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![Chuyi Zhou](/assets/img/avatar_default.png)
BTF_TYPE_SAFE_TRUSTED(struct bpf_iter__task) in verifier.c wanted to
teach BPF verifier that bpf_iter__task -> task is a trusted ptr. But it
doesn't work well.
The reason is, bpf_iter__task -> task would go through btf_ctx_access()
which enforces the reg_type of 'task' is ctx_arg_info->reg_type, and in
task_iter.c, we actually explicitly declare that the
ctx_arg_info->reg_type is PTR_TO_BTF_ID_OR_NULL.
Actually we have a previous case like this[1] where PTR_TRUSTED is added to
the arg flag for map_iter.
This patch sets ctx_arg_info->reg_type is PTR_TO_BTF_ID_OR_NULL |
PTR_TRUSTED in task_reg_info.
Similarly, bpf_cgroup_reg_info -> cgroup is also PTR_TRUSTED since we are
under the protection of cgroup_mutex and we would check cgroup_is_dead()
in __cgroup_iter_seq_show().
This patch is to improve the user experience of the newly introduced
bpf_iter_css_task kfunc before hitting the mainline. The Fixes tag is
pointing to the commit introduced the bpf_iter_css_task kfunc.
Link[1]:https://lore.kernel.org/all/20230706133932.45883-3-aspsk@isovalent.com/
Fixes: 9c66dc94b6
("bpf: Introduce css_task open-coded iterator kfuncs")
Signed-off-by: Chuyi Zhou <zhouchuyi@bytedance.com>
Acked-by: Yonghong Song <yonghong.song@linux.dev>
Link: https://lore.kernel.org/r/20231107132204.912120-2-zhouchuyi@bytedance.com
Signed-off-by: Martin KaFai Lau <martin.lau@kernel.org>
360 lines
9.9 KiB
C
360 lines
9.9 KiB
C
// SPDX-License-Identifier: GPL-2.0-only
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/* Copyright (c) 2022 Google */
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#include <linux/bpf.h>
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#include <linux/btf_ids.h>
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#include <linux/cgroup.h>
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#include <linux/kernel.h>
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#include <linux/seq_file.h>
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#include "../cgroup/cgroup-internal.h" /* cgroup_mutex and cgroup_is_dead */
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/* cgroup_iter provides four modes of traversal to the cgroup hierarchy.
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*
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* 1. Walk the descendants of a cgroup in pre-order.
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* 2. Walk the descendants of a cgroup in post-order.
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* 3. Walk the ancestors of a cgroup.
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* 4. Show the given cgroup only.
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*
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* For walking descendants, cgroup_iter can walk in either pre-order or
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* post-order. For walking ancestors, the iter walks up from a cgroup to
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* the root.
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*
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* The iter program can terminate the walk early by returning 1. Walk
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* continues if prog returns 0.
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*
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* The prog can check (seq->num == 0) to determine whether this is
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* the first element. The prog may also be passed a NULL cgroup,
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* which means the walk has completed and the prog has a chance to
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* do post-processing, such as outputting an epilogue.
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*
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* Note: the iter_prog is called with cgroup_mutex held.
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*
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* Currently only one session is supported, which means, depending on the
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* volume of data bpf program intends to send to user space, the number
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* of cgroups that can be walked is limited. For example, given the current
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* buffer size is 8 * PAGE_SIZE, if the program sends 64B data for each
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* cgroup, assuming PAGE_SIZE is 4kb, the total number of cgroups that can
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* be walked is 512. This is a limitation of cgroup_iter. If the output data
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* is larger than the kernel buffer size, after all data in the kernel buffer
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* is consumed by user space, the subsequent read() syscall will signal
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* EOPNOTSUPP. In order to work around, the user may have to update their
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* program to reduce the volume of data sent to output. For example, skip
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* some uninteresting cgroups.
