diff --git a/Tethering/bpf_progs/Android.bp b/Tethering/bpf_progs/Android.bp
new file mode 100644
index 0000000..d54f861
--- /dev/null
+++ b/Tethering/bpf_progs/Android.bp
@@ -0,0 +1,33 @@
+//
+// Copyright (C) 2020 The Android Open Source Project
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//      http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+//
+
+//
+// bpf kernel programs
+//
+bpf {
+    name: "offload.o",
+    srcs: ["offload.c"],
+    cflags: [
+        "-Wall",
+        "-Werror",
+    ],
+    include_dirs: [
+        // TODO: get rid of system/netd.
+        "system/netd/bpf_progs",             // for bpf_net_helpers.h
+        "system/netd/libnetdbpf/include",    // for bpf_shared.h
+        "system/netd/libnetdutils/include",  // for UidConstants.h
+    ],
+}
diff --git a/Tethering/bpf_progs/offload.c b/Tethering/bpf_progs/offload.c
new file mode 100644
index 0000000..cc5af31
--- /dev/null
+++ b/Tethering/bpf_progs/offload.c
@@ -0,0 +1,207 @@
+/*
+ * Copyright (C) 2020 The Android Open Source Project
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+#include <linux/if.h>
+#include <linux/ip.h>
+#include <linux/ipv6.h>
+#include <linux/pkt_cls.h>
+#include <linux/tcp.h>
+
+#include "bpf_helpers.h"
+#include "bpf_net_helpers.h"
+#include "netdbpf/bpf_shared.h"
+
+DEFINE_BPF_MAP_GRW(tether_ingress_map, HASH, TetherIngressKey, TetherIngressValue, 64,
+                   AID_NETWORK_STACK)
+
+// Tethering stats, indexed by upstream interface.
+DEFINE_BPF_MAP_GRW(tether_stats_map, HASH, uint32_t, TetherStatsValue, 16, AID_NETWORK_STACK)
+
+// Tethering data limit, indexed by upstream interface.
+// (tethering allowed when stats[iif].rxBytes + stats[iif].txBytes < limit[iif])
+DEFINE_BPF_MAP_GRW(tether_limit_map, HASH, uint32_t, uint64_t, 16, AID_NETWORK_STACK)
+
+static inline __always_inline int do_forward(struct __sk_buff* skb, bool is_ethernet) {
+    int l2_header_size = is_ethernet ? sizeof(struct ethhdr) : 0;
+    void* data = (void*)(long)skb->data;
+    const void* data_end = (void*)(long)skb->data_end;
+    struct ethhdr* eth = is_ethernet ? data : NULL;  // used iff is_ethernet
+    struct ipv6hdr* ip6 = is_ethernet ? (void*)(eth + 1) : data;
+
+    // Must be meta-ethernet IPv6 frame
+    if (skb->protocol != htons(ETH_P_IPV6)) return TC_ACT_OK;
+
+    // Must have (ethernet and) ipv6 header
+    if (data + l2_header_size + sizeof(*ip6) > data_end) return TC_ACT_OK;
+
+    // Ethertype - if present - must be IPv6
+    if (is_ethernet && (eth->h_proto != htons(ETH_P_IPV6))) return TC_ACT_OK;
+
+    // IP version must be 6
+    if (ip6->version != 6) return TC_ACT_OK;
+
+    // Cannot decrement during forward if already zero or would be zero,
+    // Let the kernel's stack handle these cases and generate appropriate ICMP errors.
+    if (ip6->hop_limit <= 1) return TC_ACT_OK;
+
+    // Protect against forwarding packets sourced from ::1 or fe80::/64 or other weirdness.
+    __be32 src32 = ip6->saddr.s6_addr32[0];
+    if (src32 != htonl(0x0064ff9b) &&                        // 64:ff9b:/32 incl. XLAT464 WKP
+        (src32 & htonl(0xe0000000)) != htonl(0x20000000))    // 2000::/3 Global Unicast
+        return TC_ACT_OK;
+
+    TetherIngressKey k = {
+            .iif = skb->ifindex,
+            .neigh6 = ip6->daddr,
+    };
+
+    TetherIngressValue* v = bpf_tether_ingress_map_lookup_elem(&k);
+
+    // If we don't find any offload information then simply let the core stack handle it...
+    if (!v) return TC_ACT_OK;
+
+    uint32_t stat_and_limit_k = skb->ifindex;
+
+    TetherStatsValue* stat_v = bpf_tether_stats_map_lookup_elem(&stat_and_limit_k);
+
+    // If we don't have anywhere to put stats, then abort...
+    if (!stat_v) return TC_ACT_OK;
+
+    uint64_t* limit_v = bpf_tether_limit_map_lookup_elem(&stat_and_limit_k);
+
+    // If we don't have a limit, then abort...
+    if (!limit_v) return TC_ACT_OK;
+
+    // Required IPv6 minimum mtu is 1280, below that not clear what we should do, abort...
+    const int pmtu = v->pmtu;
+    if (pmtu < IPV6_MIN_MTU) return TC_ACT_OK;
+
+    // Approximate handling of TCP/IPv6 overhead for incoming LRO/GRO packets: default
+    // outbound path mtu of 1500 is not necessarily correct, but worst case we simply
+    // undercount, which is still better then not accounting for this overhead at all.
+    // Note: this really shouldn't be device/path mtu at all, but rather should be
+    // derived from this particular connection's mss (ie. from gro segment size).
+    // This would require a much newer kernel with newer ebpf accessors.
