/* SPDX-License-Identifier: LGPL-2.1+ */
#include <arpa/inet.h>
#include <assert.h>
#include <errno.h>
#include <fcntl.h>
#include <linux/libbpf.h>
#include <net/ethernet.h>
#include <net/if.h>
#include <netinet/ip.h>
#include <netinet/ip6.h>
#include <stddef.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <unistd.h>
#include "alloc-util.h"
#include "bpf-firewall.h"
#include "bpf-program.h"
#include "fd-util.h"
#include "ip-address-access.h"
#include "unit.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) {
log_debug("BPF firewalling not supported on this manager, proceeding without.");
return -EOPNOTSUPP;
}
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. */
log_debug("BPF_F_ALLOW_MULTI is not supported on this manager, not doing BPF firewall on slice units.");
return -EOPNOTSUPP;
}
/* 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_error_errno(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_error_errno(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_error_errno(r, "Preparation of eBPF accounting maps failed: %m");
r = bpf_firewall_compile_bpf(u, true, &u->ip_bpf_ingress);
if (r < 0)
return log_error_errno(r, "Compilation for ingress BPF program failed: %m");
r = bpf_firewall_compile_bpf(u, false, &u->ip_bpf_egress);
if (r < 0)
return log_error_errno(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_debug("BPF firewalling not supported on this manager, proceeding without.");
return -EOPNOTSUPP;
}
if (supported != BPF_FIREWALL_SUPPORTED_WITH_MULTI && u->type == UNIT_SLICE) {
log_debug("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_error_errno(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_error_errno(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_error_errno(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);
}
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_ATTACH call, which we require
*
*/
if (supported >= 0)
return supported;
if (geteuid() != 0) {
log_debug("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) {
log_debug("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) {
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) {
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) {
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) {
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_ATTACH 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_ATTACH, &attr, sizeof(attr)) < 0) {
if (errno != EBADF) {
log_debug_errno(errno, "Didn't get EBADF from BPF_PROG_ATTACH, BPF firewalling is not supported: %m");
return supported = BPF_FIREWALL_UNSUPPORTED;
}
/* YAY! */
} else {
log_debug("Wut? Kernel accepted our invalid BPF_PROG_ATTACH 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
* BPF_F_ALLOW_MULTI. 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;
}
}