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bpf: beef up bpf detection, check if BPF_F_ALLOW_MULTI is supported

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This improves the BPF/cgroup detection logic, and looks whether
BPF_ALLOW_MULTI is supported. This flag allows execution of multiple
BPF filters in a recursive fashion for a whole cgroup tree. It enables
us to properly report IP accounting for slice units, as well as
delegation of BPF support to units without breaking our own IP
accounting.
This commit is contained in:
Lennart Poettering 2018-02-16 11:55:33 +01:00
parent 8b15fca85b
commit 2ae7ee58fa
6 changed files with 62 additions and 19 deletions
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60
src/core/bpf-firewall.c
View File

@ -493,7 +493,7 @@ int bpf_firewall_compile(Unit *u) {
r = bpf_firewall_supported();
if (r < 0)
return r;
if (r == 0) {
if (r == BPF_FIREWALL_UNSUPPORTED) {
log_debug("BPF firewalling not supported on this manager, proceeding without.");
return -EOPNOTSUPP;
}
@ -555,7 +555,7 @@ int bpf_firewall_install(Unit *u) {
r = bpf_firewall_supported();
if (r < 0)
return r;
if (r == 0) {
if (r == BPF_FIREWALL_UNSUPPORTED) {
log_debug("BPF firewalling not supported on this manager, proceeding without.");
return -EOPNOTSUPP;
}
@ -667,7 +667,7 @@ int bpf_firewall_supported(void) {
if (geteuid() != 0) {
log_debug("Not enough privileges, BPF firewalling is not supported.");
return supported = false;
return supported = BPF_FIREWALL_UNSUPPORTED;
}
r = cg_unified_controller(SYSTEMD_CGROUP_CONTROLLER);
@ -675,7 +675,7 @@ int bpf_firewall_supported(void) {
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 = false;
return supported = BPF_FIREWALL_UNSUPPORTED;
}
fd = bpf_map_new(BPF_MAP_TYPE_LPM_TRIE,
@ -685,26 +685,26 @@ int bpf_firewall_supported(void) {
BPF_F_NO_PREALLOC);
if (fd < 0) {
log_debug_errno(r, "Can't allocate BPF LPM TRIE map, BPF firewalling is not supported: %m");
return supported = false;
return supported = BPF_FIREWALL_UNSUPPORTED;
}
safe_close(fd);
if (bpf_program_new(BPF_PROG_TYPE_CGROUP_SKB, &program) < 0) {
log_debug_errno(r, "Can't allocate CGROUP SKB BPF program, BPF firewalling is not supported: %m");
return supported = false;
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 = false;
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 = false;
return supported = BPF_FIREWALL_UNSUPPORTED;
}
/* Unfortunately the kernel allows us to create BPF_PROG_TYPE_CGROUP_SKB programs even when CONFIG_CGROUP_BPF
@ -723,12 +723,44 @@ int bpf_firewall_supported(void) {
r = bpf(BPF_PROG_ATTACH, &attr, sizeof(attr));
if (r < 0) {
if (errno == EBADF) /* YAY! */
return supported = true;
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;
}
log_debug_errno(errno, "Didn't get EBADF from BPF_PROG_ATTACH, BPF firewalling is not supported: %m");
} else
log_debug("Wut? kernel accepted our invalid BPF_PROG_ATTACH call? Something is weird, assuming BPF firewalling is broken and hence not supported.");
/* 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;
}
return supported = false;
/* 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,
};
r = bpf(BPF_PROG_ATTACH, &attr, sizeof(attr));
if (r < 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;
}
}

6
src/core/bpf-firewall.h
View File

@ -24,6 +24,12 @@
#include "unit.h"
enum {
BPF_FIREWALL_UNSUPPORTED = 0,
BPF_FIREWALL_SUPPORTED = 1,
BPF_FIREWALL_SUPPORTED_WITH_MULTI = 2,
};
int bpf_firewall_supported(void);
int bpf_firewall_compile(Unit *u);

2
src/core/dbus-cgroup.c
View File

@ -1167,7 +1167,7 @@ int bus_cgroup_set_property(
r = bpf_firewall_supported();
if (r < 0)
return r;
if (r == 0) {
if (r == BPF_FIREWALL_UNSUPPORTED) {
static bool warned = false;
log_full(warned ? LOG_DEBUG : LOG_WARNING,

2
src/core/ip-address-access.c
View File

@ -156,7 +156,7 @@ int config_parse_ip_address_access(
r = bpf_firewall_supported();
if (r < 0)
return r;
if (r == 0) {
if (r == BPF_FIREWALL_UNSUPPORTED) {
static bool warned = false;
log_full(warned ? LOG_DEBUG : LOG_WARNING,

4
src/core/socket.c
View File

@ -1521,7 +1521,7 @@ static int socket_address_listen_in_cgroup(
r = bpf_firewall_supported();
if (r < 0)
return r;
if (r == 0) /* If BPF firewalling isn't supported anyway — there's no point in this forking complexity */
if (r == BPF_FIREWALL_UNSUPPORTED) /* If BPF firewalling isn't supported anyway — there's no point in this forking complexity */
goto shortcut;
if (socketpair(AF_UNIX, SOCK_SEQPACKET|SOCK_CLOEXEC, 0, pair) < 0)
@ -2865,7 +2865,7 @@ static int socket_accept_in_cgroup(Socket *s, SocketPort *p, int fd) {
r = bpf_firewall_supported();
if (r < 0)
return r;
if (r == 0)
if (r == BPF_FIREWALL_UNSUPPORTED)
goto shortcut;
if (socketpair(AF_UNIX, SOCK_SEQPACKET|SOCK_CLOEXEC, 0, pair) < 0)

7
src/test/test-bpf.c
View File

@ -71,12 +71,17 @@ int main(int argc, char *argv[]) {
}
r = bpf_firewall_supported();
if (r == 0) {
if (r == BPF_FIREWALL_UNSUPPORTED) {
log_notice("BPF firewalling not supported, skipping");
return EXIT_TEST_SKIP;
}
assert_se(r > 0);
if (r == BPF_FIREWALL_SUPPORTED_WITH_MULTI)
log_notice("BPF firewalling with BPF_F_ALLOW_MULTI supported. Yay!");
else
log_notice("BPF firewalling (though without BPF_F_ALLOW_MULTI) supported. Good.");
r = bpf_program_load_kernel(p, log_buf, ELEMENTSOF(log_buf));
assert(r >= 0);