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bpf-firewall: optimization for IPAddressXYZ="any" (and unprivileged users)

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This is a workaround to make IPAddressDeny=any/IPAddressAllow=any work
for non-root users that have CAP_NET_ADMIN. "any" was chosen since
all or nothing network access is one of the most common use cases for
isolation.

Allocating BPF LPM TRIE maps require CAP_SYS_ADMIN while BPF_PROG_TYPE_CGROUP_SKB
only needs CAP_NET_ADMIN. In the case of IPAddressXYZ="any" we can just
consistently return false/true to avoid allocating the map and limit the user
to having CAP_NET_ADMIN.
This commit is contained in:
Anita Zhang 2019-05-20 14:43:53 -07:00 committed by Lennart Poettering
parent e48fcfef06
commit 4c1567f29a
3 changed files with 83 additions and 36 deletions
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97
src/core/bpf-firewall.c
View File

@ -125,10 +125,30 @@ static int add_lookup_instructions(
return 0;
}
static int add_instructions_for_ip_any(
BPFProgram *p,
int verdict) {
int r;
assert(p);
struct bpf_insn insn[] = {
BPF_ALU32_IMM(BPF_OR, BPF_REG_8, verdict),
};
r = bpf_program_add_instructions(p, insn, 1);
if (r < 0)
return r;
return 0;
}
static int bpf_firewall_compile_bpf(
Unit *u,
bool is_ingress,
BPFProgram **ret) {
BPFProgram **ret,
bool ip_allow_any,
bool ip_deny_any) {
struct bpf_insn pre_insn[] = {
/*
@ -187,7 +207,9 @@ static int bpf_firewall_compile_bpf(
u->ipv4_allow_map_fd >= 0 ||
u->ipv6_allow_map_fd >= 0 ||
u->ipv4_deny_map_fd >= 0 ||
u->ipv6_deny_map_fd >= 0;
u->ipv6_deny_map_fd >= 0 ||
ip_allow_any ||
ip_deny_any;
if (accounting_map_fd < 0 && !access_enabled) {
*ret = NULL;
@ -234,6 +256,18 @@ static int bpf_firewall_compile_bpf(
if (r < 0)
return r;
}
if (ip_allow_any) {
r = add_instructions_for_ip_any(p, ACCESS_ALLOWED);
if (r < 0)
return r;
}
if (ip_deny_any) {
r = add_instructions_for_ip_any(p, ACCESS_DENIED);
if (r < 0)
return r;
}
}
r = bpf_program_add_instructions(p, post_insn, ELEMENTSOF(post_insn));
@ -375,15 +409,18 @@ static int bpf_firewall_prepare_access_maps(
Unit *u,
int verdict,
int *ret_ipv4_map_fd,
int *ret_ipv6_map_fd) {
int *ret_ipv6_map_fd,
bool *ret_has_any) {
_cleanup_close_ int ipv4_map_fd = -1, ipv6_map_fd = -1;
size_t n_ipv4 = 0, n_ipv6 = 0;
IPAddressAccessItem *list;
Unit *p;
int r;
assert(ret_ipv4_map_fd);
assert(ret_ipv6_map_fd);
assert(ret_has_any);
for (p = u; p; p = UNIT_DEREF(p->slice)) {
CGroupContext *cc;
@ -392,7 +429,16 @@ static int bpf_firewall_prepare_access_maps(
if (!cc)
continue;
bpf_firewall_count_access_items(verdict == ACCESS_ALLOWED ? cc->ip_address_allow : cc->ip_address_deny, &n_ipv4, &n_ipv6);
list = verdict == ACCESS_ALLOWED ? cc->ip_address_allow : cc->ip_address_deny;
bpf_firewall_count_access_items(list, &n_ipv4, &n_ipv6);
/* Skip making the LPM trie map in cases where we are using "any" in order to hack around
* needing CAP_SYS_ADMIN for allocating LPM trie map. */
if (ip_address_access_item_is_any(list)) {
*ret_has_any = true;
return 0;
}
}
if (n_ipv4 > 0) {
@ -432,6 +478,7 @@ static int bpf_firewall_prepare_access_maps(
*ret_ipv4_map_fd = TAKE_FD(ipv4_map_fd);
*ret_ipv6_map_fd = TAKE_FD(ipv6_map_fd);
*ret_has_any = false;
return 0;
}
@ -473,6 +520,7 @@ static int bpf_firewall_prepare_accounting_maps(Unit *u, bool enabled, int *fd_i
int bpf_firewall_compile(Unit *u) {
CGroupContext *cc;
int r, supported;
bool ip_allow_any = false, ip_deny_any = false;
assert(u);
@ -515,11 +563,11 @@ int bpf_firewall_compile(Unit *u) {
* 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);
r = bpf_firewall_prepare_access_maps(u, ACCESS_ALLOWED, &u->ipv4_allow_map_fd, &u->ipv6_allow_map_fd, &ip_allow_any);
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);
r = bpf_firewall_prepare_access_maps(u, ACCESS_DENIED, &u->ipv4_deny_map_fd, &u->ipv6_deny_map_fd, &ip_deny_any);
if (r < 0)
return log_unit_error_errno(u, r, "Preparation of eBPF deny maps failed: %m");
}
@ -528,11 +576,11 @@ int bpf_firewall_compile(Unit *u) {
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);
r = bpf_firewall_compile_bpf(u, true, &u->ip_bpf_ingress, ip_allow_any, ip_deny_any);
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);
r = bpf_firewall_compile_bpf(u, false, &u->ip_bpf_egress, ip_allow_any, ip_deny_any);
if (r < 0)
return log_unit_error_errno(u, r, "Compilation for egress BPF program failed: %m");
@ -653,27 +701,17 @@ int bpf_firewall_supported(void) {
_cleanup_(bpf_program_unrefp) BPFProgram *program = NULL;
static int supported = -1;
union bpf_attr attr;
int fd, r;
int r;
/* Checks whether BPF firewalling is supported. For this, we check five things:
/* Checks whether BPF firewalling is supported. For this, we check the following 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
* - whether the unified hierarchy is being used
* - the BPF implementation in the kernel supports BPF_PROG_TYPE_CGROUP_SKB programs, which we require
* - 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");
@ -684,19 +722,6 @@ int bpf_firewall_supported(void) {
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 =

18
src/core/ip-address-access.c
View File

@ -188,3 +188,21 @@ IPAddressAccessItem* ip_address_access_reduce(IPAddressAccessItem *first) {
return first;
}
bool ip_address_access_item_is_any(IPAddressAccessItem *first) {
/* Check for exactly two entries */
if (!first || !first->items_next || first->items_next->items_next)
return false;
/* Check both entries cover the full range */
if (first->prefixlen != 0 || first->items_next->prefixlen != 0)
return false;
/* Check that one of them is the IPv4 and the other IPv6 */
if (!((first->family == AF_INET && first->items_next->family == AF_INET6) ||
(first->family == AF_INET6 && first->items_next->family == AF_INET)))
return false;
/* No need to check the actual addresses, they don't matter if the prefix is zero */
return true;
}

4
src/core/ip-address-access.h
View File

@ -19,3 +19,7 @@ CONFIG_PARSER_PROTOTYPE(config_parse_ip_address_access);
IPAddressAccessItem* ip_address_access_free_all(IPAddressAccessItem *first);
IPAddressAccessItem* ip_address_access_reduce(IPAddressAccessItem *first);
/* Returns true if a list consists of only the two items necessary for "any"
* (0.0.0.0/0 and ::/0). */
bool ip_address_access_item_is_any(IPAddressAccessItem *first);