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-rw-r--r--src/core/bpf-lsm.c364
1 files changed, 364 insertions, 0 deletions
diff --git a/src/core/bpf-lsm.c b/src/core/bpf-lsm.c
new file mode 100644
index 0000000..a3726d9
--- /dev/null
+++ b/src/core/bpf-lsm.c
@@ -0,0 +1,364 @@
+/* SPDX-License-Identifier: LGPL-2.1-or-later */
+
+#include <errno.h>
+#include <fcntl.h>
+#include <linux/types.h>
+#include <sys/resource.h>
+#include <sys/stat.h>
+#include <sys/time.h>
+#include <sys/types.h>
+#include <unistd.h>
+
+#include "alloc-util.h"
+#include "bpf-lsm.h"
+#include "cgroup-util.h"
+#include "fd-util.h"
+#include "fileio.h"
+#include "filesystems.h"
+#include "log.h"
+#include "manager.h"
+#include "mkdir.h"
+#include "nulstr-util.h"
+#include "stat-util.h"
+#include "strv.h"
+
+#if BPF_FRAMEWORK
+/* libbpf, clang and llc compile time dependencies are satisfied */
+#include "bpf-dlopen.h"
+#include "bpf-link.h"
+#include "bpf-util.h"
+#include "bpf/restrict_fs/restrict-fs-skel.h"
+
+#define CGROUP_HASH_SIZE_MAX 2048
+
+static struct restrict_fs_bpf *restrict_fs_bpf_free(struct restrict_fs_bpf *obj) {
+ /* restrict_fs_bpf__destroy handles object == NULL case */
+ (void) restrict_fs_bpf__destroy(obj);
+
+ return NULL;
+}
+
+DEFINE_TRIVIAL_CLEANUP_FUNC(struct restrict_fs_bpf *, restrict_fs_bpf_free);
+
+static bool bpf_can_link_lsm_program(struct bpf_program *prog) {
+ _cleanup_(bpf_link_freep) struct bpf_link *link = NULL;
+
+ assert(prog);
+
+ link = sym_bpf_program__attach_lsm(prog);
+
+ /* If bpf_program__attach_lsm fails the resulting value stores libbpf error code instead of memory
+ * pointer. That is the case when the helper is called on architectures where BPF trampoline (hence
+ * BPF_LSM_MAC attach type) is not supported. */
+ return sym_libbpf_get_error(link) == 0;
+}
+
+static int prepare_restrict_fs_bpf(struct restrict_fs_bpf **ret_obj) {
+ _cleanup_(restrict_fs_bpf_freep) struct restrict_fs_bpf *obj = NULL;
+ _cleanup_close_ int inner_map_fd = -1;
+ int r;
+
+ assert(ret_obj);
+
+ obj = restrict_fs_bpf__open();
+ if (!obj)
+ return log_error_errno(errno, "bpf-lsm: Failed to open BPF object: %m");
+
+ /* TODO Maybe choose a number based on runtime information? */
+ r = sym_bpf_map__set_max_entries(obj->maps.cgroup_hash, CGROUP_HASH_SIZE_MAX);
+ assert(r <= 0);
+ if (r < 0)
+ return log_error_errno(r, "bpf-lsm: Failed to resize BPF map '%s': %m",
+ sym_bpf_map__name(obj->maps.cgroup_hash));
+
+ /* Dummy map to satisfy the verifier */
+ inner_map_fd = compat_bpf_map_create(BPF_MAP_TYPE_HASH, NULL, sizeof(uint32_t), sizeof(uint32_t), 128U, NULL);
+ if (inner_map_fd < 0)
+ return log_error_errno(errno, "bpf-lsm: Failed to create BPF map: %m");
+
+ r = sym_bpf_map__set_inner_map_fd(obj->maps.cgroup_hash, inner_map_fd);
+ assert(r <= 0);
+ if (r < 0)
+ return log_error_errno(r, "bpf-lsm: Failed to set inner map fd: %m");
+
+ r = restrict_fs_bpf__load(obj);
+ assert(r <= 0);
+ if (r < 0)
+ return log_error_errno(r, "bpf-lsm: Failed to load BPF object: %m");
+
+ *ret_obj = TAKE_PTR(obj);
+
+ return 0;
+}
+
+static int mac_bpf_use(void) {
+ _cleanup_free_ char *lsm_list = NULL;
+ static int cached_use = -1;
+ int r;
+
+ if (cached_use >= 0)
+ return cached_use;
+
+ cached_use = 0;
+
+ r = read_one_line_file("/sys/kernel/security/lsm", &lsm_list);
+ if (r < 0) {
+ if (r != -ENOENT)
+ log_notice_errno(r, "bpf-lsm: Failed to read /sys/kernel/security/lsm, assuming bpf is unavailable: %m");
+ return 0;
+ }
+
+ for (const char *p = lsm_list;;) {
+ _cleanup_free_ char *word = NULL;
+
