// SPDX-License-Identifier: GPL-2.0-only
/*
 * Minimal file system backend for holding eBPF maps and programs,
 * used by bpf(2) object pinning.
 *
 * Authors:
 *
 *      Daniel Borkmann <daniel@iogearbox.net>
 */

#include <linux/init.h>
#include <linux/magic.h>
#include <linux/major.h>
#include <linux/mount.h>
#include <linux/namei.h>
#include <linux/fs.h>
#include <linux/fs_context.h>
#include <linux/fs_parser.h>
#include <linux/kdev_t.h>
#include <linux/filter.h>
#include <linux/bpf.h>
#include <linux/bpf_trace.h>
#include <linux/kstrtox.h>
#include "preload/bpf_preload.h"

enum bpf_type {
        BPF_TYPE_UNSPEC = 0,
        BPF_TYPE_PROG,
        BPF_TYPE_MAP,
        BPF_TYPE_LINK,
};

static void *bpf_any_get(void *raw, enum bpf_type type)
{
        switch (type) {
        case BPF_TYPE_PROG:
                bpf_prog_inc(raw);
                break;
        case BPF_TYPE_MAP:
                bpf_map_inc_with_uref(raw);
                break;
        case BPF_TYPE_LINK:
                bpf_link_inc(raw);
                break;
        default:
                WARN_ON_ONCE(1);
                break;
        }

        return raw;
}

static void bpf_any_put(void *raw, enum bpf_type type)
{
        switch (type) {
        case BPF_TYPE_PROG:
                bpf_prog_put(raw);
                break;
        case BPF_TYPE_MAP:
                bpf_map_put_with_uref(raw);
                break;
        case BPF_TYPE_LINK:
                bpf_link_put(raw);
                break;
        default:
                WARN_ON_ONCE(1);
                break;
        }
}

static void *bpf_fd_probe_obj(u32 ufd, enum bpf_type *type)
{
        void *raw;

        raw = bpf_map_get_with_uref(ufd);
        if (!IS_ERR(raw)) {
                *type = BPF_TYPE_MAP;
                return raw;
        }

        raw = bpf_prog_get(ufd);
        if (!IS_ERR(raw)) {
                *type = BPF_TYPE_PROG;
                return raw;
        }

        raw = bpf_link_get_from_fd(ufd);
        if (!IS_ERR(raw)) {
                *type = BPF_TYPE_LINK;
                return raw;
        }

        return ERR_PTR(-EINVAL);
}

static const struct inode_operations bpf_dir_iops;

static const struct inode_operations bpf_prog_iops = { };
static const struct inode_operations bpf_map_iops  = { };
static const struct inode_operations bpf_link_iops  = { };

struct inode *bpf_get_inode(struct super_block *sb,
                            const struct inode *dir,
                            umode_t mode)
{
        struct inode *inode;

        switch (mode & S_IFMT) {
        case S_IFDIR:
        case S_IFREG:
        case S_IFLNK:
                break;
        default:
                return ERR_PTR(-EINVAL);
        }

        inode = new_inode(sb);
        if (!inode)
                return ERR_PTR(-ENOSPC);

        inode->i_ino = get_next_ino();
        simple_inode_init_ts(inode);

        inode_init_owner(&nop_mnt_idmap, inode, dir, mode);

        return inode;
}

static int bpf_inode_type(const struct inode *inode, enum bpf_type *type)
{
        *type = BPF_TYPE_UNSPEC;
        if (inode->i_op == &bpf_prog_iops)
                *type = BPF_TYPE_PROG;
        else if (inode->i_op == &bpf_map_iops)
                *type = BPF_TYPE_MAP;
        else if (inode->i_op == &bpf_link_iops)
                *type = BPF_TYPE_LINK;
        else
                return -EACCES;

        return 0;
}

static void bpf_dentry_finalize(struct dentry *dentry, struct inode *inode,
                                struct inode *dir)
{
        d_make_persistent(dentry, inode);

        inode_set_mtime_to_ts(dir, inode_set_ctime_current(dir));
}

static struct dentry *bpf_mkdir(struct mnt_idmap *idmap, struct inode *dir,
                                struct dentry *dentry, umode_t mode)
{
        struct inode *inode;

        inode = bpf_get_inode(dir->i_sb, dir, mode | S_IFDIR);
        if (IS_ERR(inode))
                return ERR_CAST(inode);

        inode->i_op = &bpf_dir_iops;
        inode->i_fop = &simple_dir_operations;

        inc_nlink(inode);
        inc_nlink(dir);

        bpf_dentry_finalize(dentry, inode, dir);
        return NULL;
}

struct map_iter {
        void *key;
        bool done;
};

static struct map_iter *map_iter(struct seq_file *m)
{
        return m->private;
}

static struct bpf_map *seq_file_to_map(struct seq_file *m)
{
        return file_inode(m->file)->i_private;
}

static void map_iter_free(struct map_iter *iter)
{
        if (iter) {
                kfree(iter->key);
                kfree(iter);
        }
}

static struct map_iter *map_iter_alloc(struct bpf_map *map)
{
        struct map_iter *iter;

        iter = kzalloc_obj(*iter, GFP_KERNEL | __GFP_NOWARN);
        if (!iter)
                goto error;

        iter->key = kzalloc(map->key_size, GFP_KERNEL | __GFP_NOWARN);
        if (!iter->key)
                goto error;

        return iter;

error:
        map_iter_free(iter);
        return NULL;
}

static void *map_seq_next(struct seq_file *m, void *v, loff_t *pos)
{
        struct bpf_map *map = seq_file_to_map(m);
        void *key = map_iter(m)->key;
        void *prev_key;