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*/
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struct bpf_iter__cgroup {
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__bpf_md_ptr(struct bpf_iter_meta *, meta);
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__bpf_md_ptr(struct cgroup *, cgroup);
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};
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struct cgroup_iter_priv {
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struct cgroup_subsys_state *start_css;
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bool visited_all;
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bool terminate;
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int order;
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};
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static void *cgroup_iter_seq_start(struct seq_file *seq, loff_t *pos)
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{
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struct cgroup_iter_priv *p = seq->private;
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cgroup_lock();
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/* cgroup_iter doesn't support read across multiple sessions. */
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if (*pos > 0) {
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if (p->visited_all)
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return NULL;
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/* Haven't visited all, but because cgroup_mutex has dropped,
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* return -EOPNOTSUPP to indicate incomplete iteration.
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*/
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return ERR_PTR(-EOPNOTSUPP);
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}
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++*pos;
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p->terminate = false;
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p->visited_all = false;
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if (p->order == BPF_CGROUP_ITER_DESCENDANTS_PRE)
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return css_next_descendant_pre(NULL, p->start_css);
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else if (p->order == BPF_CGROUP_ITER_DESCENDANTS_POST)
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return css_next_descendant_post(NULL, p->start_css);
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else /* BPF_CGROUP_ITER_SELF_ONLY and BPF_CGROUP_ITER_ANCESTORS_UP */
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return p->start_css;
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}
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static int __cgroup_iter_seq_show(struct seq_file *seq,
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struct cgroup_subsys_state *css, int in_stop);
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static void cgroup_iter_seq_stop(struct seq_file *seq, void *v)
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{
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struct cgroup_iter_priv *p = seq->private;
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cgroup_unlock();
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/* pass NULL to the prog for post-processing */
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if (!v) {
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__cgroup_iter_seq_show(seq, NULL, true);
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p->visited_all = true;
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}
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}
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static void *cgroup_iter_seq_next(struct seq_file *seq, void *v, loff_t *pos)
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{
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struct cgroup_subsys_state *curr = (struct cgroup_subsys_state *)v;
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struct cgroup_iter_priv *p = seq->private;
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++*pos;
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if (p->terminate)
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return NULL;
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if (p->order == BPF_CGROUP_ITER_DESCENDANTS_PRE)
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return css_next_descendant_pre(curr, p->start_css);
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else if (p->order == BPF_CGROUP_ITER_DESCENDANTS_POST)
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return css_next_descendant_post(curr, p->start_css);
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else if (p->order == BPF_CGROUP_ITER_ANCESTORS_UP)
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return curr->parent;
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else /* BPF_CGROUP_ITER_SELF_ONLY */
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return NULL;
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}
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static int __cgroup_iter_seq_show(struct seq_file *seq,
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struct cgroup_subsys_state *css, int in_stop)
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{
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struct cgroup_iter_priv *p = seq->private;
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struct bpf_iter__cgroup ctx;
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struct bpf_iter_meta meta;
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struct bpf_prog *prog;
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int ret = 0;
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/* cgroup is dead, skip this element */
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if (css && cgroup_is_dead(css->cgroup))
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return 0;
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ctx.meta = &meta;
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ctx.cgroup = css ? css->cgroup : NULL;
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meta.seq = seq;
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prog = bpf_iter_get_info(&meta, in_stop);
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if (prog)
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ret = bpf_iter_run_prog(prog, &ctx);
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/* if prog returns > 0, terminate after this element. */
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if (ret != 0)
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p->terminate = true;
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return 0;
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}
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static int cgroup_iter_seq_show(struct seq_file *seq, void *v)
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{
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return __cgroup_iter_seq_show(seq, (struct cgroup_subsys_state *)v,
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false);
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}
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static const struct seq_operations cgroup_iter_seq_ops = {
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.start = cgroup_iter_seq_start,
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.next = cgroup_iter_seq_next,
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.stop = cgroup_iter_seq_stop,
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.show = cgroup_iter_seq_show,
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};
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BTF_ID_LIST_GLOBAL_SINGLE(bpf_cgroup_btf_id, struct, cgroup)
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static int cgroup_iter_seq_init(void *priv, struct bpf_iter_aux_info *aux)
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{
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struct cgroup_iter_priv *p = (struct cgroup_iter_priv *)priv;
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struct cgroup *cgrp = aux->cgroup.start;
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/* bpf_iter_attach_cgroup() has already acquired an extra reference
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* for the start cgroup, but the reference may be released after
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* cgroup_iter_seq_init(), so acquire another reference for the
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* start cgroup.
