// SPDX-License-Identifier: GPL-2.0
/*
 * Copyright (c) 2020 Facebook
 * Copyright 2020 Google LLC.
 */

#include <linux/pid.h>
#include <linux/sched.h>
#include <linux/rculist.h>
#include <linux/list.h>
#include <linux/hash.h>
#include <linux/types.h>
#include <linux/spinlock.h>
#include <linux/bpf.h>
#include <linux/bpf_local_storage.h>
#include <linux/filter.h>
#include <uapi/linux/btf.h>
#include <linux/btf_ids.h>
#include <linux/fdtable.h>

DEFINE_BPF_STORAGE_CACHE(task_cache);

static DEFINE_PER_CPU(int, bpf_task_storage_busy);

static void bpf_task_storage_lock(void)
{
        migrate_disable();
        __this_cpu_inc(bpf_task_storage_busy);
}

static void bpf_task_storage_unlock(void)
{
        __this_cpu_dec(bpf_task_storage_busy);
        migrate_enable();
}

static bool bpf_task_storage_trylock(void)
{
        migrate_disable();
        if (unlikely(__this_cpu_inc_return(bpf_task_storage_busy) != 1)) {
                __this_cpu_dec(bpf_task_storage_busy);
                migrate_enable();
                return false;
        }
        return true;
}

static struct bpf_local_storage __rcu **task_storage_ptr(void *owner)
{
        struct task_struct *task = owner;

        return &task->bpf_storage;
}

static struct bpf_local_storage_data *
task_storage_lookup(struct task_struct *task, struct bpf_map *map,
                    bool cacheit_lockit)
{
        struct bpf_local_storage *task_storage;
        struct bpf_local_storage_map *smap;

        task_storage = rcu_dereference(task->bpf_storage);
        if (!task_storage)
                return NULL;

        smap = (struct bpf_local_storage_map *)map;
        return bpf_local_storage_lookup(task_storage, smap, cacheit_lockit);
}

void bpf_task_storage_free(struct task_struct *task)
{
        struct bpf_local_storage_elem *selem;
        struct bpf_local_storage *local_storage;
        bool free_task_storage = false;
        struct hlist_node *n;
        unsigned long flags;

        rcu_read_lock();

        local_storage = rcu_dereference(task->bpf_storage);
        if (!local_storage) {
                rcu_read_unlock();
                return;
        }

        /* Neither the bpf_prog nor the bpf-map's syscall
         * could be modifying the local_storage->list now.
         * Thus, no elem can be added-to or deleted-from the
         * local_storage->list by the bpf_prog or by the bpf-map's syscall.
         *
         * It is racing with bpf_local_storage_map_free() alone
         * when unlinking elem from the local_storage->list and
         * the map's bucket->list.
         */
        bpf_task_storage_lock();
        raw_spin_lock_irqsave(&local_storage->lock, flags);
        hlist_for_each_entry_safe(selem, n, &local_storage->list, snode) {
                /* Always unlink from map before unlinking from
                 * local_storage.
                 */
                bpf_selem_unlink_map(selem);
                free_task_storage = bpf_selem_unlink_storage_nolock(
                        local_storage, selem, false);
        }
        raw_spin_unlock_irqrestore(&local_storage->lock, flags);
        bpf_task_storage_unlock();
        rcu_read_unlock();

        /* free_task_storage should always be true as long as
         * local_storage->list was non-empty.
         */
        if (free_task_storage)
                kfree_rcu(local_storage, rcu);
}

static void *bpf_pid_task_storage_lookup_elem(struct bpf_map *map, void *key)
{
        struct bpf_local_storage_data *sdata;
        struct task_struct *task;
        unsigned int f_flags;
        struct pid *pid;
        int fd, err;

        fd = *(int *)key;
        pid = pidfd_get_pid(fd, &f_flags);
        if (IS_ERR(pid))
                return ERR_CAST(pid);

        /* We should be in an RCU read side critical section, it should be safe
         * to call pid_task.
         */
        WARN_ON_ONCE(!rcu_read_lock_held());
        task = pid_task(pid, PIDTYPE_PID);
        if (!task) {
                err = -ENOENT;
                goto out;
        }

        bpf_task_storage_lock();
        sdata = task_storage_lookup(task, map, true);
        bpf_task_storage_unlock();
        put_pid(pid);
        return sdata ? sdata->data : NULL;
out:
        put_pid(pid);
        return ERR_PTR(err);
}

static int bpf_pid_task_storage_update_elem(struct bpf_map *map, void *key,
                                            void *value, u64 map_flags)
{
        struct bpf_local_storage_data *sdata;
        struct task_struct *task;
        unsigned int f_flags;
        struct pid *pid;
        int fd, err;

        fd = *(int *)key;
        pid = pidfd_get_pid(fd, &f_flags);
        if (IS_ERR(pid))
                return PTR_ERR(pid);

