/* SPDX-License-Identifier: LGPL-2.1+ */ #include #include #include #include #include #include #include #include #include #include #include #include #include #include #include "alloc-util.h" #include "bpf-firewall.h" #include "bpf-program.h" #include "fd-util.h" #include "ip-address-access.h" #include "memory-util.h" #include "missing_syscall.h" #include "unit.h" #include "virt.h" enum { MAP_KEY_PACKETS, MAP_KEY_BYTES, }; enum { ACCESS_ALLOWED = 1, ACCESS_DENIED = 2, }; /* Compile instructions for one list of addresses, one direction and one specific verdict on matches. */ static int add_lookup_instructions( BPFProgram *p, int map_fd, int protocol, bool is_ingress, int verdict) { int r, addr_offset, addr_size; assert(p); assert(map_fd >= 0); switch (protocol) { case ETH_P_IP: addr_size = sizeof(uint32_t); addr_offset = is_ingress ? offsetof(struct iphdr, saddr) : offsetof(struct iphdr, daddr); break; case ETH_P_IPV6: addr_size = 4 * sizeof(uint32_t); addr_offset = is_ingress ? offsetof(struct ip6_hdr, ip6_src.s6_addr) : offsetof(struct ip6_hdr, ip6_dst.s6_addr); break; default: return -EAFNOSUPPORT; } do { /* Compare IPv4 with one word instruction (32bit) */ struct bpf_insn insn[] = { /* If skb->protocol != ETH_P_IP, skip this whole block. The offset will be set later. */ BPF_JMP_IMM(BPF_JNE, BPF_REG_7, htobe16(protocol), 0), /* * Call into BPF_FUNC_skb_load_bytes to load the dst/src IP address * * R1: Pointer to the skb * R2: Data offset * R3: Destination buffer on the stack (r10 - 4) * R4: Number of bytes to read (4) */ BPF_MOV64_REG(BPF_REG_1, BPF_REG_6), BPF_MOV32_IMM(BPF_REG_2, addr_offset), BPF_MOV64_REG(BPF_REG_3, BPF_REG_10), BPF_ALU64_IMM(BPF_ADD, BPF_REG_3, -addr_size), BPF_MOV32_IMM(BPF_REG_4, addr_size), BPF_RAW_INSN(BPF_JMP | BPF_CALL, 0, 0, 0, BPF_FUNC_skb_load_bytes), /* * Call into BPF_FUNC_map_lookup_elem to see if the address matches any entry in the * LPM trie map. For this to work, the prefixlen field of 'struct bpf_lpm_trie_key' * has to be set to the maximum possible value. * * On success, the looked up value is stored in R0. For this application, the actual * value doesn't matter, however; we just set the bit in @verdict in R8 if we found any * matching value. */ BPF_LD_MAP_FD(BPF_REG_1, map_fd), BPF_MOV64_REG(BPF_REG_2, BPF_REG_10), BPF_ALU64_IMM(BPF_ADD, BPF_REG_2, -addr_size - sizeof(uint32_t)), BPF_ST_MEM(BPF_W, BPF_REG_2, 0, addr_size * 8), BPF_RAW_INSN(BPF_JMP | BPF_CALL, 0, 0, 0, BPF_FUNC_map_lookup_elem), BPF_JMP_IMM(BPF_JEQ, BPF_REG_0, 0, 1), BPF_ALU32_IMM(BPF_OR, BPF_REG_8, verdict), }; /* Jump label fixup */ insn[0].off = ELEMENTSOF(insn) - 1; r = bpf_program_add_instructions(p, insn, ELEMENTSOF(insn)); if (r < 0) return r; } while (false); return 0; } static int bpf_firewall_compile_bpf( Unit *u, bool is_ingress, BPFProgram **ret) { struct bpf_insn pre_insn[] = { /* * When the eBPF program is entered, R1 contains the address of the skb. * However, R1-R5 are scratch registers that are not preserved when calling * into kernel functions, so we need to save anything that's supposed to * stay around to R6-R9. Save the skb to R6. */ BPF_MOV64_REG(BPF_REG_6, BPF_REG_1), /* * Although we cannot access the skb data directly from eBPF programs used in this * scenario, the kernel has prepared some fields for us to access through struct __sk_buff. * Load the protocol (IPv4, IPv6) used by the packet in flight once and cache it in R7 * for later use. */ BPF_LDX_MEM(BPF_W, BPF_REG_7, BPF_REG_6, offsetof(struct __sk_buff, protocol)), /* * R8 is used to keep track of whether any address check has explicitly allowed or denied the packet * through ACCESS_DENIED or ACCESS_ALLOWED bits. Reset them both to 0 in the beginning. */ BPF_MOV32_IMM(BPF_REG_8, 0), }; /* * The access checkers compiled for the configured allowance and denial lists * write to R8 at runtime. The following code prepares for an early exit that * skip the accounting if the packet is denied. * * R0 = 1 * if (R8 == ACCESS_DENIED) * R0 = 0 * * This means that if both ACCESS_DENIED and ACCESS_ALLOWED are set, the packet * is allowed to pass. */ struct bpf_insn post_insn[] = { BPF_MOV64_IMM(BPF_REG_0, 1), BPF_JMP_IMM(BPF_JNE, BPF_REG_8, ACCESS_DENIED, 1), BPF_MOV64_IMM(BPF_REG_0, 0), }; _cleanup_(bpf_program_unrefp) BPFProgram *p = NULL; int accounting_map_fd, r; bool access_enabled; assert(u); assert(ret); accounting_map_fd = is_ingress ? u->ip_accounting_ingress_map_fd : u->ip_accounting_egress_map_fd; access_enabled = u->ipv4_allow_map_fd >= 0 || u->ipv6_allow_map_fd >= 0 || u->ipv4_deny_map_fd >= 0 || u->ipv6_deny_map_fd >= 0; if (accounting_map_fd < 0 && !access_enabled) { *ret = NULL; return 0; } r = bpf_program_new(BPF_PROG_TYPE_CGROUP_SKB, &p); if (r < 0) return r; r = bpf_program_add_instructions(p, pre_insn, ELEMENTSOF(pre_insn)); if (r < 0) return r; if (access_enabled) { /* * The simple rule this function translates into eBPF instructions is: * * - Access will be granted when an address matches an entry in @list_allow * - Otherwise, access will be denied when an address matches an entry in @list_deny * - Otherwise, access will be granted */ if (u->ipv4_deny_map_fd >= 0) { r = add_lookup_instructions(p, u->ipv4_deny_map_fd, ETH_P_IP, is_ingress, ACCESS_DENIED); if (r < 0) return r; } if (u->ipv6_deny_map_fd >= 0) { r = add_lookup_instructions(p, u->ipv6_deny_map_fd, ETH_P_IPV6, is_ingress, ACCESS_DENIED); if (r < 0) return r; } if (u->ipv4_allow_map_fd >= 0) { r = add_lookup_instructions(p, u->ipv4_allow_map_fd, ETH_P_IP, is_ingress, ACCESS_ALLOWED); if (r < 0) return r; } if (u->ipv6_allow_map_fd >= 0) { r = add_lookup_instructions(p, u->ipv6_allow_map_fd, ETH_P_IPV6, is_ingress, ACCESS_ALLOWED); if (r < 0) return r; } } r = bpf_program_add_instructions(p, post_insn, ELEMENTSOF(post_insn)); if (r < 0) return r; if (accounting_map_fd >= 0) { struct bpf_insn insn[] = { /* * If R0 == 0, the packet will be denied; skip the accounting instructions in this case. * The jump label will be fixed up later. */ BPF_JMP_IMM(BPF_JEQ, BPF_REG_0, 0, 0), /* Count packets */ BPF_MOV64_IMM(BPF_REG_0, MAP_KEY_PACKETS), /* r0 = 0 */ BPF_STX_MEM(BPF_W, BPF_REG_10, BPF_REG_0, -4), /* *(u32 *)(fp - 4) = r0 */ BPF_MOV64_REG(BPF_REG_2, BPF_REG_10), BPF_ALU64_IMM(BPF_ADD, BPF_REG_2, -4), /* r2 = fp - 4 */ BPF_LD_MAP_FD(BPF_REG_1, accounting_map_fd), /* load map fd to r1 */ BPF_RAW_INSN(BPF_JMP | BPF_CALL, 0, 0, 0, BPF_FUNC_map_lookup_elem), BPF_JMP_IMM(BPF_JEQ, BPF_REG_0, 0, 2), BPF_MOV64_IMM(BPF_REG_1, 1), /* r1 = 1 */ BPF_RAW_INSN(BPF_STX | BPF_XADD | BPF_DW, BPF_REG_0, BPF_REG_1, 0, 0), /* xadd r0 += r1 */ /* Count bytes */ BPF_MOV64_IMM(BPF_REG_0, MAP_KEY_BYTES), /* r0 = 1 */ BPF_STX_MEM(BPF_W, BPF_REG_10, BPF_REG_0, -4), /* *(u32 *)(fp - 4) = r0 */ BPF_MOV64_REG(BPF_REG_2, BPF_REG_10), BPF_ALU64_IMM(BPF_ADD, BPF_REG_2, -4), /* r2 = fp - 4 */ BPF_LD_MAP_FD(BPF_REG_1, accounting_map_fd), BPF_RAW_INSN(BPF_JMP | BPF_CALL, 0, 0, 0, BPF_FUNC_map_lookup_elem), BPF_JMP_IMM(BPF_JEQ, BPF_REG_0, 0, 2), BPF_LDX_MEM(BPF_W, BPF_REG_1, BPF_REG_6, offsetof(struct __sk_buff, len)), /* r1 = skb->len */ BPF_RAW_INSN(BPF_STX | BPF_XADD | BPF_DW, BPF_REG_0, BPF_REG_1, 0, 0), /* xadd r0 += r1 */ /* Allow the packet to pass */ BPF_MOV64_IMM(BPF_REG_0, 1), }; /* Jump label fixup */ insn[0].off = ELEMENTSOF(insn) - 1; r = bpf_program_add_instructions(p, insn, ELEMENTSOF(insn)); if (r < 0) return r; } do { /* * Exit from the eBPF program, R0 contains the verdict. * 0 means the packet is denied, 1 means the packet may pass. */ struct bpf_insn insn[] = { BPF_EXIT_INSN() }; r = bpf_program_add_instructions(p, insn, ELEMENTSOF(insn)); if (r < 0) return r; } while (false); *ret = TAKE_PTR(p); return 0; } static int bpf_firewall_count_access_items(IPAddressAccessItem *list, size_t *n_ipv4, size_t *n_ipv6) { IPAddressAccessItem *a; assert(n_ipv4); assert(n_ipv6); LIST_FOREACH(items, a, list) { switch (a->family) { case AF_INET: (*n_ipv4)++; break; case AF_INET6: (*n_ipv6)++; break; default: return -EAFNOSUPPORT; } } return 0; } static int bpf_firewall_add_access_items( IPAddressAccessItem *list, int ipv4_map_fd, int ipv6_map_fd, int verdict) { struct bpf_lpm_trie_key *key_ipv4, *key_ipv6; uint64_t value = verdict; IPAddressAccessItem *a; int r; key_ipv4 = alloca0(offsetof(struct bpf_lpm_trie_key, data) + sizeof(uint32_t)); key_ipv6 = alloca0(offsetof(struct bpf_lpm_trie_key, data) + sizeof(uint32_t) * 4); LIST_FOREACH(items, a, list) { switch (a->family) { case AF_INET: key_ipv4->prefixlen = a->prefixlen; memcpy(key_ipv4->data, &a->address, sizeof(uint32_t)); r = bpf_map_update_element(ipv4_map_fd, key_ipv4, &value); if (r < 0) return r; break; case AF_INET6: key_ipv6->prefixlen = a->prefixlen; memcpy(key_ipv6->data, &a->address, 4 * sizeof(uint32_t)); r = bpf_map_update_element(ipv6_map_fd, key_ipv6, &value); if (r < 0) return r; break; default: return -EAFNOSUPPORT; } } return 0; } static int bpf_firewall_prepare_access_maps( Unit *u, int verdict, int *ret_ipv4_map_fd, int *ret_ipv6_map_fd) { _cleanup_close_ int ipv4_map_fd = -1, ipv6_map_fd = -1; size_t n_ipv4 = 0, n_ipv6 = 0; Unit *p; int r; assert(ret_ipv4_map_fd); assert(ret_ipv6_map_fd); for (p = u; p; p = UNIT_DEREF(p->slice)) { CGroupContext *cc; cc = unit_get_cgroup_context(p); if (!cc) continue; bpf_firewall_count_access_items(verdict == ACCESS_ALLOWED ? cc->ip_address_allow : cc->ip_address_deny, &n_ipv4, &n_ipv6); } if (n_ipv4 > 0) { ipv4_map_fd = bpf_map_new( BPF_MAP_TYPE_LPM_TRIE, offsetof(struct bpf_lpm_trie_key, data) + sizeof(uint32_t), sizeof(uint64_t), n_ipv4, BPF_F_NO_PREALLOC); if (ipv4_map_fd < 0) return ipv4_map_fd; } if (n_ipv6 > 0) { ipv6_map_fd = bpf_map_new( BPF_MAP_TYPE_LPM_TRIE, offsetof(struct bpf_lpm_trie_key, data) + sizeof(uint32_t)*4, sizeof(uint64_t), n_ipv6, BPF_F_NO_PREALLOC); if (ipv6_map_fd < 0) return ipv6_map_fd; } for (p = u; p; p = UNIT_DEREF(p->slice)) { CGroupContext *cc; cc = unit_get_cgroup_context(p); if (!cc) continue; r = bpf_firewall_add_access_items(verdict == ACCESS_ALLOWED ? cc->ip_address_allow : cc->ip_address_deny, ipv4_map_fd, ipv6_map_fd, verdict); if (r < 0) return r; } *ret_ipv4_map_fd = ipv4_map_fd; *ret_ipv6_map_fd = ipv6_map_fd; ipv4_map_fd = ipv6_map_fd = -1; return 0; } static int bpf_firewall_prepare_accounting_maps(Unit *u, bool enabled, int *fd_ingress, int *fd_egress) { int r; assert(u); assert(fd_ingress); assert(fd_egress); if (enabled) { if (*fd_ingress < 0) { r = bpf_map_new(BPF_MAP_TYPE_ARRAY, sizeof(int), sizeof(uint64_t), 2, 0); if (r < 0) return r; *fd_ingress = r; } if (*fd_egress < 0) { r = bpf_map_new(BPF_MAP_TYPE_ARRAY, sizeof(int), sizeof(uint64_t), 2, 0); if (r < 0) return r; *fd_egress = r; } } else { *fd_ingress = safe_close(*fd_ingress); *fd_egress = safe_close(*fd_egress); zero(u->ip_accounting_extra); } return 0; } int bpf_firewall_compile(Unit *u) { CGroupContext *cc; int r, supported; assert(u); cc = unit_get_cgroup_context(u); if (!cc) return -EINVAL; supported = bpf_firewall_supported(); if (supported < 0) return supported; if (supported == BPF_FIREWALL_UNSUPPORTED) return log_unit_debug_errno(u, SYNTHETIC_ERRNO(EOPNOTSUPP), "BPF firewalling not supported on this manager, proceeding without."); if (supported != BPF_FIREWALL_SUPPORTED_WITH_MULTI && u->type == UNIT_SLICE) /* If BPF_F_ALLOW_MULTI is not supported we don't support any BPF magic on inner nodes (i.e. on slice * units), since that would mean leaf nodes couldn't do any BPF anymore at all. Under the assumption * that BPF is more interesting on leaf nodes we hence avoid it on inner nodes in that case. This is * consistent with old systemd behaviour from before v238, where BPF wasn't supported in inner nodes at * all, either. */ return log_unit_debug_errno(u, SYNTHETIC_ERRNO(EOPNOTSUPP), "BPF_F_ALLOW_MULTI is not supported on this manager, not doing BPF firewall on slice units."); /* Note that when we compile a new firewall we first flush out the access maps and the BPF programs themselves, * but we reuse the the accounting maps. That way the firewall in effect always maps to the actual * configuration, but we don't flush out the accounting unnecessarily */ u->ip_bpf_ingress = bpf_program_unref(u->ip_bpf_ingress); u->ip_bpf_egress = bpf_program_unref(u->ip_bpf_egress); u->ipv4_allow_map_fd = safe_close(u->ipv4_allow_map_fd); u->ipv4_deny_map_fd = safe_close(u->ipv4_deny_map_fd); u->ipv6_allow_map_fd = safe_close(u->ipv6_allow_map_fd); u->ipv6_deny_map_fd = safe_close(u->ipv6_deny_map_fd); if (u->type != UNIT_SLICE) { /* In inner nodes we only do