--- /dev/null
+// SPDX-License-Identifier: GPL-2.0-only
+/* Copyright (c) 2022 Google */
+#include <linux/bpf.h>
+#include <linux/btf_ids.h>
+#include <linux/cgroup.h>
+#include <linux/kernel.h>
+#include <linux/seq_file.h>
+
+#include "../cgroup/cgroup-internal.h" /* cgroup_mutex and cgroup_is_dead */
+
+/* cgroup_iter provides four modes of traversal to the cgroup hierarchy.
+ *
+ * 1. Walk the descendants of a cgroup in pre-order.
+ * 2. Walk the descendants of a cgroup in post-order.
+ * 3. Walk the ancestors of a cgroup.
+ * 4. Show the given cgroup only.
+ *
+ * For walking descendants, cgroup_iter can walk in either pre-order or
+ * post-order. For walking ancestors, the iter walks up from a cgroup to
+ * the root.
+ *
+ * The iter program can terminate the walk early by returning 1. Walk
+ * continues if prog returns 0.
+ *
+ * The prog can check (seq->num == 0) to determine whether this is
+ * the first element. The prog may also be passed a NULL cgroup,
+ * which means the walk has completed and the prog has a chance to
+ * do post-processing, such as outputting an epilogue.
+ *
+ * Note: the iter_prog is called with cgroup_mutex held.
+ *
+ * Currently only one session is supported, which means, depending on the
+ * volume of data bpf program intends to send to user space, the number
+ * of cgroups that can be walked is limited. For example, given the current
+ * buffer size is 8 * PAGE_SIZE, if the program sends 64B data for each
+ * cgroup, assuming PAGE_SIZE is 4kb, the total number of cgroups that can
+ * be walked is 512. This is a limitation of cgroup_iter. If the output data
+ * is larger than the kernel buffer size, after all data in the kernel buffer
+ * is consumed by user space, the subsequent read() syscall will signal
+ * EOPNOTSUPP. In order to work around, the user may have to update their
+ * program to reduce the volume of data sent to output. For example, skip
+ * some uninteresting cgroups.
+ */
+
+struct bpf_iter__cgroup {
+ __bpf_md_ptr(struct bpf_iter_meta *, meta);
+ __bpf_md_ptr(struct cgroup *, cgroup);
+};
+
+struct cgroup_iter_priv {
+ struct cgroup_subsys_state *start_css;
+ bool visited_all;
+ bool terminate;
+ int order;
+};
+
+static void *cgroup_iter_seq_start(struct seq_file *seq, loff_t *pos)
+{
+ struct cgroup_iter_priv *p = seq->private;
+
+ mutex_lock(&cgroup_mutex);
+
+ /* cgroup_iter doesn't support read across multiple sessions. */
+ if (*pos > 0) {
+ if (p->visited_all)
+ return NULL;
+
+ /* Haven't visited all, but because cgroup_mutex has dropped,
+ * return -EOPNOTSUPP to indicate incomplete iteration.
+ */
+ return ERR_PTR(-EOPNOTSUPP);
+ }
+
+ ++*pos;
+ p->terminate = false;
+ p->visited_all = false;
+ if (p->order == BPF_ITER_DESCENDANTS_PRE)
+ return css_next_descendant_pre(NULL, p->start_css);
+ else if (p->order == BPF_ITER_DESCENDANTS_POST)
+ return css_next_descendant_post(NULL, p->start_css);
+ else if (p->order == BPF_ITER_ANCESTORS_UP)
+ return p->start_css;
+ else /* BPF_ITER_SELF_ONLY */
+ return p->start_css;
+}
+
+static int __cgroup_iter_seq_show(struct seq_file *seq,
+ struct cgroup_subsys_state *css, int in_stop);
+
+static void cgroup_iter_seq_stop(struct seq_file *seq, void *v)
+{
+ struct cgroup_iter_priv *p = seq->private;
+
+ mutex_unlock(&cgroup_mutex);
+
+ /* pass NULL to the prog for post-processing */
+ if (!v) {
+ __cgroup_iter_seq_show(seq, NULL, true);
+ p->visited_all = true;
+ }
+}
+
+static void *cgroup_iter_seq_next(struct seq_file *seq, void *v, loff_t *pos)
+{
+ struct cgroup_subsys_state *curr = (struct cgroup_subsys_state *)v;
+ struct cgroup_iter_priv *p = seq->private;
+
+ ++*pos;
+ if (p->terminate)
+ return NULL;
+
+ if (p->order == BPF_ITER_DESCENDANTS_PRE)
+ return css_next_descendant_pre(curr, p->start_css);
+ else if (p->order == BPF_ITER_DESCENDANTS_POST)
+ return css_next_descendant_post(curr, p->start_css);
+ else if (p->order == BPF_ITER_ANCESTORS_UP)
+ return curr->parent;
+ else /* BPF_ITER_SELF_ONLY */
+ return NULL;
+}
+
+static int __cgroup_iter_seq_show(struct seq_file *seq,
+ struct cgroup_subsys_state *css, int in_stop)
+{
+ struct cgroup_iter_priv *p = seq->private;
+ struct bpf_iter__cgroup ctx;
+ struct bpf_iter_meta meta;