+ r = extract_first_word(&p, &word, ",", 0);
+ if (r == 0)
+ return 0;
+ if (r == -ENOMEM)
+ return log_oom();
+ if (r < 0) {
+ log_notice_errno(r, "bpf-lsm: Failed to parse /sys/kernel/security/lsm, assuming bpf is unavailable: %m");
+ return 0;
+ }
+
+ if (streq(word, "bpf"))
+ return cached_use = 1;
+ }
+}
+
+bool lsm_bpf_supported(bool initialize) {
+ _cleanup_(restrict_fs_bpf_freep) struct restrict_fs_bpf *obj = NULL;
+ static int supported = -1;
+ int r;
+
+ if (supported >= 0)
+ return supported;
+ if (!initialize)
+ return false;
+
+ if (!cgroup_bpf_supported())
+ return (supported = false);
+
+ r = mac_bpf_use();
+ if (r < 0) {
+ log_warning_errno(r, "bpf-lsm: Can't determine whether the BPF LSM module is used: %m");
+ return (supported = false);
+ }
+
+ if (r == 0) {
+ log_info_errno(SYNTHETIC_ERRNO(EOPNOTSUPP),
+ "bpf-lsm: BPF LSM hook not enabled in the kernel, BPF LSM not supported");
+ return (supported = false);
+ }
+
+ r = prepare_restrict_fs_bpf(&obj);
+ if (r < 0)
+ return (supported = false);
+
+ if (!bpf_can_link_lsm_program(obj->progs.restrict_filesystems)) {
+ log_warning_errno(SYNTHETIC_ERRNO(EOPNOTSUPP),
+ "bpf-lsm: Failed to link program; assuming BPF LSM is not available");
+ return (supported = false);
+ }
+
+ return (supported = true);
+}
+
+int lsm_bpf_setup(Manager *m) {
+ _cleanup_(restrict_fs_bpf_freep) struct restrict_fs_bpf *obj = NULL;
+ _cleanup_(bpf_link_freep) struct bpf_link *link = NULL;
+ int r;
+
+ assert(m);
+
+ r = prepare_restrict_fs_bpf(&obj);
+ if (r < 0)
+ return r;
+
+ link = sym_bpf_program__attach_lsm(obj->progs.restrict_filesystems);
+ r = sym_libbpf_get_error(link);
+ if (r != 0)
+ return log_error_errno(r, "bpf-lsm: Failed to link '%s' LSM BPF program: %m",
+ sym_bpf_program__name(obj->progs.restrict_filesystems));
+
+ log_info("bpf-lsm: LSM BPF program attached");
+
+ obj->links.restrict_filesystems = TAKE_PTR(link);
+ m->restrict_fs = TAKE_PTR(obj);
+
+ return 0;
+}
+
+int lsm_bpf_unit_restrict_filesystems(Unit *u, const Set *filesystems, bool allow_list) {
+ uint32_t dummy_value = 1, zero = 0;
+ const char *fs;
+ const statfs_f_type_t *magic;
+ int r;
+
+ assert(filesystems);
+ assert(u);
+
+ if (!u->manager->restrict_fs)
+ return log_unit_error_errno(u, SYNTHETIC_ERRNO(EINVAL),
+ "bpf-lsm: BPF LSM object is not installed, has setup failed?");
+
+ int inner_map_fd = compat_bpf_map_create(
+ BPF_MAP_TYPE_HASH,
+ NULL,
+ sizeof(uint32_t),
+ sizeof(uint32_t),
+ 128U, /* Should be enough for all filesystem types */
+ NULL);
+ if (inner_map_fd < 0)
+ return log_unit_error_errno(u, errno, "bpf-lsm: Failed to create inner BPF map: %m");
+
+ int outer_map_fd = sym_bpf_map__fd(u->manager->restrict_fs->maps.cgroup_hash);
+ if (outer_map_fd < 0)
+ return log_unit_error_errno(u, errno, "bpf-lsm: Failed to get BPF map fd: %m");
+
+ if (sym_bpf_map_update_elem(outer_map_fd, &u->cgroup_id, &inner_map_fd, BPF_ANY) != 0)
+ return log_unit_error_errno(u, errno, "bpf-lsm: Error populating BPF map: %m");
+
+ uint32_t allow = allow_list;
+
+ /* Use key 0 to store whether this is an allow list or a deny list */
+ if (sym_bpf_map_update_elem(inner_map_fd, &zero, &allow, BPF_ANY) != 0)
+ return log_unit_error_errno(u, errno, "bpf-lsm: Error initializing map: %m");
+
+ SET_FOREACH(fs, filesystems) {
+ r = fs_type_from_string(fs, &magic);
+ if (r < 0) {
+ log_unit_warning(u, "bpf-lsm: Invalid filesystem name '%s', ignoring.", fs);
+ continue;
+ }
+
+ log_unit_debug(u, "bpf-lsm: Restricting filesystem access to '%s'", fs);
+
+ for (int i = 0; i < FILESYSTEM_MAGIC_MAX; i++) {
