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![Alexei Starovoitov](/assets/img/avatar_default.png)
If BPF_F_ALLOW_OVERRIDE flag is used in BPF_PROG_ATTACH command
to the given cgroup the descendent cgroup will be able to override
effective bpf program that was inherited from this cgroup.
By default it's not passed, therefore override is disallowed.
Examples:
1.
prog X attached to /A with default
prog Y fails to attach to /A/B and /A/B/C
Everything under /A runs prog X
2.
prog X attached to /A with allow_override.
prog Y fails to attach to /A/B with default (non-override)
prog M attached to /A/B with allow_override.
Everything under /A/B runs prog M only.
3.
prog X attached to /A with allow_override.
prog Y fails to attach to /A with default.
The user has to detach first to switch the mode.
In the future this behavior may be extended with a chain of
non-overridable programs.
Also fix the bug where detach from cgroup where nothing is attached
was not throwing error. Return ENOENT in such case.
Add several testcases and adjust libbpf.
Fixes: 3007098494
("cgroup: add support for eBPF programs")
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Acked-by: Daniel Borkmann <daniel@iogearbox.net>
Acked-by: Tejun Heo <tj@kernel.org>
Acked-by: Daniel Mack <daniel@zonque.org>
Signed-off-by: David S. Miller <davem@davemloft.net>
171 lines
4.6 KiB
C
171 lines
4.6 KiB
C
/* eBPF example program:
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*
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* - Creates arraymap in kernel with 4 bytes keys and 8 byte values
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*
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* - Loads eBPF program
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*
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* The eBPF program accesses the map passed in to store two pieces of
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* information. The number of invocations of the program, which maps
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* to the number of packets received, is stored to key 0. Key 1 is
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* incremented on each iteration by the number of bytes stored in
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* the skb.
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*
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* - Attaches the new program to a cgroup using BPF_PROG_ATTACH
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*
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* - Every second, reads map[0] and map[1] to see how many bytes and
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* packets were seen on any socket of tasks in the given cgroup.
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*/
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#define _GNU_SOURCE
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#include <stdio.h>
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#include <stdlib.h>
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#include <stddef.h>
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#include <string.h>
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#include <unistd.h>
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#include <assert.h>
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#include <errno.h>
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#include <fcntl.h>
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#include <linux/bpf.h>
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#include "libbpf.h"
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enum {
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MAP_KEY_PACKETS,
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MAP_KEY_BYTES,
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};
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char bpf_log_buf[BPF_LOG_BUF_SIZE];
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static int prog_load(int map_fd, int verdict)
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{
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struct bpf_insn prog[] = {
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BPF_MOV64_REG(BPF_REG_6, BPF_REG_1), /* save r6 so it's not clobbered by BPF_CALL */
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/* Count packets */
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BPF_MOV64_IMM(BPF_REG_0, MAP_KEY_PACKETS), /* r0 = 0 */
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BPF_STX_MEM(BPF_W, BPF_REG_10, BPF_REG_0, -4), /* *(u32 *)(fp - 4) = r0 */
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BPF_MOV64_REG(BPF_REG_2, BPF_REG_10),
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BPF_ALU64_IMM(BPF_ADD, BPF_REG_2, -4), /* r2 = fp - 4 */
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BPF_LD_MAP_FD(BPF_REG_1, map_fd), /* load map fd to r1 */
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BPF_RAW_INSN(BPF_JMP | BPF_CALL, 0, 0, 0, BPF_FUNC_map_lookup_elem),
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BPF_JMP_IMM(BPF_JEQ, BPF_REG_0, 0, 2),
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BPF_MOV64_IMM(BPF_REG_1, 1), /* r1 = 1 */
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BPF_RAW_INSN(BPF_STX | BPF_XADD | BPF_DW, BPF_REG_0, BPF_REG_1, 0, 0), /* xadd r0 += r1 */
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/* Count bytes */
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BPF_MOV64_IMM(BPF_REG_0, MAP_KEY_BYTES), /* r0 = 1 */
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BPF_STX_MEM(BPF_W, BPF_REG_10, BPF_REG_0, -4), /* *(u32 *)(fp - 4) = r0 */
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BPF_MOV64_REG(BPF_REG_2, BPF_REG_10),
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BPF_ALU64_IMM(BPF_ADD, BPF_REG_2, -4), /* r2 = fp - 4 */
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BPF_LD_MAP_FD(BPF_REG_1, map_fd),
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BPF_RAW_INSN(BPF_JMP | BPF_CALL, 0, 0, 0, BPF_FUNC_map_lookup_elem),
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BPF_JMP_IMM(BPF_JEQ, BPF_REG_0, 0, 2),
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BPF_LDX_MEM(BPF_W, BPF_REG_1, BPF_REG_6, offsetof(struct __sk_buff, len)), /* r1 = skb->len */
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BPF_RAW_INSN(BPF_STX | BPF_XADD | BPF_DW, BPF_REG_0, BPF_REG_1, 0, 0), /* xadd r0 += r1 */
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BPF_MOV64_IMM(BPF_REG_0, verdict), /* r0 = verdict */
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BPF_EXIT_INSN(),
