diff options
Diffstat (limited to 'src/basic/bpf-program.c')
| -rw-r--r-- | src/basic/bpf-program.c | 114 |
1 files changed, 100 insertions, 14 deletions
diff --git a/src/basic/bpf-program.c b/src/basic/bpf-program.c index 3690f812ae..a244742f91 100644 --- a/src/basic/bpf-program.c +++ b/src/basic/bpf-program.c @@ -28,6 +28,8 @@ #include "fd-util.h" #include "log.h" #include "missing.h" +#include "path-util.h" +#include "util.h" int bpf_program_new(uint32_t prog_type, BPFProgram **ret) { _cleanup_(bpf_program_unrefp) BPFProgram *p = NULL; @@ -36,6 +38,7 @@ int bpf_program_new(uint32_t prog_type, BPFProgram **ret) { if (!p) return log_oom(); + p->n_ref = 1; p->prog_type = prog_type; p->kernel_fd = -1; @@ -44,12 +47,39 @@ int bpf_program_new(uint32_t prog_type, BPFProgram **ret) { return 0; } +BPFProgram *bpf_program_ref(BPFProgram *p) { + if (!p) + return NULL; + + assert(p->n_ref > 0); + p->n_ref++; + + return p; +} + BPFProgram *bpf_program_unref(BPFProgram *p) { if (!p) return NULL; + assert(p->n_ref > 0); + p->n_ref--; + + if (p->n_ref > 0) + 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 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); } @@ -58,6 +88,9 @@ int bpf_program_add_instructions(BPFProgram *p, const struct bpf_insn *instructi 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; @@ -72,8 +105,10 @@ int bpf_program_load_kernel(BPFProgram *p, char *log_buf, size_t log_size) { assert(p); - if (p->kernel_fd >= 0) - return -EBUSY; + if (p->kernel_fd >= 0) { /* make this idempotent */ + memzero(log_buf, log_size); + return 0; + } attr = (union bpf_attr) { .prog_type = p->prog_type, @@ -93,13 +128,47 @@ int bpf_program_load_kernel(BPFProgram *p, char *log_buf, size_t log_size) { } 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; @@ -114,26 +183,43 @@ int bpf_program_cgroup_attach(BPFProgram *p, int type, const char *path, uint32_ 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(int type, const char *path) { +int bpf_program_cgroup_detach(BPFProgram *p) { _cleanup_close_ int fd = -1; - union bpf_attr attr; - assert(path); + assert(p); - fd = open(path, O_DIRECTORY|O_RDONLY|O_CLOEXEC); - if (fd < 0) - return -errno; + if (!p->attached_path) + return -EUNATCH; - attr = (union bpf_attr) { - .attach_type = type, - .target_fd = fd, - }; + fd = open(p->attached_path, O_DIRECTORY|O_RDONLY|O_CLOEXEC); + if (fd < 0) { + if (errno != ENOENT) + return -errno; - if (bpf(BPF_PROG_DETACH, &attr, sizeof(attr)) < 0) - 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; + + attr = (union bpf_attr) { + .attach_type = p->attached_type, + .target_fd = fd, + .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; } |