1// SPDX-License-Identifier: GPL-2.0-only
2/* Copyright (c) 2022 Google */
3#include <linux/bpf.h>
4#include <linux/btf_ids.h>
5#include <linux/cgroup.h>
6#include <linux/kernel.h>
7#include <linux/seq_file.h>
8
9#include "../cgroup/cgroup-internal.h" /* cgroup_mutex and cgroup_is_dead */
10
11/* cgroup_iter provides four modes of traversal to the cgroup hierarchy.
12 *
13 * 1. Walk the descendants of a cgroup in pre-order.
14 * 2. Walk the descendants of a cgroup in post-order.
15 * 3. Walk the ancestors of a cgroup.
16 * 4. Show the given cgroup only.
17 *
18 * For walking descendants, cgroup_iter can walk in either pre-order or
19 * post-order. For walking ancestors, the iter walks up from a cgroup to
20 * the root.
21 *
22 * The iter program can terminate the walk early by returning 1. Walk
23 * continues if prog returns 0.
24 *
25 * The prog can check (seq->num == 0) to determine whether this is
26 * the first element. The prog may also be passed a NULL cgroup,
27 * which means the walk has completed and the prog has a chance to
28 * do post-processing, such as outputting an epilogue.
29 *
30 * Note: the iter_prog is called with cgroup_mutex held.
31 *
32 * Currently only one session is supported, which means, depending on the
33 * volume of data bpf program intends to send to user space, the number
34 * of cgroups that can be walked is limited. For example, given the current
35 * buffer size is 8 * PAGE_SIZE, if the program sends 64B data for each
36 * cgroup, assuming PAGE_SIZE is 4kb, the total number of cgroups that can
37 * be walked is 512. This is a limitation of cgroup_iter. If the output data
38 * is larger than the kernel buffer size, after all data in the kernel buffer
39 * is consumed by user space, the subsequent read() syscall will signal
40 * EOPNOTSUPP. In order to work around, the user may have to update their
41 * program to reduce the volume of data sent to output. For example, skip
42 * some uninteresting cgroups.
43 */
44
45struct bpf_iter__cgroup {
46 __bpf_md_ptr(struct bpf_iter_meta *, meta);
47 __bpf_md_ptr(struct cgroup *, cgroup);
48};
49
50struct cgroup_iter_priv {
51 struct cgroup_subsys_state *start_css;
52 bool visited_all;
53 bool terminate;
54 int order;
55};
56
57static void *cgroup_iter_seq_start(struct seq_file *seq, loff_t *pos)
58{
59 struct cgroup_iter_priv *p = seq->private;
60
61 cgroup_lock();
62
63 /* cgroup_iter doesn't support read across multiple sessions. */
64 if (*pos > 0) {
65 if (p->visited_all)
66 return NULL;
67
68 /* Haven't visited all, but because cgroup_mutex has dropped,
69 * return -EOPNOTSUPP to indicate incomplete iteration.
70 */
71 return ERR_PTR(error: -EOPNOTSUPP);
72 }
73
74 ++*pos;
75 p->terminate = false;
76 p->visited_all = false;
77 if (p->order == BPF_CGROUP_ITER_DESCENDANTS_PRE)
78 return css_next_descendant_pre(NULL, css: p->start_css);
79 else if (p->order == BPF_CGROUP_ITER_DESCENDANTS_POST)
80 return css_next_descendant_post(NULL, css: p->start_css);
81 else /* BPF_CGROUP_ITER_SELF_ONLY and BPF_CGROUP_ITER_ANCESTORS_UP */
82 return p->start_css;
83}
84
85static int __cgroup_iter_seq_show(struct seq_file *seq,
86 struct cgroup_subsys_state *css, int in_stop);
87
88static void cgroup_iter_seq_stop(struct seq_file *seq, void *v)
89{
90 struct cgroup_iter_priv *p = seq->private;
91
92 cgroup_unlock();
93
94 /* pass NULL to the prog for post-processing */
95 if (!v) {
96 __cgroup_iter_seq_show(seq, NULL, in_stop: true);
97 p->visited_all = true;
98 }
99}
100
101static void *cgroup_iter_seq_next(struct seq_file *seq, void *v, loff_t *pos)
102{
103 struct cgroup_subsys_state *curr = (struct cgroup_subsys_state *)v;
104 struct cgroup_iter_priv *p = seq->private;
105
106 ++*pos;
107 if (p->terminate)
108 return NULL;
109
110 if (p->order == BPF_CGROUP_ITER_DESCENDANTS_PRE)
111 return css_next_descendant_pre(pos: curr, css: p->start_css);