+    // (This is also blindly assuming 12 bytes of tcp timestamp option in tcp header)
+    uint64_t packets = 1;
+    uint64_t bytes = skb->len;
+    if (bytes > pmtu) {
+        const int tcp_overhead = sizeof(struct ipv6hdr) + sizeof(struct tcphdr) + 12;
+        const int mss = pmtu - tcp_overhead;
+        const uint64_t payload = bytes - tcp_overhead;
+        packets = (payload + mss - 1) / mss;
+        bytes = tcp_overhead * packets + payload;
+    }
+
+    // Are we past the limit?  If so, then abort...
+    // Note: will not overflow since u64 is 936 years even at 5Gbps.
+    // Do not drop here.  Offload is just that, whenever we fail to handle
+    // a packet we let the core stack deal with things.
+    // (The core stack needs to handle limits correctly anyway,
+    // since we don't offload all traffic in both directions)
+    if (stat_v->rxBytes + stat_v->txBytes + bytes > *limit_v) return TC_ACT_OK;
+
+    if (!is_ethernet) {
+        is_ethernet = true;
+        l2_header_size = sizeof(struct ethhdr);
+        // Try to inject an ethernet header, and simply return if we fail
+        if (bpf_skb_change_head(skb, l2_header_size, /*flags*/ 0)) {
+            __sync_fetch_and_add(&stat_v->rxErrors, 1);
+            return TC_ACT_OK;
+        }
+
+        // bpf_skb_change_head() invalidates all pointers - reload them
+        data = (void*)(long)skb->data;
+        data_end = (void*)(long)skb->data_end;
+        eth = data;
+        ip6 = (void*)(eth + 1);
+
+        // I do not believe this can ever happen, but keep the verifier happy...
+        if (data + l2_header_size + sizeof(*ip6) > data_end) {
+            __sync_fetch_and_add(&stat_v->rxErrors, 1);
+            return TC_ACT_SHOT;
+        }
+    };
+
+    // CHECKSUM_COMPLETE is a 16-bit one's complement sum,
+    // thus corrections for it need to be done in 16-byte chunks at even offsets.
+    // IPv6 nexthdr is at offset 6, while hop limit is at offset 7
+    uint8_t old_hl = ip6->hop_limit;
+    --ip6->hop_limit;
+    uint8_t new_hl = ip6->hop_limit;
+
+    // bpf_csum_update() always succeeds if the skb is CHECKSUM_COMPLETE and returns an error
+    // (-ENOTSUPP) if it isn't.
+    bpf_csum_update(skb, 0xFFFF - ntohs(old_hl) + ntohs(new_hl));
+
+    __sync_fetch_and_add(&stat_v->rxPackets, packets);
+    __sync_fetch_and_add(&stat_v->rxBytes, bytes);
+
+    // Overwrite any mac header with the new one
+    *eth = v->macHeader;
+
+    // Redirect to forwarded interface.
+    //
+    // Note that bpf_redirect() cannot fail unless you pass invalid flags.
+    // The redirect actually happens after the ebpf program has already terminated,
+    // and can fail for example for mtu reasons at that point in time, but there's nothing
+    // we can do about it here.
+    return bpf_redirect(v->oif, 0 /* this is effectively BPF_F_EGRESS */);
+}
+
+SEC("schedcls/ingress/tether_ether")
+int sched_cls_ingress_tether_ether(struct __sk_buff* skb) {
+    return do_forward(skb, true);
+}
+
+// Note: section names must be unique to prevent programs from appending to each other,
+// so instead the bpf loader will strip everything past the final $ symbol when actually
+// pinning the program into the filesystem.
+//
+// bpf_skb_change_head() is only present on 4.14+ and 2 trivial kernel patches are needed:
+//   ANDROID: net: bpf: Allow TC programs to call BPF_FUNC_skb_change_head
+//   ANDROID: net: bpf: permit redirect from ingress L3 to egress L2 devices at near max mtu
+// (the first of those has already been upstreamed)
+//
+// 5.4 kernel support was only added to Android Common Kernel in R,
+// and thus a 5.4 kernel always supports this.
+//
+// Hence, this mandatory (must load successfully) implementation for 5.4+ kernels:
+DEFINE_BPF_PROG_KVER("schedcls/ingress/tether_rawip$5_4", AID_ROOT, AID_ROOT,
+                     sched_cls_ingress_tether_rawip_5_4, KVER(5, 4, 0))
+(struct __sk_buff* skb) {
+    return do_forward(skb, false);
+}
+
+// and this identical optional (may fail to load) implementation for [4.14..5.4) patched kernels:
+DEFINE_OPTIONAL_BPF_PROG_KVER_RANGE("schedcls/ingress/tether_rawip$4_14", AID_ROOT, AID_ROOT,
+                                    sched_cls_ingress_tether_rawip_4_14, KVER(4, 14, 0),
+                                    KVER(5, 4, 0))
+(struct __sk_buff* skb) {
+    return do_forward(skb, false);
+}
+
+// and define a no-op stub for [4.9,4.14) and unpatched [4.14,5.4) kernels.
+// (if the above real 4.14+ program loaded successfully, then bpfloader will have already pinned
+// it at the same location this one would be pinned at and will thus skip loading this stub)
+DEFINE_BPF_PROG_KVER_RANGE("schedcls/ingress/tether_rawip$stub", AID_ROOT, AID_ROOT,
+                           sched_cls_ingress_tether_rawip_stub, KVER_NONE, KVER(5, 4, 0))
+(struct __sk_buff* skb) {
+    return TC_ACT_OK;
+}
+
+LICENSE("Apache 2.0");
+CRITICAL("netd");