        (*pos)++;
        if (map_iter(m)->done)
                return NULL;

        if (unlikely(v == SEQ_START_TOKEN))
                prev_key = NULL;
        else
                prev_key = key;

        rcu_read_lock();
        if (map->ops->map_get_next_key(map, prev_key, key)) {
                map_iter(m)->done = true;
                key = NULL;
        }
        rcu_read_unlock();
        return key;
}

static void *map_seq_start(struct seq_file *m, loff_t *pos)
{
        if (map_iter(m)->done)
                return NULL;

        return *pos ? map_iter(m)->key : SEQ_START_TOKEN;
}

static void map_seq_stop(struct seq_file *m, void *v)
{
}

static int map_seq_show(struct seq_file *m, void *v)
{
        struct bpf_map *map = seq_file_to_map(m);
        void *key = map_iter(m)->key;

        if (unlikely(v == SEQ_START_TOKEN)) {
                seq_puts(m, "# WARNING!! The output is for debug purpose only\n");
                seq_puts(m, "# WARNING!! The output format will change\n");
        } else {
                map->ops->map_seq_show_elem(map, key, m);
        }

        return 0;
}

static const struct seq_operations bpffs_map_seq_ops = {
        .start  = map_seq_start,
        .next   = map_seq_next,
        .show   = map_seq_show,
        .stop   = map_seq_stop,
};

static int bpffs_map_open(struct inode *inode, struct file *file)
{
        struct bpf_map *map = inode->i_private;
        struct map_iter *iter;
        struct seq_file *m;
        int err;

        iter = map_iter_alloc(map);
        if (!iter)
                return -ENOMEM;

        err = seq_open(file, &bpffs_map_seq_ops);
        if (err) {
                map_iter_free(iter);
                return err;
        }

        m = file->private_data;
        m->private = iter;

        return 0;
}

static int bpffs_map_release(struct inode *inode, struct file *file)
{
        struct seq_file *m = file->private_data;

        map_iter_free(map_iter(m));

        return seq_release(inode, file);
}

/* bpffs_map_fops should only implement the basic
 * read operation for a BPF map.  The purpose is to
 * provide a simple user intuitive way to do
 * "cat bpffs/pathto/a-pinned-map".
 *
 * Other operations (e.g. write, lookup...) should be realized by
 * the userspace tools (e.g. bpftool) through the
 * BPF_OBJ_GET_INFO_BY_FD and the map's lookup/update
 * interface.
 */
static const struct file_operations bpffs_map_fops = {
        .open           = bpffs_map_open,
        .read           = seq_read,
        .release        = bpffs_map_release,
};

static int bpffs_obj_open(struct inode *inode, struct file *file)
{
        return -EIO;
}

static const struct file_operations bpffs_obj_fops = {
        .open           = bpffs_obj_open,
};

static int bpf_mkobj_ops(struct dentry *dentry, umode_t mode, void *raw,
                         const struct inode_operations *iops,
                         const struct file_operations *fops)
{
        struct inode *dir = dentry->d_parent->d_inode;
        struct inode *inode = bpf_get_inode(dir->i_sb, dir, mode);
        if (IS_ERR(inode))
                return PTR_ERR(inode);

        inode->i_op = iops;
        inode->i_fop = fops;
        inode->i_private = raw;

        bpf_dentry_finalize(dentry, inode, dir);
        return 0;
}

static int bpf_mkprog(struct dentry *dentry, umode_t mode, void *arg)
{
        return bpf_mkobj_ops(dentry, mode, arg, &bpf_prog_iops,
                             &bpffs_obj_fops);
}

static int bpf_mkmap(struct dentry *dentry, umode_t mode, void *arg)
{
        struct bpf_map *map = arg;

        return bpf_mkobj_ops(dentry, mode, arg, &bpf_map_iops,
                             bpf_map_support_seq_show(map) ?
                             &bpffs_map_fops : &bpffs_obj_fops);
}

static int bpf_mklink(struct dentry *dentry, umode_t mode, void *arg)
{
        struct bpf_link *link = arg;

        return bpf_mkobj_ops(dentry, mode, arg, &bpf_link_iops,
                             bpf_link_is_iter(link) ?
                             &bpf_iter_fops : &bpffs_obj_fops);
}

static struct dentry *
bpf_lookup(struct inode *dir, struct dentry *dentry, unsigned flags)
{
        /* Dots in names (e.g. "/sys/fs/bpf/foo.bar") are reserved for future
         * extensions. That allows popoulate_bpffs() create special files.
         */
        if ((dir->i_mode & S_IALLUGO) &&
            strchr(dentry->d_name.name, '.'))
                return ERR_PTR(-EPERM);