112 else if (p->order == BPF_CGROUP_ITER_DESCENDANTS_POST)
113 return css_next_descendant_post(pos: curr, css: p->start_css);
114 else if (p->order == BPF_CGROUP_ITER_ANCESTORS_UP)
115 return curr->parent;
116 else /* BPF_CGROUP_ITER_SELF_ONLY */
117 return NULL;
118}
119
120static int __cgroup_iter_seq_show(struct seq_file *seq,
121 struct cgroup_subsys_state *css, int in_stop)
122{
123 struct cgroup_iter_priv *p = seq->private;
124 struct bpf_iter__cgroup ctx;
125 struct bpf_iter_meta meta;
126 struct bpf_prog *prog;
127 int ret = 0;
128
129 /* cgroup is dead, skip this element */
130 if (css && cgroup_is_dead(cgrp: css->cgroup))
131 return 0;
132
133 ctx.meta = &meta;
134 ctx.cgroup = css ? css->cgroup : NULL;
135 meta.seq = seq;
136 prog = bpf_iter_get_info(meta: &meta, in_stop);
137 if (prog)
138 ret = bpf_iter_run_prog(prog, ctx: &ctx);
139
140 /* if prog returns > 0, terminate after this element. */
141 if (ret != 0)
142 p->terminate = true;
143
144 return 0;
145}
146
147static int cgroup_iter_seq_show(struct seq_file *seq, void *v)
148{
149 return __cgroup_iter_seq_show(seq, css: (struct cgroup_subsys_state *)v,
150 in_stop: false);
151}
152
153static const struct seq_operations cgroup_iter_seq_ops = {
154 .start = cgroup_iter_seq_start,
155 .next = cgroup_iter_seq_next,
156 .stop = cgroup_iter_seq_stop,
157 .show = cgroup_iter_seq_show,
158};
159
160BTF_ID_LIST_GLOBAL_SINGLE(bpf_cgroup_btf_id, struct, cgroup)
161
162static int cgroup_iter_seq_init(void *priv, struct bpf_iter_aux_info *aux)
163{
164 struct cgroup_iter_priv *p = (struct cgroup_iter_priv *)priv;
165 struct cgroup *cgrp = aux->cgroup.start;
166
167 /* bpf_iter_attach_cgroup() has already acquired an extra reference
168 * for the start cgroup, but the reference may be released after
169 * cgroup_iter_seq_init(), so acquire another reference for the
170 * start cgroup.
171 */
172 p->start_css = &cgrp->self;
173 css_get(css: p->start_css);
174 p->terminate = false;
175 p->visited_all = false;
176 p->order = aux->cgroup.order;
177 return 0;
178}
179
180static void cgroup_iter_seq_fini(void *priv)
181{
182 struct cgroup_iter_priv *p = (struct cgroup_iter_priv *)priv;
183
184 css_put(css: p->start_css);
185}
186
187static const struct bpf_iter_seq_info cgroup_iter_seq_info = {
188 .seq_ops = &cgroup_iter_seq_ops,
189 .init_seq_private = cgroup_iter_seq_init,
190 .fini_seq_private = cgroup_iter_seq_fini,
191 .seq_priv_size = sizeof(struct cgroup_iter_priv),
192};
193
194static int bpf_iter_attach_cgroup(struct bpf_prog *prog,
195 union bpf_iter_link_info *linfo,
196 struct bpf_iter_aux_info *aux)
197{
198 int fd = linfo->cgroup.cgroup_fd;
199 u64 id = linfo->cgroup.cgroup_id;
200 int order = linfo->cgroup.order;
201 struct cgroup *cgrp;
202
203 if (order != BPF_CGROUP_ITER_DESCENDANTS_PRE &&
204 order != BPF_CGROUP_ITER_DESCENDANTS_POST &&
205 order != BPF_CGROUP_ITER_ANCESTORS_UP &&
206 order != BPF_CGROUP_ITER_SELF_ONLY)
207 return -EINVAL;
208
209 if (fd && id)
210 return -EINVAL;
211
212 if (fd)
213 cgrp = cgroup_v1v2_get_from_fd(fd);
214 else if (id)
215 cgrp = cgroup_get_from_id(id);
216 else /* walk the entire hierarchy by default. */
217 cgrp = cgroup_get_from_path(path: "/");
218
219 if (IS_ERR(ptr: cgrp))
220 return PTR_ERR(ptr: cgrp);
221
222 aux->cgroup.start = cgrp;
223 aux->cgroup.order = order;
224 return 0;
225}
226
227static void bpf_iter_detach_cgroup(struct bpf_iter_aux_info *aux)
228{
229 cgroup_put(cgrp: aux->cgroup.start);
230}
231
232static void bpf_iter_cgroup_show_fdinfo(const struct bpf_iter_aux_info *aux,
233 struct seq_file *seq)
234{
235 char *buf;
236
237 buf = kzalloc(PATH_MAX, GFP_KERNEL);
238 if (!buf) {
239 seq_puts(m: seq, s: "cgroup_path:\t<unknown>\n");
240 goto show_order;
241 }
242
243 /* If cgroup_path_ns() fails, buf will be an empty string, cgroup_path
244 * will print nothing.
245 *
246 * Path is in the calling process's cgroup namespace.