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};
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size_t insns_cnt = sizeof(prog) / sizeof(struct bpf_insn);
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return bpf_load_program(BPF_PROG_TYPE_CGROUP_SKB,
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prog, insns_cnt, "GPL", 0,
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bpf_log_buf, BPF_LOG_BUF_SIZE);
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}
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static int usage(const char *argv0)
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{
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printf("Usage: %s [-d] [-D] <cg-path> <egress|ingress>\n", argv0);
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printf(" -d Drop Traffic\n");
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printf(" -D Detach filter, and exit\n");
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return EXIT_FAILURE;
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}
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static int attach_filter(int cg_fd, int type, int verdict)
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{
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int prog_fd, map_fd, ret, key;
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long long pkt_cnt, byte_cnt;
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map_fd = bpf_create_map(BPF_MAP_TYPE_ARRAY,
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sizeof(key), sizeof(byte_cnt),
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256, 0);
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if (map_fd < 0) {
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printf("Failed to create map: '%s'\n", strerror(errno));
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return EXIT_FAILURE;
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}
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prog_fd = prog_load(map_fd, verdict);
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printf("Output from kernel verifier:\n%s\n-------\n", bpf_log_buf);
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if (prog_fd < 0) {
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printf("Failed to load prog: '%s'\n", strerror(errno));
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return EXIT_FAILURE;
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}
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ret = bpf_prog_attach(prog_fd, cg_fd, type, 0);
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if (ret < 0) {
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printf("Failed to attach prog to cgroup: '%s'\n",
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strerror(errno));
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return EXIT_FAILURE;
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}
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while (1) {
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key = MAP_KEY_PACKETS;
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assert(bpf_map_lookup_elem(map_fd, &key, &pkt_cnt) == 0);
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key = MAP_KEY_BYTES;
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assert(bpf_map_lookup_elem(map_fd, &key, &byte_cnt) == 0);
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printf("cgroup received %lld packets, %lld bytes\n",
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pkt_cnt, byte_cnt);
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sleep(1);
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}
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return EXIT_SUCCESS;
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}
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int main(int argc, char **argv)
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{
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int detach_only = 0, verdict = 1;
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enum bpf_attach_type type;
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int opt, cg_fd, ret;
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while ((opt = getopt(argc, argv, "Dd")) != -1) {
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switch (opt) {
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case 'd':
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verdict = 0;
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break;
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case 'D':
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detach_only = 1;
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break;
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default:
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return usage(argv[0]);
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}
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}
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if (argc - optind < 2)
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return usage(argv[0]);
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if (strcmp(argv[optind + 1], "ingress") == 0)
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type = BPF_CGROUP_INET_INGRESS;
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else if (strcmp(argv[optind + 1], "egress") == 0)
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type = BPF_CGROUP_INET_EGRESS;
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else
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return usage(argv[0]);
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cg_fd = open(argv[optind], O_DIRECTORY | O_RDONLY);
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if (cg_fd < 0) {
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printf("Failed to open cgroup path: '%s'\n", strerror(errno));
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return EXIT_FAILURE;
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}
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if (detach_only) {
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ret = bpf_prog_detach(cg_fd, type);
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printf("bpf_prog_detach() returned '%s' (%d)\n",
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strerror(errno), errno);
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} else
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ret = attach_filter(cg_fd, type, verdict);
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return ret;
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}
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