diff options
Diffstat (limited to 'src/shared/bpf-program.c')
| -rw-r--r-- | src/shared/bpf-program.c | 513 |
1 files changed, 513 insertions, 0 deletions
diff --git a/src/shared/bpf-program.c b/src/shared/bpf-program.c new file mode 100644 index 0000000..bbdd4f6 --- /dev/null +++ b/src/shared/bpf-program.c @@ -0,0 +1,513 @@ +/* SPDX-License-Identifier: LGPL-2.1-or-later */ + +#include <fcntl.h> +#include <sys/stat.h> +#include <sys/types.h> +#include <unistd.h> + +#include "alloc-util.h" +#include "bpf-program.h" +#include "errno-util.h" +#include "escape.h" +#include "fd-util.h" +#include "memory-util.h" +#include "missing_syscall.h" +#include "path-util.h" +#include "serialize.h" +#include "string-table.h" + +static const char *const bpf_cgroup_attach_type_table[__MAX_BPF_ATTACH_TYPE] = { + [BPF_CGROUP_INET_INGRESS] = "ingress", + [BPF_CGROUP_INET_EGRESS] = "egress", + [BPF_CGROUP_INET_SOCK_CREATE] = "sock_create", + [BPF_CGROUP_SOCK_OPS] = "sock_ops", + [BPF_CGROUP_DEVICE] = "device", + [BPF_CGROUP_INET4_BIND] = "bind4", + [BPF_CGROUP_INET6_BIND] = "bind6", + [BPF_CGROUP_INET4_CONNECT] = "connect4", + [BPF_CGROUP_INET6_CONNECT] = "connect6", + [BPF_CGROUP_INET4_POST_BIND] = "post_bind4", + [BPF_CGROUP_INET6_POST_BIND] = "post_bind6", + [BPF_CGROUP_UDP4_SENDMSG] = "sendmsg4", + [BPF_CGROUP_UDP6_SENDMSG] = "sendmsg6", + [BPF_CGROUP_SYSCTL] = "sysctl", + [BPF_CGROUP_UDP4_RECVMSG] = "recvmsg4", + [BPF_CGROUP_UDP6_RECVMSG] = "recvmsg6", + [BPF_CGROUP_GETSOCKOPT] = "getsockopt", + [BPF_CGROUP_SETSOCKOPT] = "setsockopt", +}; + +DEFINE_STRING_TABLE_LOOKUP(bpf_cgroup_attach_type, int); + +DEFINE_HASH_OPS_WITH_KEY_DESTRUCTOR(bpf_program_hash_ops, void, trivial_hash_func, trivial_compare_func, bpf_program_free); + +BPFProgram *bpf_program_free(BPFProgram *p) { + if (!p) + return NULL; + /* Unfortunately, the kernel currently doesn't implicitly detach BPF programs from their cgroups when the last + * fd to the BPF program is closed. This has nasty side-effects since this means that abnormally terminated + * programs that attached one of their BPF programs to a cgroup will leave this program pinned for good with + * zero chance of recovery, until the cgroup is removed. This is particularly problematic if the cgroup in + * question is the root cgroup (or any other cgroup belonging to a service that cannot be restarted during + * operation, such as dbus), as the memory for the BPF program can only be reclaimed through a reboot. To + * counter this, we track closely to which cgroup a program was attached to and will detach it on our own + * whenever we close the BPF fd. */ + (void) bpf_program_cgroup_detach(p); + + safe_close(p->kernel_fd); + free(p->prog_name); + free(p->instructions); + free(p->attached_path); + + return mfree(p); +} + + /* struct bpf_prog_info info must be initialized since its value is both input and output + * for BPF_OBJ_GET_INFO_BY_FD syscall. */ +static int bpf_program_get_info_by_fd(int prog_fd, struct bpf_prog_info *info, uint32_t info_len) { + union bpf_attr attr; + + /* Explicitly memset to zero since some compilers may produce non-zero-initialized padding when + * structured initialization is used. + * Refer to https://github.com/systemd/systemd/issues/18164 + */ + zero(attr); + attr.info.bpf_fd = prog_fd; + attr.info.info_len = info_len; + attr.info.info = PTR_TO_UINT64(info); + + return RET_NERRNO(bpf(BPF_OBJ_GET_INFO_BY_FD, &attr, sizeof(attr))); +} + +int bpf_program_new(uint32_t prog_type, const char *prog_name, BPFProgram **ret) { + _cleanup_(bpf_program_freep) BPFProgram *p = NULL; + _cleanup_free_ char *name = NULL; + + if (prog_name) { + if (strlen(prog_name) >= BPF_OBJ_NAME_LEN) + return -ENAMETOOLONG; + + name = strdup(prog_name); + if (!name) + return -ENOMEM; + } + + p = new(BPFProgram, 1); + if (!p) + return -ENOMEM; + + *p = (BPFProgram) { + .prog_type = prog_type, + .kernel_fd = -EBADF, + .prog_name = TAKE_PTR(name), + }; + + *ret = TAKE_PTR(p); + + return 0; +} + +int bpf_program_new_from_bpffs_path(const char *path, BPFProgram **ret) { + _cleanup_(bpf_program_freep) BPFProgram *p = NULL; + struct bpf_prog_info info = {}; + int r; + + assert(path); + assert(ret); + + p = new(BPFProgram, 1); + if (!p) + return -ENOMEM; + + *p = (BPFProgram) { + .prog_type = BPF_PROG_TYPE_UNSPEC, + .kernel_fd = -EBADF, + }; + + r = bpf_program_load_from_bpf_fs(p, path); + if (r < 0) + return r; + + r = bpf_program_get_info_by_fd(p->kernel_fd, &info, sizeof(info)); + if (r < 0) + return r; + + p->prog_type = info.type; + *ret = TAKE_PTR(p); + + return 0; +} + + +int bpf_program_add_instructions(BPFProgram *p, const struct bpf_insn *instructions, size_t count) { + + assert(p); + + if (p->kernel_fd >= 0) /* don't allow modification after we uploaded things to the kernel */ + return -EBUSY; + + if (!GREEDY_REALLOC(p->instructions, p->n_instructions + count)) + return -ENOMEM; + + memcpy(p->instructions + p->n_instructions, instructions, sizeof(struct bpf_insn) * count); + p->n_instructions += count; + + return 0; +} + +int bpf_program_load_kernel(BPFProgram *p, char *log_buf, size_t log_size) { + union bpf_attr attr; + + assert(p); + + if (p->kernel_fd >= 0) { /* make this idempotent */ + memzero(log_buf, log_size); + return 0; + } + + // FIXME: Clang doesn't 0-pad with structured initialization, causing + // the kernel to reject the bpf_attr as invalid. See: + // https://github.com/torvalds/linux/blob/v5.9/kernel/bpf/syscall.c#L65 + // Ideally it should behave like GCC, so that we can remove these workarounds. + zero(attr); + attr.prog_type = p->prog_type; + attr.insns = PTR_TO_UINT64(p->instructions); + attr.insn_cnt = p->n_instructions; + attr.license = PTR_TO_UINT64("GPL"); + attr.log_buf = PTR_TO_UINT64(log_buf); + attr.log_level = !!log_buf; + attr.log_size = log_size; + if (p->prog_name) + strncpy(attr.prog_name, p->prog_name, BPF_OBJ_NAME_LEN - 1); + + p->kernel_fd = bpf(BPF_PROG_LOAD, &attr, sizeof(attr)); + if (p->kernel_fd < 0) + return -errno; + + return 0; +} + +int bpf_program_load_from_bpf_fs(BPFProgram *p, const char *path) { + union bpf_attr attr; + + assert(p); + + if (p->kernel_fd >= 0) /* don't overwrite an assembled or loaded program */ + return -EBUSY; + + zero(attr); + attr.pathname = PTR_TO_UINT64(path); + + p->kernel_fd = bpf(BPF_OBJ_GET, &attr, sizeof(attr)); + if (p->kernel_fd < 0) + return -errno; + + return 0; +} + +int bpf_program_cgroup_attach(BPFProgram *p, int type, const char *path, uint32_t flags) { + _cleanup_free_ char *copy = NULL; + _cleanup_close_ int fd = -EBADF; + union bpf_attr attr; + int r; + + assert(p); + assert(type >= 0); + assert(path); + + if (!IN_SET(flags, 0, BPF_F_ALLOW_OVERRIDE, BPF_F_ALLOW_MULTI)) + return -EINVAL; + + /* We need to track which cgroup the program is attached to, and we can only track one attachment, hence let's + * refuse this early. */ + if (p->attached_path) { + if (!path_equal(p->attached_path, path)) + return -EBUSY; + if (p->attached_type != type) + return -EBUSY; + if (p->attached_flags != flags) + return -EBUSY; + + /* Here's a shortcut: if we previously attached this program already, then we don't have to do so + * again. Well, with one exception: if we are in BPF_F_ALLOW_OVERRIDE mode then someone else might have + * replaced our program since the last time, hence let's reattach it again, just to be safe. In flags + * == 0 mode this is not an issue since nobody else can replace our program in that case, and in flags + * == BPF_F_ALLOW_MULTI mode any other's program would be installed in addition to ours hence ours + * would remain in effect. */ + if (flags != BPF_F_ALLOW_OVERRIDE) + return 0; + } + + /* Ensure we have a kernel object for this. */ + r = bpf_program_load_kernel(p, NULL, 0); + if (r < 0) + return r; + + copy = strdup(path); + if (!copy) + return -ENOMEM; + + fd = open(path, O_DIRECTORY|O_RDONLY|O_CLOEXEC); + if (fd < 0) + return -errno; + + zero(attr); + attr.attach_type = type; + attr.target_fd = fd; + attr.attach_bpf_fd = p->kernel_fd; + attr.attach_flags = flags; + + if (bpf(BPF_PROG_ATTACH, &attr, sizeof(attr)) < 0) + return -errno; + + free_and_replace(p->attached_path, copy); + p->attached_type = type; + p->attached_flags = flags; + + return 0; +} + +int bpf_program_cgroup_detach(BPFProgram *p) { + _cleanup_close_ int fd = -EBADF; + + assert(p); + + if (!p->attached_path) + return -EUNATCH; + + fd = open(p->attached_path, O_DIRECTORY|O_RDONLY|O_CLOEXEC); + if (fd < 0) { + if (errno != ENOENT) + return -errno; + + /* If the cgroup does not exist anymore, then we don't have to explicitly detach, it got detached + * implicitly by the removal, hence don't complain */ + + } else { + union bpf_attr attr; + + zero(attr); + attr.attach_type = p->attached_type; + attr.target_fd = fd; + attr.attach_bpf_fd = p->kernel_fd; + + if (bpf(BPF_PROG_DETACH, &attr, sizeof(attr)) < 0) + return -errno; + } + + p->attached_path = mfree(p->attached_path); + + return 0; +} + +int bpf_map_new( + const char *name, + enum bpf_map_type type, + size_t key_size, + size_t value_size, + size_t max_entries, + uint32_t flags) { + + union bpf_attr attr; + const char *n = name; + + zero(attr); + attr.map_type = type; + attr.key_size = key_size; + attr.value_size = value_size; + attr.max_entries = max_entries; + attr.map_flags = flags; + + /* The map name is primarily informational for debugging purposes, and typically too short + * to carry the full unit name, hence we employ a trivial lossy escaping to make it fit + * (truncation + only alphanumerical, "." and "_" are allowed as per + * https://www.kernel.org/doc/html/next/bpf/maps.html#usage-notes) */ + for (size_t i = 0; i < sizeof(attr.map_name) - 1 && *n; i++, n++) + attr.map_name[i] = strchr(ALPHANUMERICAL ".", *n) ? *n : '_'; + + return RET_NERRNO(bpf(BPF_MAP_CREATE, &attr, sizeof(attr))); +} + +int bpf_map_update_element(int fd, const void *key, void *value) { + union bpf_attr attr; + + zero(attr); + attr.map_fd = fd; + attr.key = PTR_TO_UINT64(key); + attr.value = PTR_TO_UINT64(value); + + return RET_NERRNO(bpf(BPF_MAP_UPDATE_ELEM, &attr, sizeof(attr))); +} + +int bpf_map_lookup_element(int fd, const void *key, void *value) { + union bpf_attr attr; + + zero(attr); + attr.map_fd = fd; + attr.key = PTR_TO_UINT64(key); + attr.value = PTR_TO_UINT64(value); + + return RET_NERRNO(bpf(BPF_MAP_LOOKUP_ELEM, &attr, sizeof(attr))); +} + +int bpf_program_pin(int prog_fd, const char *bpffs_path) { + union bpf_attr attr; + + zero(attr); + attr.pathname = PTR_TO_UINT64((void *) bpffs_path); + attr.bpf_fd = prog_fd; + + return RET_NERRNO(bpf(BPF_OBJ_PIN, &attr, sizeof(attr))); +} + +int bpf_program_get_id_by_fd(int prog_fd, uint32_t *ret_id) { + struct bpf_prog_info info = {}; + int r; + + assert(ret_id); + + r = bpf_program_get_info_by_fd(prog_fd, &info, sizeof(info)); + if (r < 0) + return r; + + *ret_id = info.id; + + return 0; +}; + +int bpf_program_serialize_attachment( + FILE *f, + FDSet *fds, + const char *key, + BPFProgram *p) { + + _cleanup_free_ char *escaped = NULL; + int copy, r; + + if (!p || !p->attached_path) + return 0; + + assert(p->kernel_fd >= 0); + + escaped = cescape(p->attached_path); + if (!escaped) + return -ENOMEM; + + copy = fdset_put_dup(fds, p->kernel_fd); + if (copy < 0) + return log_error_errno(copy, "Failed to add BPF kernel fd to serialize: %m"); + + r = serialize_item_format( + f, + key, + "%i %s %s", + copy, + bpf_cgroup_attach_type_to_string(p->attached_type), + escaped); + if (r < 0) + return r; + + /* After serialization, let's forget the fact that this program is attached. The attachment — if you + * so will — is now 'owned' by the serialization, and not us anymore. Why does that matter? Because + * of BPF's less-than-ideal lifecycle handling: to detach a program from a cgroup we have to + * explicitly do so, it's not done implicitly on close(). Now, since we are serializing here we don't + * want the program to be detached while freeing things, so that the attachment can be retained after + * deserializing again. bpf_program_free() implicitly detaches things, if attached_path is non-NULL, + * hence we set it to NULL here. */ + + p->attached_path = mfree(p->attached_path); + return 0; +} + +int bpf_program_serialize_attachment_set(FILE *f, FDSet *fds, const char *key, Set *set) { + BPFProgram *p; + int r; + + SET_FOREACH(p, set) { + r = bpf_program_serialize_attachment(f, fds, key, p); + if (r < 0) + return r; + } + + return 0; +} + +int bpf_program_deserialize_attachment(const char *v, FDSet *fds, BPFProgram **bpfp) { + _cleanup_free_ char *sfd = NULL, *sat = NULL, *unescaped = NULL; + _cleanup_(bpf_program_freep) BPFProgram *p = NULL; + _cleanup_close_ int fd = -EBADF; + ssize_t l; + int ifd, at, r; + + assert(v); + assert(bpfp); + + /* Extract first word: the fd number */ + r = extract_first_word(&v, &sfd, NULL, 0); + if (r < 0) + return r; + if (r == 0) + return -EINVAL; + + ifd = parse_fd(sfd); + if (ifd < 0) + return r; + + /* Extract second word: the attach type */ + r = extract_first_word(&v, &sat, NULL, 0); + if (r < 0) + return r; + if (r == 0) + return -EINVAL; + + at = bpf_cgroup_attach_type_from_string(sat); + if (at < 0) + return at; + + /* The rest is the path */ + if (isempty(v)) + return -EINVAL; + + l = cunescape(v, 0, &unescaped); + if (l < 0) + return l; + + fd = fdset_remove(fds, ifd); + if (fd < 0) + return fd; + + p = new(BPFProgram, 1); + if (!p) + return -ENOMEM; + + *p = (BPFProgram) { + .kernel_fd = TAKE_FD(fd), + .prog_type = BPF_PROG_TYPE_UNSPEC, + .attached_path = TAKE_PTR(unescaped), + .attached_type = at, + }; + + if (*bpfp) + bpf_program_free(*bpfp); + + *bpfp = TAKE_PTR(p); + return 0; +} + +int bpf_program_deserialize_attachment_set(const char *v, FDSet *fds, Set **bpfsetp) { + BPFProgram *p = NULL; + int r; + + assert(v); + assert(bpfsetp); + + r = bpf_program_deserialize_attachment(v, fds, &p); + if (r < 0) + return r; + + r = set_ensure_consume(bpfsetp, &bpf_program_hash_ops, p); + if (r < 0) + return r; + + return 0; +} |