29 +6581,26 @@ BPF_CALL_4(bpf_skb_fib_lookup, struct sk_buff *, skb, switch (params->family) { #if IS_ENABLED(CONFIG_INET) case AF_INET: - rc = bpf_ipv4_fib_lookup(net, params, flags, check_mtu); + rc = bpf_ipv4_fib_lookup(net, params, flags, check_mtu, + &fwd_dev); break; #endif #if IS_ENABLED(CONFIG_IPV6) case AF_INET6: - rc = bpf_ipv6_fib_lookup(net, params, flags, check_mtu); + rc = bpf_ipv6_fib_lookup(net, params, flags, check_mtu, + &fwd_dev); break; #endif } if (rc == BPF_FIB_LKUP_RET_SUCCESS && !check_mtu) { - struct net_device *dev; - - /* When tot_len isn't provided by user, check skb - * against MTU of FIB lookup resulting net_device + /* without tot_len, check the skb against the FIB-result + * device's MTU */ - dev = dev_get_by_index_rcu(net, params->ifindex); - if (unlikely(!dev)) - return -ENODEV; - if (!is_skb_forwardable(dev, skb)) + if (!is_skb_forwardable(fwd_dev, skb)) rc = BPF_FIB_LKUP_RET_FRAG_NEEDED; - params->mtu_result = dev->mtu; /* union with tot_len */ + params->mtu_result = fwd_dev->mtu; /* union with tot_len */ } return rc; diff --git a/tools/include/uapi/linux/bpf.h b/tools/include/uapi/linux/bpf.h index 89b36de5fdbb..8d0058d88eb2 100644 --- a/tools/include/uapi/linux/bpf.h +++ b/tools/include/uapi/linux/bpf.h @@ -3532,6 +3532,26 @@ union bpf_attr { * Use the mark present in *params*->mark for the fib lookup. * This option should not be used with BPF_FIB_LOOKUP_DIRECT, * as it only has meaning for full lookups. + * **BPF_FIB_LOOKUP_VLAN** + * If the fib lookup resolves to a VLAN device whose + * parent is a real (non-VLAN) device, set + * *params*->h_vlan_proto and *params*->h_vlan_TCI from + * the VLAN device and replace *params*->ifindex with the + * parent's ifindex. *params*->h_vlan_TCI carries the VID + * only, with PCP and DEI bits zero; a consumer wanting to + * set egress priority writes PCP itself. *params*->smac is + * the VLAN device's own address, which can differ from the + * parent's. Only the immediate parent is resolved; if it + * is itself a VLAN device (QinQ) or in another namespace, + * the egress cannot be reduced to a physical device plus + * one tag and the lookup returns + * **BPF_FIB_LKUP_RET_VLAN_FAILURE** with *params*->ifindex + * left at the input. Re-issue without + * **BPF_FIB_LOOKUP_VLAN** to obtain the VLAN device's own + * ifindex. The swap and the vlan fields + * are written only on success; other output fields keep + * the helper's existing behaviour, so a frag-needed result + * still reports the route mtu in *params*->mtu_result. * * *ctx* is either **struct xdp_md** for XDP programs or * **struct sk_buff** tc cls_act programs. @@ -7327,6 +7347,7 @@ enum { BPF_FIB_LOOKUP_TBID = (1U << 3), BPF_FIB_LOOKUP_SRC = (1U << 4), BPF_FIB_LOOKUP_MARK = (1U << 5), + BPF_FIB_LOOKUP_VLAN = (1U << 6), }; enum { @@ -7340,6 +7361,7 @@ enum { BPF_FIB_LKUP_RET_NO_NEIGH, /* no neighbor entry for nh */ BPF_FIB_LKUP_RET_FRAG_NEEDED, /* fragmentation required to fwd */ BPF_FIB_LKUP_RET_NO_SRC_ADDR, /* failed to derive IP src addr */ + BPF_FIB_LKUP_RET_VLAN_FAILURE, /* VLAN egress, parent unresolvable */ }; struct bpf_fib_lookup { @@ -7393,7 +7415,11 @@ struct bpf_fib_lookup { union { struct { - /* output */ + /* + * output with BPF_FIB_LOOKUP_VLAN: set from the + * resolved egress VLAN device (see the flag); zeroed + * on other successful lookups. + */ __be16 h_vlan_proto; __be16 h_vlan_TCI; }; -- 2.54.0