accounting, we do not actually bother with access control. However, leaf * nodes will incorporate all IP access rules set on all their parent nodes. This has the benefit that * they can optionally cancel out system-wide rules. Since inner nodes can't contain processes this * means that all configure IP access rules *will* take effect on processes, even though we never * compile them for inner nodes. */ r = bpf_firewall_prepare_access_maps(u, ACCESS_ALLOWED, &u->ipv4_allow_map_fd, &u->ipv6_allow_map_fd); if (r < 0) return log_unit_error_errno(u, r, "Preparation of eBPF allow maps failed: %m"); r = bpf_firewall_prepare_access_maps(u, ACCESS_DENIED, &u->ipv4_deny_map_fd, &u->ipv6_deny_map_fd); if (r < 0) return log_unit_error_errno(u, r, "Preparation of eBPF deny maps failed: %m"); } r = bpf_firewall_prepare_accounting_maps(u, cc->ip_accounting, &u->ip_accounting_ingress_map_fd, &u->ip_accounting_egress_map_fd); if (r < 0) return log_unit_error_errno(u, r, "Preparation of eBPF accounting maps failed: %m"); r = bpf_firewall_compile_bpf(u, true, &u->ip_bpf_ingress); if (r < 0) return log_unit_error_errno(u, r, "Compilation for ingress BPF program failed: %m"); r = bpf_firewall_compile_bpf(u, false, &u->ip_bpf_egress); if (r < 0) return log_unit_error_errno(u, r, "Compilation for egress BPF program failed: %m"); return 0; } int bpf_firewall_install(Unit *u) { _cleanup_free_ char *path = NULL; CGroupContext *cc; int r, supported; uint32_t flags; assert(u); cc = unit_get_cgroup_context(u); if (!cc) return -EINVAL; if (!u->cgroup_path) return -EINVAL; if (!u->cgroup_realized) return -EINVAL; supported = bpf_firewall_supported(); if (supported < 0) return supported; if (supported == BPF_FIREWALL_UNSUPPORTED) { log_unit_debug(u, "BPF firewalling not supported on this manager, proceeding without."); return -EOPNOTSUPP; } if (supported != BPF_FIREWALL_SUPPORTED_WITH_MULTI && u->type == UNIT_SLICE) { log_unit_debug(u, "BPF_F_ALLOW_MULTI is not supported on this manager, not doing BPF firewall on slice units."); return -EOPNOTSUPP; } r = cg_get_path(SYSTEMD_CGROUP_CONTROLLER, u->cgroup_path, NULL, &path); if (r < 0) return log_unit_error_errno(u, r, "Failed to determine cgroup path: %m"); flags = (supported == BPF_FIREWALL_SUPPORTED_WITH_MULTI && (u->type == UNIT_SLICE || unit_cgroup_delegate(u))) ? BPF_F_ALLOW_MULTI : 0; /* Unref the old BPF program (which will implicitly detach it) right before attaching the new program, to * minimize the time window when we don't account for IP traffic. */ u->ip_bpf_egress_installed = bpf_program_unref(u->ip_bpf_egress_installed); u->ip_bpf_ingress_installed = bpf_program_unref(u->ip_bpf_ingress_installed); if (u->ip_bpf_egress) { r = bpf_program_cgroup_attach(u->ip_bpf_egress, BPF_CGROUP_INET_EGRESS, path, flags); if (r < 0) return log_unit_error_errno(u, r, "Attaching egress BPF program to cgroup %s failed: %m", path); /* Remember that this BPF program is installed now. */ u->ip_bpf_egress_installed = bpf_program_ref(u->ip_bpf_egress); } if (u->ip_bpf_ingress) { r = bpf_program_cgroup_attach(u->ip_bpf_ingress, BPF_CGROUP_INET_INGRESS, path, flags); if (r < 