1 files changed, 256 insertions, 0 deletions
diff --git a/src/shared/bpf-program.c b/src/shared/bpf-program.c
new file mode 100644
index 0000000..1023914
--- /dev/null
+++ b/src/shared/bpf-program.c
@@ -0,0 +1,256 @@
+/* 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 "fd-util.h"
+#include "memory-util.h"
+#include "missing_syscall.h"
+#include "path-util.h"
+
+int bpf_program_new(uint32_t prog_type, BPFProgram **ret) {
+        _cleanup_(bpf_program_unrefp) BPFProgram *p = NULL;
+
+        p = new0(BPFProgram, 1);
+        if (!p)
+                return -ENOMEM;
+
+        p->n_ref = 1;
+        p->prog_type = prog_type;
+        p->kernel_fd = -1;
+
+        *ret = TAKE_PTR(p);
+
+        return 0;
+}
+
+static BPFProgram *bpf_program_free(BPFProgram *p) {
+        assert(p);
+
+        /* 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 programs 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->instructions);
+        free(p->attached_path);
+
+        return mfree(p);
+}
+
+DEFINE_TRIVIAL_REF_UNREF_FUNC(BPFProgram, bpf_program, bpf_program_free);
+
+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->allocated, 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;
+
+        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 = -1;
+        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 = -1;
+
+        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(enum bpf_map_type type, size_t key_size, size_t value_size, size_t max_entries, uint32_t flags) {
+        union bpf_attr attr;
+        int fd;
+
+        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;
+
+        fd = bpf(BPF_MAP_CREATE, &attr, sizeof(attr));
+        if (fd < 0)
+                return -errno;
+
+        return fd;
+}
+
+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);
+
+        if (bpf(BPF_MAP_UPDATE_ELEM, &attr, sizeof(attr)) < 0)
+                return -errno;
+
+        return 0;
+}
+
+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);
+
+        if (bpf(BPF_MAP_LOOKUP_ELEM, &attr, sizeof(attr)) < 0)
+                return -errno;
+
+        return 0;
+}