/* * 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 #include #include #include #include #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");