// SPDX-License-Identifier: GPL-2.0-only
/* Copyright (c) 2020 Facebook */

#include <linux/init.h>
#include <linux/namei.h>
#include <linux/pid_namespace.h>
#include <linux/fs.h>
#include <linux/fdtable.h>
#include <linux/filter.h>
#include <linux/btf_ids.h>

struct bpf_iter_seq_task_common {
        struct pid_namespace *ns;
};

struct bpf_iter_seq_task_info {
        /* The first field must be struct bpf_iter_seq_task_common.
         * this is assumed by {init, fini}_seq_pidns() callback functions.
         */
        struct bpf_iter_seq_task_common common;
        u32 tid;
};

static struct task_struct *task_seq_get_next(struct pid_namespace *ns,
                                             u32 *tid,
                                             bool skip_if_dup_files)
{
        struct task_struct *task = NULL;
        struct pid *pid;

        rcu_read_lock();
retry:
        pid = find_ge_pid(*tid, ns);
        if (pid) {
                *tid = pid_nr_ns(pid, ns);
                task = get_pid_task(pid, PIDTYPE_PID);
                if (!task) {
                        ++*tid;
                        goto retry;
                } else if (skip_if_dup_files && !thread_group_leader(task) &&
                           task->files == task->group_leader->files) {
                        put_task_struct(task);
                        task = NULL;
                        ++*tid;
                        goto retry;
                }
        }
        rcu_read_unlock();

        return task;
}

static void *task_seq_start(struct seq_file *seq, loff_t *pos)
{
        struct bpf_iter_seq_task_info *info = seq->private;
        struct task_struct *task;

        task = task_seq_get_next(info->common.ns, &info->tid, false);
        if (!task)
                return NULL;

        if (*pos == 0)
                ++*pos;
        return task;
}

static void *task_seq_next(struct seq_file *seq, void *v, loff_t *pos)
{
        struct bpf_iter_seq_task_info *info = seq->private;
        struct task_struct *task;

        ++*pos;
        ++info->tid;
        put_task_struct((struct task_struct *)v);
        task = task_seq_get_next(info->common.ns, &info->tid, false);
        if (!task)
                return NULL;

        return task;
}

struct bpf_iter__task {
        __bpf_md_ptr(struct bpf_iter_meta *, meta);
        __bpf_md_ptr(struct task_struct *, task);
};

DEFINE_BPF_ITER_FUNC(task, struct bpf_iter_meta *meta, struct task_struct *task)

static int __task_seq_show(struct seq_file *seq, struct task_struct *task,
                           bool in_stop)
{
        struct bpf_iter_meta meta;
        struct bpf_iter__task ctx;
        struct bpf_prog *prog;

        meta.seq = seq;
        prog = bpf_iter_get_info(&meta, in_stop);
        if (!prog)
                return 0;

        meta.seq = seq;
        ctx.meta = &meta;
        ctx.task = task;
        return bpf_iter_run_prog(prog, &ctx);
}

static int task_seq_show(struct seq_file *seq, void *v)
{
        return __task_seq_show(seq, v, false);
}

static void task_seq_stop(struct seq_file *seq, void *v)
{
        if (!v)
                (void)__task_seq_show(seq, v, true);
        else
                put_task_struct((struct task_struct *)v);
}

static const struct seq_operations task_seq_ops = {
        .start  = task_seq_start,
        .next   = task_seq_next,
        .stop   = task_seq_stop,
        .show   = task_seq_show,
};

struct bpf_iter_seq_task_file_info {
        /* The first field must be struct bpf_iter_seq_task_common.
         * this is assumed by {init, fini}_seq_pidns() callback functions.
         */
        struct bpf_iter_seq_task_common common;
        struct task_struct *task;
        u32 tid;
        u32 fd;
};

static struct file *
task_file_seq_get_next(struct bpf_iter_seq_task_file_info *info)
{
        struct pid_namespace *ns = info->common.ns;
        u32 curr_tid = info->tid;
        struct task_struct *curr_task;
        unsigned int curr_fd = info->fd;

        /* If this function returns a non-NULL file object,
         * it held a reference to the task/file.
         * Otherwise, it does not hold any reference.
         */
again:
        if (info->task) {
                curr_task = info->task;
                curr_fd = info->fd;
        } else {
                curr_task = task_seq_get_next(ns, &curr_tid, true);
                if (!curr_task) {
                        info->task = NULL;
                        info->tid = curr_tid;
                        return NULL;
                }

                /* set info->task and info->tid */
                info->task = curr_task;
                if (curr_tid == info->tid) {
                        curr_fd = info->fd;
                } else {
                        info->tid = curr_tid;
                        curr_fd = 0;
                }
        }

        rcu_read_lock();
        for (;; curr_fd++) {
                struct file *f;
                f = task_lookup_next_fd_rcu(curr_task, &curr_fd);
                if (!f)
                        break;
                if (!get_file_rcu(f))
                        continue;

                /* set info->fd */
                info->fd = curr_fd;
                rcu_read_unlock();
                return f;
        }