247 */
248 cgroup_path_ns(cgrp: aux->cgroup.start, buf, PATH_MAX,
249 current->nsproxy->cgroup_ns);
250 seq_printf(m: seq, fmt: "cgroup_path:\t%s\n", buf);
251 kfree(objp: buf);
252
253show_order:
254 if (aux->cgroup.order == BPF_CGROUP_ITER_DESCENDANTS_PRE)
255 seq_puts(m: seq, s: "order: descendants_pre\n");
256 else if (aux->cgroup.order == BPF_CGROUP_ITER_DESCENDANTS_POST)
257 seq_puts(m: seq, s: "order: descendants_post\n");
258 else if (aux->cgroup.order == BPF_CGROUP_ITER_ANCESTORS_UP)
259 seq_puts(m: seq, s: "order: ancestors_up\n");
260 else /* BPF_CGROUP_ITER_SELF_ONLY */
261 seq_puts(m: seq, s: "order: self_only\n");
262}
263
264static int bpf_iter_cgroup_fill_link_info(const struct bpf_iter_aux_info *aux,
265 struct bpf_link_info *info)
266{
267 info->iter.cgroup.order = aux->cgroup.order;
268 info->iter.cgroup.cgroup_id = cgroup_id(cgrp: aux->cgroup.start);
269 return 0;
270}
271
272DEFINE_BPF_ITER_FUNC(cgroup, struct bpf_iter_meta *meta,
273 struct cgroup *cgroup)
274
275static struct bpf_iter_reg bpf_cgroup_reg_info = {
276 .target = "cgroup",
277 .feature = BPF_ITER_RESCHED,
278 .attach_target = bpf_iter_attach_cgroup,
279 .detach_target = bpf_iter_detach_cgroup,
280 .show_fdinfo = bpf_iter_cgroup_show_fdinfo,
281 .fill_link_info = bpf_iter_cgroup_fill_link_info,
282 .ctx_arg_info_size = 1,
283 .ctx_arg_info = {
284 { offsetof(struct bpf_iter__cgroup, cgroup),
285 PTR_TO_BTF_ID_OR_NULL | PTR_TRUSTED },
286 },
287 .seq_info = &cgroup_iter_seq_info,
288};
289
290static int __init bpf_cgroup_iter_init(void)
291{
292 bpf_cgroup_reg_info.ctx_arg_info[0].btf_id = bpf_cgroup_btf_id[0];
293 return bpf_iter_reg_target(reg_info: &bpf_cgroup_reg_info);
294}
295
296late_initcall(bpf_cgroup_iter_init);
297
298struct bpf_iter_css {
299 __u64 __opaque[3];
300} __attribute__((aligned(8)));
301
302struct bpf_iter_css_kern {
303 struct cgroup_subsys_state *start;
304 struct cgroup_subsys_state *pos;
305 unsigned int flags;
306} __attribute__((aligned(8)));
307
308__bpf_kfunc_start_defs();
309
310__bpf_kfunc int bpf_iter_css_new(struct bpf_iter_css *it,
311 struct cgroup_subsys_state *start, unsigned int flags)
312{
313 struct bpf_iter_css_kern *kit = (void *)it;
314
315 BUILD_BUG_ON(sizeof(struct bpf_iter_css_kern) > sizeof(struct bpf_iter_css));
316 BUILD_BUG_ON(__alignof__(struct bpf_iter_css_kern) != __alignof__(struct bpf_iter_css));
317
318 kit->start = NULL;
319 switch (flags) {
320 case BPF_CGROUP_ITER_DESCENDANTS_PRE:
321 case BPF_CGROUP_ITER_DESCENDANTS_POST:
322 case BPF_CGROUP_ITER_ANCESTORS_UP:
323 break;
324 default:
325 return -EINVAL;
326 }
327
328 kit->start = start;
329 kit->pos = NULL;
330 kit->flags = flags;
331 return 0;
332}
333
334__bpf_kfunc struct cgroup_subsys_state *bpf_iter_css_next(struct bpf_iter_css *it)
335{
336 struct bpf_iter_css_kern *kit = (void *)it;
337
338 if (!kit->start)
339 return NULL;
340
341 switch (kit->flags) {
342 case BPF_CGROUP_ITER_DESCENDANTS_PRE:
343 kit->pos = css_next_descendant_pre(pos: kit->pos, css: kit->start);
344 break;
345 case BPF_CGROUP_ITER_DESCENDANTS_POST:
346 kit->pos = css_next_descendant_post(pos: kit->pos, css: kit->start);
347 break;
348 case BPF_CGROUP_ITER_ANCESTORS_UP:
349 kit->pos = kit->pos ? kit->pos->parent : kit->start;
350 }
351
352 return kit->pos;
353}
354
355__bpf_kfunc void bpf_iter_css_destroy(struct bpf_iter_css *it)
356{
357}
358
359__bpf_kfunc_end_defs();
360

source code of linux/kernel/bpf/cgroup_iter.c