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*/
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p->start_css = &cgrp->self;
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css_get(p->start_css);
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p->terminate = false;
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p->visited_all = false;
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p->order = aux->cgroup.order;
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return 0;
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}
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static void cgroup_iter_seq_fini(void *priv)
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{
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struct cgroup_iter_priv *p = (struct cgroup_iter_priv *)priv;
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css_put(p->start_css);
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}
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static const struct bpf_iter_seq_info cgroup_iter_seq_info = {
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.seq_ops = &cgroup_iter_seq_ops,
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.init_seq_private = cgroup_iter_seq_init,
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.fini_seq_private = cgroup_iter_seq_fini,
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.seq_priv_size = sizeof(struct cgroup_iter_priv),
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};
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static int bpf_iter_attach_cgroup(struct bpf_prog *prog,
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union bpf_iter_link_info *linfo,
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struct bpf_iter_aux_info *aux)
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{
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int fd = linfo->cgroup.cgroup_fd;
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u64 id = linfo->cgroup.cgroup_id;
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int order = linfo->cgroup.order;
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struct cgroup *cgrp;
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if (order != BPF_CGROUP_ITER_DESCENDANTS_PRE &&
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order != BPF_CGROUP_ITER_DESCENDANTS_POST &&
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order != BPF_CGROUP_ITER_ANCESTORS_UP &&
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order != BPF_CGROUP_ITER_SELF_ONLY)
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return -EINVAL;
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if (fd && id)
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return -EINVAL;
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if (fd)
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cgrp = cgroup_v1v2_get_from_fd(fd);
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else if (id)
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cgrp = cgroup_get_from_id(id);
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else /* walk the entire hierarchy by default. */
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cgrp = cgroup_get_from_path("/");
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if (IS_ERR(cgrp))
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return PTR_ERR(cgrp);
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aux->cgroup.start = cgrp;
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aux->cgroup.order = order;
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return 0;
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}
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static void bpf_iter_detach_cgroup(struct bpf_iter_aux_info *aux)
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{
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cgroup_put(aux->cgroup.start);
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}
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static void bpf_iter_cgroup_show_fdinfo(const struct bpf_iter_aux_info *aux,
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struct seq_file *seq)
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{
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char *buf;
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buf = kzalloc(PATH_MAX, GFP_KERNEL);
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if (!buf) {
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seq_puts(seq, "cgroup_path:\t<unknown>\n");
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goto show_order;
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}
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/* If cgroup_path_ns() fails, buf will be an empty string, cgroup_path
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* will print nothing.
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*
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* Path is in the calling process's cgroup namespace.