        /* the current task is done, go to the next task */
        rcu_read_unlock();
        put_task_struct(curr_task);
        info->task = NULL;
        info->fd = 0;
        curr_tid = ++(info->tid);
        goto again;
}

static void *task_file_seq_start(struct seq_file *seq, loff_t *pos)
{
        struct bpf_iter_seq_task_file_info *info = seq->private;
        struct file *file;

        info->task = NULL;
        file = task_file_seq_get_next(info);
        if (file && *pos == 0)
                ++*pos;

        return file;
}

static void *task_file_seq_next(struct seq_file *seq, void *v, loff_t *pos)
{
        struct bpf_iter_seq_task_file_info *info = seq->private;

        ++*pos;
        ++info->fd;
        fput((struct file *)v);
        return task_file_seq_get_next(info);
}

struct bpf_iter__task_file {
        __bpf_md_ptr(struct bpf_iter_meta *, meta);
        __bpf_md_ptr(struct task_struct *, task);
        u32 fd __aligned(8);
        __bpf_md_ptr(struct file *, file);
};

DEFINE_BPF_ITER_FUNC(task_file, struct bpf_iter_meta *meta,
                     struct task_struct *task, u32 fd,
                     struct file *file)

static int __task_file_seq_show(struct seq_file *seq, struct file *file,
                                bool in_stop)
{
        struct bpf_iter_seq_task_file_info *info = seq->private;
        struct bpf_iter__task_file ctx;
        struct bpf_iter_meta meta;
        struct bpf_prog *prog;

        meta.seq = seq;
        prog = bpf_iter_get_info(&meta, in_stop);
        if (!prog)
                return 0;

        ctx.meta = &meta;
        ctx.task = info->task;
        ctx.fd = info->fd;
        ctx.file = file;
        return bpf_iter_run_prog(prog, &ctx);
}

static int task_file_seq_show(struct seq_file *seq, void *v)
{
        return __task_file_seq_show(seq, v, false);
}

static void task_file_seq_stop(struct seq_file *seq, void *v)
{
        struct bpf_iter_seq_task_file_info *info = seq->private;

        if (!v) {
                (void)__task_file_seq_show(seq, v, true);
        } else {
                fput((struct file *)v);
                put_task_struct(info->task);
                info->task = NULL;
        }
}

static int init_seq_pidns(void *priv_data, struct bpf_iter_aux_info *aux)
{
        struct bpf_iter_seq_task_common *common = priv_data;

        common->ns = get_pid_ns(task_active_pid_ns(current));
        return 0;
}

static void fini_seq_pidns(void *priv_data)
{
        struct bpf_iter_seq_task_common *common = priv_data;

        put_pid_ns(common->ns);
}

static const struct seq_operations task_file_seq_ops = {
        .start  = task_file_seq_start,
        .next   = task_file_seq_next,
        .stop   = task_file_seq_stop,
        .show   = task_file_seq_show,
};

BTF_ID_LIST(btf_task_file_ids)
BTF_ID(struct, task_struct)
BTF_ID(struct, file)

static const struct bpf_iter_seq_info task_seq_info = {
        .seq_ops                = &task_seq_ops,
        .init_seq_private       = init_seq_pidns,
        .fini_seq_private       = fini_seq_pidns,
        .seq_priv_size          = sizeof(struct bpf_iter_seq_task_info),
};

static struct bpf_iter_reg task_reg_info = {
        .target                 = "task",
        .feature                = BPF_ITER_RESCHED,
        .ctx_arg_info_size      = 1,
        .ctx_arg_info           = {
                { offsetof(struct bpf_iter__task, task),
                  PTR_TO_BTF_ID_OR_NULL },
        },
        .seq_info               = &task_seq_info,
};

static const struct bpf_iter_seq_info task_file_seq_info = {
        .seq_ops                = &task_file_seq_ops,
        .init_seq_private       = init_seq_pidns,
        .fini_seq_private       = fini_seq_pidns,
        .seq_priv_size          = sizeof(struct bpf_iter_seq_task_file_info),
};

static struct bpf_iter_reg task_file_reg_info = {
        .target                 = "task_file",
        .feature                = BPF_ITER_RESCHED,
        .ctx_arg_info_size      = 2,
        .ctx_arg_info           = {
                { offsetof(struct bpf_iter__task_file, task),
                  PTR_TO_BTF_ID_OR_NULL },
                { offsetof(struct bpf_iter__task_file, file),
                  PTR_TO_BTF_ID_OR_NULL },
        },
        .seq_info               = &task_file_seq_info,
};

static int __init task_iter_init(void)
{
        int ret;

        task_reg_info.ctx_arg_info[0].btf_id = btf_task_file_ids[0];
        ret = bpf_iter_reg_target(&task_reg_info);
        if (ret)
                return ret;

        task_file_reg_info.ctx_arg_info[0].btf_id = btf_task_file_ids[0];
        task_file_reg_info.ctx_arg_info[1].btf_id = btf_task_file_ids[1];
        return bpf_iter_reg_target(&task_file_reg_info);
}
late_initcall(task_iter_init);