0) return log_unit_error_errno(u, r, "Attaching ingress BPF program to cgroup %s failed: %m", path); u->ip_bpf_ingress_installed = bpf_program_ref(u->ip_bpf_ingress); } return 0; } int bpf_firewall_read_accounting(int map_fd, uint64_t *ret_bytes, uint64_t *ret_packets) { uint64_t key, packets; int r; if (map_fd < 0) return -EBADF; if (ret_packets) { key = MAP_KEY_PACKETS; r = bpf_map_lookup_element(map_fd, &key, &packets); if (r < 0) return r; } if (ret_bytes) { key = MAP_KEY_BYTES; r = bpf_map_lookup_element(map_fd, &key, ret_bytes); if (r < 0) return r; } if (ret_packets) *ret_packets = packets; return 0; } int bpf_firewall_reset_accounting(int map_fd) { uint64_t key, value = 0; int r; if (map_fd < 0) return -EBADF; key = MAP_KEY_PACKETS; r = bpf_map_update_element(map_fd, &key, &value); if (r < 0) return r; key = MAP_KEY_BYTES; return bpf_map_update_element(map_fd, &key, &value); } static int bpf_firewall_unsupported_reason = 0; int bpf_firewall_supported(void) { struct bpf_insn trivial[] = { BPF_MOV64_IMM(BPF_REG_0, 1), BPF_EXIT_INSN() }; _cleanup_(bpf_program_unrefp) BPFProgram *program = NULL; static int supported = -1; union bpf_attr attr; int fd, r; /* Checks whether BPF firewalling is supported. For this, we check five things: * * a) whether we are privileged * b) whether the unified hierarchy is being used * c) the BPF implementation in the kernel supports BPF LPM TRIE maps, which we require * d) the BPF implementation in the kernel supports BPF_PROG_TYPE_CGROUP_SKB programs, which we require * e) the BPF implementation in the kernel supports the BPF_PROG_DETACH call, which we require */ if (supported >= 0) return supported; if (geteuid() != 0) { bpf_firewall_unsupported_reason = log_debug_errno(SYNTHETIC_ERRNO(EACCES), "Not enough privileges, BPF firewalling is not supported."); return supported = BPF_FIREWALL_UNSUPPORTED; } r = cg_unified_controller(SYSTEMD_CGROUP_CONTROLLER); if (r < 0) return log_error_errno(r, "Can't determine whether the unified hierarchy is used: %m"); if (r == 0) { bpf_firewall_unsupported_reason = log_debug_errno(SYNTHETIC_ERRNO(EUCLEAN), "Not running with unified cgroups, BPF firewalling is not supported."); return supported = BPF_FIREWALL_UNSUPPORTED; } fd = bpf_map_new(BPF_MAP_TYPE_LPM_TRIE, offsetof(struct bpf_lpm_trie_key, data) + sizeof(uint64_t), sizeof(uint64_t), 1, BPF_F_NO_PREALLOC); if (fd < 0) { bpf_firewall_unsupported_reason = log_debug_errno(fd, "Can't allocate BPF LPM TRIE map, BPF firewalling is not supported: %m"); return supported = BPF_FIREWALL_UNSUPPORTED; } safe_close(fd); r = bpf_program_new(BPF_PROG_TYPE_CGROUP_SKB, &program); if (r < 0) { bpf_firewall_unsupported_reason = log_debug_errno(r, "Can't allocate CGROUP SKB BPF program, BPF firewalling is not supported: %m"); return supported = BPF_FIREWALL_UNSUPPORTED; } r = bpf_program_add_instructions(program, trivial, ELEMENTSOF(trivial)); if (r < 0) { bpf_firewall_unsupported_reason = log_debug_errno(r, "Can't add trivial instructions to CGROUP SKB BPF program, BPF firewalling is not supported: %m"); return supported = BPF_FIREWALL_UNSUPPORTED; } r = bpf_program_load_kernel(program, NULL, 0); if (r < 0) { bpf_firewall_unsupported_reason = log_debug_errno(r, "Can't load kernel CGROUP SKB BPF program, BPF firewalling is not supported: %m"); return supported = BPF_FIREWALL_UNSUPPORTED; } /* Unfortunately the kernel allows us to create BPF_PROG_TYPE_CGROUP_SKB programs even when CONFIG_CGROUP_BPF * is turned off at kernel compilation time. This sucks of course: why does it allow us to create a cgroup BPF * program if we can't do a thing with it later? * * We detect this case by issuing the BPF_PROG_DETACH bpf() call with invalid file descriptors: if * CONFIG_CGROUP_BPF is turned off, then the call will fail early with EINVAL. If it is turned on the * parameters are validated however, and that'll fail with EBADF then. */ attr = (union bpf_attr) { .attach_type = BPF_CGROUP_INET_EGRESS, .target_fd = -1, .attach_bpf_fd = -1, }; if (bpf(BPF_PROG_DETACH, &attr, sizeof(attr)) < 0) { if (errno != EBADF) { bpf_firewall_unsupported_reason = log_debug_errno(errno, "Didn't get EBADF from BPF_PROG_DETACH, BPF firewalling is not supported: %m"); return supported = BPF_FIREWALL_UNSUPPORTED; } /* YAY! */ } else { log_debug("Wut? Kernel accepted our invalid BPF_PROG_DETACH call? Something is weird, assuming BPF firewalling is broken and hence not supported."); return supported = BPF_FIREWALL_UNSUPPORTED; } /* So now we know that the BPF program is generally available, let's see if BPF_F_ALLOW_MULTI is also supported * (which was added in kernel 4.15). We use a similar logic as before, but this time we use the BPF_PROG_ATTACH * bpf() call and the BPF_F_ALLOW_MULTI flags value. Since the flags are checked early in the system call we'll * get EINVAL if it's not supported, and EBADF as before if it is available. */ attr = (union bpf_attr) { .attach_type = BPF_CGROUP_INET_EGRESS, .target_fd = -1, .attach_bpf_fd = -1, .attach_flags = BPF_F_ALLOW_MULTI, }; if (bpf(BPF_PROG_ATTACH, &attr, sizeof(attr)) < 0) { if (errno == EBADF) { log_debug_errno(errno, "Got EBADF when using BPF_F_ALLOW_MULTI, which indicates it is supported. Yay!"); return supported = BPF_FIREWALL_SUPPORTED_WITH_MULTI; } if (errno == EINVAL) log_debug_errno(errno, "Got EINVAL error when using BPF_F_ALLOW_MULTI, which indicates it's not supported."); else log_debug_errno(errno, "Got unexpected error when using BPF_F_ALLOW_MULTI, assuming it's not supported: %m"); return supported = BPF_FIREWALL_SUPPORTED; } else { log_debug("Wut? Kernel accepted our invalid BPF_PROG_ATTACH+BPF_F_ALLOW_MULTI call? Something is weird, assuming BPF firewalling is broken and hence not supported."); return supported = BPF_FIREWALL_UNSUPPORTED; } } void emit_bpf_firewall_warning(Unit *u) { static bool warned = false; if (!warned) { bool quiet = bpf_firewall_unsupported_reason == -EPERM && detect_container(); log_unit_full(u, quiet ? LOG_DEBUG : LOG_WARNING, bpf_firewall_unsupported_reason, "unit configures an IP firewall, but %s.\n" "(This warning is only shown for the first unit using IP firewalling.)", getuid() != 0 ? "not running as root" : "the local system does not support BPF/cgroup firewalling"); warned = true; } }