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*/
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cgroup_path_ns(aux->cgroup.start, buf, PATH_MAX,
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current->nsproxy->cgroup_ns);
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seq_printf(seq, "cgroup_path:\t%s\n", buf);
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kfree(buf);
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show_order:
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if (aux->cgroup.order == BPF_CGROUP_ITER_DESCENDANTS_PRE)
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seq_puts(seq, "order: descendants_pre\n");
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else if (aux->cgroup.order == BPF_CGROUP_ITER_DESCENDANTS_POST)
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seq_puts(seq, "order: descendants_post\n");
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else if (aux->cgroup.order == BPF_CGROUP_ITER_ANCESTORS_UP)
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seq_puts(seq, "order: ancestors_up\n");
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else /* BPF_CGROUP_ITER_SELF_ONLY */
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seq_puts(seq, "order: self_only\n");
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}
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static int bpf_iter_cgroup_fill_link_info(const struct bpf_iter_aux_info *aux,
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struct bpf_link_info *info)
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{
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info->iter.cgroup.order = aux->cgroup.order;
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info->iter.cgroup.cgroup_id = cgroup_id(aux->cgroup.start);
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return 0;
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}
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DEFINE_BPF_ITER_FUNC(cgroup, struct bpf_iter_meta *meta,
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struct cgroup *cgroup)
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static struct bpf_iter_reg bpf_cgroup_reg_info = {
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.target = "cgroup",
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.feature = BPF_ITER_RESCHED,
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.attach_target = bpf_iter_attach_cgroup,
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.detach_target = bpf_iter_detach_cgroup,
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.show_fdinfo = bpf_iter_cgroup_show_fdinfo,
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.fill_link_info = bpf_iter_cgroup_fill_link_info,
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.ctx_arg_info_size = 1,
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.ctx_arg_info = {
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{ offsetof(struct bpf_iter__cgroup, cgroup),
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PTR_TO_BTF_ID_OR_NULL | PTR_TRUSTED },
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},
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.seq_info = &cgroup_iter_seq_info,
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};
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static int __init bpf_cgroup_iter_init(void)
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{
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bpf_cgroup_reg_info.ctx_arg_info[0].btf_id = bpf_cgroup_btf_id[0];
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return bpf_iter_reg_target(&bpf_cgroup_reg_info);
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}
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late_initcall(bpf_cgroup_iter_init);
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struct bpf_iter_css {
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__u64 __opaque[3];
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} __attribute__((aligned(8)));
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struct bpf_iter_css_kern {
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struct cgroup_subsys_state *start;
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struct cgroup_subsys_state *pos;
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unsigned int flags;
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} __attribute__((aligned(8)));
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__bpf_kfunc_start_defs();
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__bpf_kfunc int bpf_iter_css_new(struct bpf_iter_css *it,
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struct cgroup_subsys_state *start, unsigned int flags)
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{
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struct bpf_iter_css_kern *kit = (void *)it;
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BUILD_BUG_ON(sizeof(struct bpf_iter_css_kern) > sizeof(struct bpf_iter_css));
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BUILD_BUG_ON(__alignof__(struct bpf_iter_css_kern) != __alignof__(struct bpf_iter_css));
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kit->start = NULL;
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switch (flags) {
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case BPF_CGROUP_ITER_DESCENDANTS_PRE:
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case BPF_CGROUP_ITER_DESCENDANTS_POST:
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case BPF_CGROUP_ITER_ANCESTORS_UP:
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break;
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default:
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return -EINVAL;
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}
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kit->start = start;
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kit->pos = NULL;
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kit->flags = flags;
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return 0;
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}
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__bpf_kfunc struct cgroup_subsys_state *bpf_iter_css_next(struct bpf_iter_css *it)
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{
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struct bpf_iter_css_kern *kit = (void *)it;
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if (!kit->start)
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return NULL;
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switch (kit->flags) {
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case BPF_CGROUP_ITER_DESCENDANTS_PRE:
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kit->pos = css_next_descendant_pre(kit->pos, kit->start);
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break;
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case BPF_CGROUP_ITER_DESCENDANTS_POST:
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kit->pos = css_next_descendant_post(kit->pos, kit->start);
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break;
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case BPF_CGROUP_ITER_ANCESTORS_UP:
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kit->pos = kit->pos ? kit->pos->parent : kit->start;
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}
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return kit->pos;
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}
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__bpf_kfunc void bpf_iter_css_destroy(struct bpf_iter_css *it)
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{
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}
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__bpf_kfunc_end_defs();
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