// 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 five 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.
 *  5. Walk the children of a given parent cgroup.
 *
 * 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;

        cgroup_lock();

        /* 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_CGROUP_ITER_DESCENDANTS_PRE)
                return css_next_descendant_pre(NULL, p->start_css);
        else if (p->order == BPF_CGROUP_ITER_DESCENDANTS_POST)
                return css_next_descendant_post(NULL, p->start_css);
        else if (p->order == BPF_CGROUP_ITER_CHILDREN)
                return css_next_child(NULL, p->start_css);
        else /* BPF_CGROUP_ITER_SELF_ONLY and BPF_CGROUP_ITER_ANCESTORS_UP */
                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;

        cgroup_unlock();

        /* 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_CGROUP_ITER_DESCENDANTS_PRE)
                return css_next_descendant_pre(curr, p->start_css);
        else if (p->order == BPF_CGROUP_ITER_DESCENDANTS_POST)
                return css_next_descendant_post(curr, p->start_css);
        else if (p->order == BPF_CGROUP_ITER_ANCESTORS_UP)
                return curr->parent;
        else if (p->order == BPF_CGROUP_ITER_CHILDREN)
                return css_next_child(curr, p->start_css);
        else  /* BPF_CGROUP_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_GLOBAL_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;

        /* bpf_iter_attach_cgroup() has already acquired an extra reference
         * for the start cgroup, but the reference may be released after
         * cgroup_iter_seq_init(), so acquire another reference for the
         * start cgroup.
         */
        p->start_css = &cgrp->self;
        css_get(p->start_css);
        p->terminate = false;
        p->visited_all = false;
        p->order = aux->cgroup.order;
        return 0;
}

static void cgroup_iter_seq_fini(void *priv)
{
        struct cgroup_iter_priv *p = (struct cgroup_iter_priv *)priv;

        css_put(p->start_css);
}

static const struct bpf_iter_seq_info cgroup_iter_seq_info = {
        .seq_ops                = &cgroup_iter_seq_ops,
        .init_seq_private       = cgroup_iter_seq_init,
        .fini_seq_private       = cgroup_iter_seq_fini,
        .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;

        switch (order) {
        case BPF_CGROUP_ITER_DESCENDANTS_PRE:
        case BPF_CGROUP_ITER_DESCENDANTS_POST:
        case BPF_CGROUP_ITER_ANCESTORS_UP:
        case BPF_CGROUP_ITER_SELF_ONLY:
        case BPF_CGROUP_ITER_CHILDREN:
                break;
        default:
                return -EINVAL;
        }

        if (fd && id)
                return -EINVAL;

        if (fd)
                cgrp = cgroup_v1v2_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_CGROUP_ITER_DESCENDANTS_PRE)
                seq_puts(seq, "order: descendants_pre\n");
        else if (aux->cgroup.order == BPF_CGROUP_ITER_DESCENDANTS_POST)
                seq_puts(seq, "order: descendants_post\n");
        else if (aux->cgroup.order == BPF_CGROUP_ITER_ANCESTORS_UP)
                seq_puts(seq, "order: ancestors_up\n");
        else if (aux->cgroup.order == BPF_CGROUP_ITER_CHILDREN)
                seq_puts(seq, "order: children\n");
        else /* BPF_CGROUP_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 | PTR_TRUSTED },
        },
        .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);

struct bpf_iter_css {
        __u64 __opaque[3];
} __attribute__((aligned(8)));

struct bpf_iter_css_kern {
        struct cgroup_subsys_state *start;
        struct cgroup_subsys_state *pos;
        unsigned int flags;
} __attribute__((aligned(8)));

__bpf_kfunc_start_defs();

__bpf_kfunc int bpf_iter_css_new(struct bpf_iter_css *it,
                struct cgroup_subsys_state *start, unsigned int flags)
{
        struct bpf_iter_css_kern *kit = (void *)it;

        BUILD_BUG_ON(sizeof(struct bpf_iter_css_kern) > sizeof(struct bpf_iter_css));
        BUILD_BUG_ON(__alignof__(struct bpf_iter_css_kern) != __alignof__(struct bpf_iter_css));

        kit->start = NULL;
        switch (flags) {
        case BPF_CGROUP_ITER_DESCENDANTS_PRE:
        case BPF_CGROUP_ITER_DESCENDANTS_POST:
        case BPF_CGROUP_ITER_ANCESTORS_UP:
        case BPF_CGROUP_ITER_CHILDREN:
                break;
        default:
                return -EINVAL;
        }

        kit->start = start;
        kit->pos = NULL;
        kit->flags = flags;
        return 0;
}

__bpf_kfunc struct cgroup_subsys_state *bpf_iter_css_next(struct bpf_iter_css *it)
{
        struct bpf_iter_css_kern *kit = (void *)it;

        if (!kit->start)
                return NULL;

        switch (kit->flags) {
        case BPF_CGROUP_ITER_DESCENDANTS_PRE:
                kit->pos = css_next_descendant_pre(kit->pos, kit->start);
                break;
        case BPF_CGROUP_ITER_DESCENDANTS_POST:
                kit->pos = css_next_descendant_post(kit->pos, kit->start);
                break;
        case BPF_CGROUP_ITER_CHILDREN:
                kit->pos = css_next_child(kit->pos, kit->start);
                break;
        case BPF_CGROUP_ITER_ANCESTORS_UP:
                kit->pos = kit->pos ? kit->pos->parent : kit->start;
        }

        return kit->pos;
}

__bpf_kfunc void bpf_iter_css_destroy(struct bpf_iter_css *it)
{
}

__bpf_kfunc_end_defs();