+ if (magic[i] == 0)
+ break;
+
+ if (sym_bpf_map_update_elem(inner_map_fd, &magic[i], &dummy_value, BPF_ANY) != 0) {
+ r = log_unit_error_errno(u, errno, "bpf-lsm: Failed to update BPF map: %m");
+
+ if (sym_bpf_map_delete_elem(outer_map_fd, &u->cgroup_id) != 0)
+ log_unit_debug_errno(u, errno, "bpf-lsm: Failed to delete cgroup entry from BPF map: %m");
+
+ return r;
+ }
+ }
+ }
+
+ return 0;
+}
+
+int lsm_bpf_cleanup(const Unit *u) {
+ assert(u);
+ assert(u->manager);
+
+ /* If we never successfully detected support, there is nothing to clean up. */
+ if (!lsm_bpf_supported(/* initialize = */ false))
+ return 0;
+
+ if (!u->manager->restrict_fs)
+ return 0;
+
+ if (u->cgroup_id == 0)
+ return 0;
+
+ int fd = sym_bpf_map__fd(u->manager->restrict_fs->maps.cgroup_hash);
+ if (fd < 0)
+ return log_unit_error_errno(u, errno, "bpf-lsm: Failed to get BPF map fd: %m");
+
+ if (sym_bpf_map_delete_elem(fd, &u->cgroup_id) != 0 && errno != ENOENT)
+ return log_unit_debug_errno(u, errno, "bpf-lsm: Failed to delete cgroup entry from LSM BPF map: %m");
+
+ return 0;
+}
+
+int lsm_bpf_map_restrict_fs_fd(Unit *unit) {
+ assert(unit);
+ assert(unit->manager);
+
+ if (!unit->manager->restrict_fs)
+ return -ENOMEDIUM;
+
+ return sym_bpf_map__fd(unit->manager->restrict_fs->maps.cgroup_hash);
+}
+
+void lsm_bpf_destroy(struct restrict_fs_bpf *prog) {
+ restrict_fs_bpf__destroy(prog);
+}
+#else /* ! BPF_FRAMEWORK */
+bool lsm_bpf_supported(bool initialize) {
+ return false;
+}
+
+int lsm_bpf_setup(Manager *m) {
+ return log_debug_errno(SYNTHETIC_ERRNO(EOPNOTSUPP), "bpf-lsm: Failed to set up LSM BPF: %m");
+}
+
+int lsm_bpf_unit_restrict_filesystems(Unit *u, const Set *filesystems, const bool allow_list) {
+ return log_unit_debug_errno(u, SYNTHETIC_ERRNO(EOPNOTSUPP), "bpf-lsm: Failed to restrict filesystems using LSM BPF: %m");
+}
+
+int lsm_bpf_cleanup(const Unit *u) {
+ return 0;
+}
+
+int lsm_bpf_map_restrict_fs_fd(Unit *unit) {
+ return -ENOMEDIUM;
+}
+
+void lsm_bpf_destroy(struct restrict_fs_bpf *prog) {
+ return;
+}
+#endif
+
+int lsm_bpf_parse_filesystem(
+ const char *name,
+ Set **filesystems,
+ FilesystemParseFlags flags,
+ const char *unit,
+ const char *filename,
+ unsigned line) {
+ int r;
+
+ assert(name);
+ assert(filesystems);
+
+ if (name[0] == '@') {
+ const FilesystemSet *set;
+ const char *i;
+
+ set = filesystem_set_find(name);
+ if (!set) {
+ log_syntax(unit, flags & FILESYSTEM_PARSE_LOG ? LOG_WARNING : LOG_DEBUG, filename, line, 0,
+ "bpf-lsm: Unknown filesystem group, ignoring: %s", name);
+ return 0;
+ }
+
+ NULSTR_FOREACH(i, set->value) {
+ /* Call ourselves again, for the group to parse. Note that we downgrade logging here
+ * (i.e. take away the FILESYSTEM_PARSE_LOG flag) since any issues in the group table
+ * are our own problem, not a problem in user configuration data and we shouldn't
+ * pretend otherwise by complaining about them. */
+ r = lsm_bpf_parse_filesystem(i, filesystems, flags &~ FILESYSTEM_PARSE_LOG, unit, filename, line);
+ if (r < 0)
+ return r;
+ }
+ } else {
+ /* If we previously wanted to forbid access to a filesystem and now
+ * we want to allow it, then remove it from the list. */
+ if (!(flags & FILESYSTEM_PARSE_INVERT) == !!(flags & FILESYSTEM_PARSE_ALLOW_LIST)) {
+ r = set_put_strdup(filesystems, name);
+ if (r == -ENOMEM)
+ return flags & FILESYSTEM_PARSE_LOG ? log_oom() : -ENOMEM;
+ if (r < 0 && r != -EEXIST) /* When already in set, ignore */
+ return r;
+ } else
+ free(set_remove(*filesystems, name));
+ }
+
+ return 0;
+}
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