+ struct bpf_prog *prog;
+ int ret = 0;
+
+ /* cgroup is dead, skip this element */
+ if (css && cgroup_is_dead(css->cgroup))
+ return 0;
+
+ ctx.meta = &meta;
+ ctx.cgroup = css ? css->cgroup : NULL;
+ meta.seq = seq;
+ prog = bpf_iter_get_info(&meta, in_stop);
+ if (prog)
+ ret = bpf_iter_run_prog(prog, &ctx);
+
+ /* if prog returns > 0, terminate after this element. */
+ if (ret != 0)
+ p->terminate = true;
+
+ return 0;
+}
+
+static int cgroup_iter_seq_show(struct seq_file *seq, void *v)
+{
+ return __cgroup_iter_seq_show(seq, (struct cgroup_subsys_state *)v,
+ false);
+}
+
+static const struct seq_operations cgroup_iter_seq_ops = {
+ .start = cgroup_iter_seq_start,
+ .next = cgroup_iter_seq_next,
+ .stop = cgroup_iter_seq_stop,
+ .show = cgroup_iter_seq_show,
+};
+
+BTF_ID_LIST_SINGLE(bpf_cgroup_btf_id, struct, cgroup)
+
+static int cgroup_iter_seq_init(void *priv, struct bpf_iter_aux_info *aux)
+{
+ struct cgroup_iter_priv *p = (struct cgroup_iter_priv *)priv;
+ struct cgroup *cgrp = aux->cgroup.start;
+
+ p->start_css = &cgrp->self;
+ p->terminate = false;
+ p->visited_all = false;
+ p->order = aux->cgroup.order;
+ return 0;
+}
+
+static const struct bpf_iter_seq_info cgroup_iter_seq_info = {
+ .seq_ops = &cgroup_iter_seq_ops,
+ .init_seq_private = cgroup_iter_seq_init,
+ .seq_priv_size = sizeof(struct cgroup_iter_priv),
+};
+
+static int bpf_iter_attach_cgroup(struct bpf_prog *prog,
+ union bpf_iter_link_info *linfo,
+ struct bpf_iter_aux_info *aux)
+{
+ int fd = linfo->cgroup.cgroup_fd;
+ u64 id = linfo->cgroup.cgroup_id;
+ int order = linfo->cgroup.order;
+ struct cgroup *cgrp;
+
+ if (order != BPF_ITER_DESCENDANTS_PRE &&
+ order != BPF_ITER_DESCENDANTS_POST &&
+ order != BPF_ITER_ANCESTORS_UP &&
+ order != BPF_ITER_SELF_ONLY)
+ return -EINVAL;
+
+ if (fd && id)
+ return -EINVAL;
+
+ if (fd)
+ cgrp = cgroup_get_from_fd(fd);
+ else if (id)
+ cgrp = cgroup_get_from_id(id);
+ else /* walk the entire hierarchy by default. */
+ cgrp = cgroup_get_from_path("/");
+
+ if (IS_ERR(cgrp))
+ return PTR_ERR(cgrp);
+
+ aux->cgroup.start = cgrp;
+ aux->cgroup.order = order;
+ return 0;
+}
+
+static void bpf_iter_detach_cgroup(struct bpf_iter_aux_info *aux)
+{
+ cgroup_put(aux->cgroup.start);
+}
+
+static void bpf_iter_cgroup_show_fdinfo(const struct bpf_iter_aux_info *aux,
+ struct seq_file *seq)
+{
+ char *buf;
+
+ buf = kzalloc(PATH_MAX, GFP_KERNEL);
+ if (!buf) {
+ seq_puts(seq, "cgroup_path:\t<unknown>\n");
+ goto show_order;
+ }
+
+ /* If cgroup_path_ns() fails, buf will be an empty string, cgroup_path
+ * will print nothing.
+ *
+ * Path is in the calling process's cgroup namespace.
+ */
+ cgroup_path_ns(aux->cgroup.start, buf, PATH_MAX,
+ current->nsproxy->cgroup_ns);
+ seq_printf(seq, "cgroup_path:\t%s\n", buf);
+ kfree(buf);
+
+show_order:
+ if (aux->cgroup.order == BPF_ITER_DESCENDANTS_PRE)
+ seq_puts(seq, "order: descendants_pre\n");
+ else if (aux->cgroup.order == BPF_ITER_DESCENDANTS_POST)
+ seq_puts(seq, "order: descendants_post\n");
+ else if (aux->cgroup.order == BPF_ITER_ANCESTORS_UP)
+ seq_puts(seq, "order: ancestors_up\n");
+ else /* BPF_ITER_SELF_ONLY */
+ seq_puts(seq, "order: self_only\n");
+}
+
+static int bpf_iter_cgroup_fill_link_info(const struct bpf_iter_aux_info *aux,
+ struct bpf_link_info *info)
+{
+ info->iter.cgroup.order = aux->cgroup.order;
+ info->iter.cgroup.cgroup_id = cgroup_id(aux->cgroup.start);
+ return 0;
+}
+
+DEFINE_BPF_ITER_FUNC(cgroup, struct bpf_iter_meta *meta,
+ struct cgroup *cgroup)
+
+static struct bpf_iter_reg bpf_cgroup_reg_info = {
+ .target = "cgroup",
+ .feature = BPF_ITER_RESCHED,
+ .attach_target = bpf_iter_attach_cgroup,
+ .detach_target = bpf_iter_detach_cgroup,
+ .show_fdinfo = bpf_iter_cgroup_show_fdinfo,
+ .fill_link_info = bpf_iter_cgroup_fill_link_info,
+ .ctx_arg_info_size = 1,
+ .ctx_arg_info = {
+ { offsetof(struct bpf_iter__cgroup, cgroup),
+ PTR_TO_BTF_ID_OR_NULL },
+ },
+ .seq_info = &cgroup_iter_seq_info,
+};
+
+static int __init bpf_cgroup_iter_init(void)
+{
+ bpf_cgroup_reg_info.ctx_arg_info[0].btf_id = bpf_cgroup_btf_id[0];
+ return bpf_iter_reg_target(&bpf_cgroup_reg_info);
+}
+
+late_initcall(bpf_cgroup_iter_init);
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