aa2b6f1d2b
So, the kernel's management of cgroup/BPF programs is a bit misdesigned: if you attach a BPF program to a cgroup and close the fd for it it will stay pinned to the cgroup with no chance of ever removing it again (or otherwise getting ahold of it again), because the fd is used for selecting which BPF program to detach. The only way to get rid of the program again is to destroy the cgroup itself. This is particularly bad for root the cgroup (and in fact any other cgroup that we cannot realistically remove during runtime, such as /system.slice, /init.scope or /system.slice/dbus.service) as getting rid of the program only works by rebooting the system. To counter this let's closely keep track to which cgroup a BPF program is attached and let's implicitly detach the BPF program when we are about to close the BPF fd. This hence changes the bpf_program_cgroup_attach() function to track where we attached the program and changes bpf_program_cgroup_detach() to use this information. Moreover bpf_program_unref() will now implicitly call bpf_program_cgroup_detach(). In order to simplify things, bpf_program_cgroup_attach() will now implicitly invoke bpf_program_load_kernel() when necessary, simplifying the caller's side. Finally, this adds proper reference counting to BPF programs. This is useful for working with two BPF programs in parallel: the BPF program we are preparing for installation and the BPF program we so far installed, shortening the window when we detach the old one and reattach the new one.
64 lines
2 KiB
C
64 lines
2 KiB
C
/* SPDX-License-Identifier: LGPL-2.1+ */
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#pragma once
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/***
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This file is part of systemd.
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Copyright 2016 Daniel Mack
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systemd is free software; you can redistribute it and/or modify it
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under the terms of the GNU Lesser General Public License as published by
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the Free Software Foundation; either version 2.1 of the License, or
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(at your option) any later version.
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systemd is distributed in the hope that it will be useful, but
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WITHOUT ANY WARRANTY; without even the implied warranty of
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MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
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Lesser General Public License for more details.
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You should have received a copy of the GNU Lesser General Public License
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along with systemd; If not, see <http://www.gnu.org/licenses/>.
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[Except for the stuff copy/pasted from the kernel sources, see below]
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***/
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#include <linux/bpf.h>
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#include <stdint.h>
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#include <sys/syscall.h>
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#include "list.h"
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#include "macro.h"
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typedef struct BPFProgram BPFProgram;
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struct BPFProgram {
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unsigned n_ref;
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int kernel_fd;
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uint32_t prog_type;
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size_t n_instructions;
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size_t allocated;
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struct bpf_insn *instructions;
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char *attached_path;
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int attached_type;
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uint32_t attached_flags;
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};
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int bpf_program_new(uint32_t prog_type, BPFProgram **ret);
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BPFProgram *bpf_program_unref(BPFProgram *p);
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BPFProgram *bpf_program_ref(BPFProgram *p);
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int bpf_program_add_instructions(BPFProgram *p, const struct bpf_insn *insn, size_t count);
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int bpf_program_load_kernel(BPFProgram *p, char *log_buf, size_t log_size);
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int bpf_program_cgroup_attach(BPFProgram *p, int type, const char *path, uint32_t flags);
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int bpf_program_cgroup_detach(BPFProgram *p);
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int bpf_map_new(enum bpf_map_type type, size_t key_size, size_t value_size, size_t max_entries, uint32_t flags);
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int bpf_map_update_element(int fd, const void *key, void *value);
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int bpf_map_lookup_element(int fd, const void *key, void *value);
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DEFINE_TRIVIAL_CLEANUP_FUNC(BPFProgram*, bpf_program_unref);
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