        /* We should be in an RCU read side critical section, it should be safe
         * to call pid_task.
         */
        WARN_ON_ONCE(!rcu_read_lock_held());
        task = pid_task(pid, PIDTYPE_PID);
        if (!task) {
                err = -ENOENT;
                goto out;
        }

        bpf_task_storage_lock();
        sdata = bpf_local_storage_update(
                task, (struct bpf_local_storage_map *)map, value, map_flags);
        bpf_task_storage_unlock();

        err = PTR_ERR_OR_ZERO(sdata);
out:
        put_pid(pid);
        return err;
}

static int task_storage_delete(struct task_struct *task, struct bpf_map *map)
{
        struct bpf_local_storage_data *sdata;

        sdata = task_storage_lookup(task, map, false);
        if (!sdata)
                return -ENOENT;

        bpf_selem_unlink(SELEM(sdata));

        return 0;
}

static int bpf_pid_task_storage_delete_elem(struct bpf_map *map, void *key)
{
        struct task_struct *task;
        unsigned int f_flags;
        struct pid *pid;
        int fd, err;

        fd = *(int *)key;
        pid = pidfd_get_pid(fd, &f_flags);
        if (IS_ERR(pid))
                return PTR_ERR(pid);

        /* We should be in an RCU read side critical section, it should be safe
         * to call pid_task.
         */
        WARN_ON_ONCE(!rcu_read_lock_held());
        task = pid_task(pid, PIDTYPE_PID);
        if (!task) {
                err = -ENOENT;
                goto out;
        }

        bpf_task_storage_lock();
        err = task_storage_delete(task, map);
        bpf_task_storage_unlock();
out:
        put_pid(pid);
        return err;
}

BPF_CALL_4(bpf_task_storage_get, struct bpf_map *, map, struct task_struct *,
           task, void *, value, u64, flags)
{
        struct bpf_local_storage_data *sdata;

        if (flags & ~(BPF_LOCAL_STORAGE_GET_F_CREATE))
                return (unsigned long)NULL;

        if (!task)
                return (unsigned long)NULL;

        if (!bpf_task_storage_trylock())
                return (unsigned long)NULL;

        sdata = task_storage_lookup(task, map, true);
        if (sdata)
                goto unlock;

        /* only allocate new storage, when the task is refcounted */
        if (refcount_read(&task->usage) &&
            (flags & BPF_LOCAL_STORAGE_GET_F_CREATE))
                sdata = bpf_local_storage_update(
                        task, (struct bpf_local_storage_map *)map, value,
                        BPF_NOEXIST);

unlock:
        bpf_task_storage_unlock();
        return IS_ERR_OR_NULL(sdata) ? (unsigned long)NULL :
                (unsigned long)sdata->data;
}

BPF_CALL_2(bpf_task_storage_delete, struct bpf_map *, map, struct task_struct *,
           task)
{
        int ret;

        if (!task)
                return -EINVAL;

        if (!bpf_task_storage_trylock())
                return -EBUSY;

        /* This helper must only be called from places where the lifetime of the task
         * is guaranteed. Either by being refcounted or by being protected
         * by an RCU read-side critical section.
         */
        ret = task_storage_delete(task, map);
        bpf_task_storage_unlock();
        return ret;
}

static int notsupp_get_next_key(struct bpf_map *map, void *key, void *next_key)
{
        return -ENOTSUPP;
}

static struct bpf_map *task_storage_map_alloc(union bpf_attr *attr)
{
        struct bpf_local_storage_map *smap;

        smap = bpf_local_storage_map_alloc(attr);
        if (IS_ERR(smap))
                return ERR_CAST(smap);

        smap->cache_idx = bpf_local_storage_cache_idx_get(&task_cache);
        return &smap->map;
}

static void task_storage_map_free(struct bpf_map *map)
{
        struct bpf_local_storage_map *smap;

        smap = (struct bpf_local_storage_map *)map;
        bpf_local_storage_cache_idx_free(&task_cache, smap->cache_idx);
        bpf_local_storage_map_free(smap, &bpf_task_storage_busy);
}

static int task_storage_map_btf_id;
const struct bpf_map_ops task_storage_map_ops = {
        .map_meta_equal = bpf_map_meta_equal,
        .map_alloc_check = bpf_local_storage_map_alloc_check,
        .map_alloc = task_storage_map_alloc,
        .map_free = task_storage_map_free,
        .map_get_next_key = notsupp_get_next_key,
        .map_lookup_elem = bpf_pid_task_storage_lookup_elem,
        .map_update_elem = bpf_pid_task_storage_update_elem,
        .map_delete_elem = bpf_pid_task_storage_delete_elem,
        .map_check_btf = bpf_local_storage_map_check_btf,
        .map_btf_name = "bpf_local_storage_map",
        .map_btf_id = &task_storage_map_btf_id,
        .map_owner_storage_ptr = task_storage_ptr,
};

const struct bpf_func_proto bpf_task_storage_get_proto = {
        .func = bpf_task_storage_get,
        .gpl_only = false,
        .ret_type = RET_PTR_TO_MAP_VALUE_OR_NULL,
        .arg1_type = ARG_CONST_MAP_PTR,
        .arg2_type = ARG_PTR_TO_BTF_ID,
        .arg2_btf_id = &btf_task_struct_ids[0],
        .arg3_type = ARG_PTR_TO_MAP_VALUE_OR_NULL,
        .arg4_type = ARG_ANYTHING,
};

const struct bpf_func_proto bpf_task_storage_delete_proto = {
        .func = bpf_task_storage_delete,
        .gpl_only = false,
        .ret_type = RET_INTEGER,
        .arg1_type = ARG_CONST_MAP_PTR,
        .arg2_type = ARG_PTR_TO_BTF_ID,
        .arg2_btf_id = &btf_task_struct_ids[0],
};