Merge "Move BPF offload program from netd to mainline"

    updatable: true,

    min_sdk_version: "current",

    java_libs: ["framework-tethering"],

    bpfs: ["offload.o"],

    apps: ["Tethering"],

    manifest: "manifest.json",

    key: "com.android.tethering.key",

//

// 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

    ],

}

/*

 * 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");