        return simple_lookup(dir, dentry, flags);
}

static int bpf_symlink(struct mnt_idmap *idmap, struct inode *dir,
                       struct dentry *dentry, const char *target)
{
        char *link = kstrdup(target, GFP_USER | __GFP_NOWARN);
        struct inode *inode;

        if (!link)
                return -ENOMEM;

        inode = bpf_get_inode(dir->i_sb, dir, S_IRWXUGO | S_IFLNK);
        if (IS_ERR(inode)) {
                kfree(link);
                return PTR_ERR(inode);
        }

        inode->i_op = &simple_symlink_inode_operations;
        inode->i_link = link;

        bpf_dentry_finalize(dentry, inode, dir);
        return 0;
}

static const struct inode_operations bpf_dir_iops = {
        .lookup         = bpf_lookup,
        .mkdir          = bpf_mkdir,
        .symlink        = bpf_symlink,
        .rmdir          = simple_rmdir,
        .rename         = simple_rename,
        .link           = simple_link,
        .unlink         = simple_unlink,
};

/* pin iterator link into bpffs */
static int bpf_iter_link_pin_kernel(struct dentry *parent,
                                    const char *name, struct bpf_link *link)
{
        umode_t mode = S_IFREG | S_IRUSR;
        struct dentry *dentry;
        int ret;

        dentry = simple_start_creating(parent, name);
        if (IS_ERR(dentry))
                return PTR_ERR(dentry);
        ret = bpf_mkobj_ops(dentry, mode, link, &bpf_link_iops,
                            &bpf_iter_fops);
        simple_done_creating(dentry);
        return ret;
}

static int bpf_obj_do_pin(int path_fd, const char __user *pathname, void *raw,
                          enum bpf_type type)
{
        struct dentry *dentry;
        struct inode *dir;
        struct path path;
        umode_t mode;
        int ret;

        dentry = start_creating_user_path(path_fd, pathname, &path, 0);
        if (IS_ERR(dentry))
                return PTR_ERR(dentry);

        dir = d_inode(path.dentry);
        if (dir->i_op != &bpf_dir_iops) {
                ret = -EPERM;
                goto out;
        }

        mode = S_IFREG | ((S_IRUSR | S_IWUSR) & ~current_umask());
        ret = security_path_mknod(&path, dentry, mode, 0);
        if (ret)
                goto out;

        switch (type) {
        case BPF_TYPE_PROG:
                ret = vfs_mkobj(dentry, mode, bpf_mkprog, raw);
                break;
        case BPF_TYPE_MAP:
                ret = vfs_mkobj(dentry, mode, bpf_mkmap, raw);
                break;
        case BPF_TYPE_LINK:
                ret = vfs_mkobj(dentry, mode, bpf_mklink, raw);
                break;
        default:
                ret = -EPERM;
        }
out:
        end_creating_path(&path, dentry);
        return ret;
}

int bpf_obj_pin_user(u32 ufd, int path_fd, const char __user *pathname)
{
        enum bpf_type type;
        void *raw;
        int ret;

        raw = bpf_fd_probe_obj(ufd, &type);
        if (IS_ERR(raw))
                return PTR_ERR(raw);

        ret = bpf_obj_do_pin(path_fd, pathname, raw, type);
        if (ret != 0)
                bpf_any_put(raw, type);

        return ret;
}

static void *bpf_obj_do_get(int path_fd, const char __user *pathname,
                            enum bpf_type *type, int flags)
{
        struct inode *inode;
        struct path path;
        void *raw;
        int ret;

        ret = user_path_at(path_fd, pathname, LOOKUP_FOLLOW, &path);
        if (ret)
                return ERR_PTR(ret);

        inode = d_backing_inode(path.dentry);
        ret = path_permission(&path, ACC_MODE(flags));
        if (ret)
                goto out;

        ret = bpf_inode_type(inode, type);
        if (ret)
                goto out;

        raw = bpf_any_get(inode->i_private, *type);
        if (!IS_ERR(raw))
                touch_atime(&path);

        path_put(&path);
        return raw;
out:
        path_put(&path);
        return ERR_PTR(ret);
}

int bpf_obj_get_user(int path_fd, const char __user *pathname, int flags)
{
        enum bpf_type type = BPF_TYPE_UNSPEC;
        int f_flags;
        void *raw;
        int ret;

        f_flags = bpf_get_file_flag(flags);
        if (f_flags < 0)
                return f_flags;

        raw = bpf_obj_do_get(path_fd, pathname, &type, f_flags);
        if (IS_ERR(raw))
                return PTR_ERR(raw);

        if (type == BPF_TYPE_PROG)
                ret = bpf_prog_new_fd(raw);
        else if (type == BPF_TYPE_MAP)
                ret = bpf_map_new_fd(raw, f_flags);
        else if (type == BPF_TYPE_LINK)
                ret = (f_flags != O_RDWR) ? -EINVAL : bpf_link_new_fd(raw);
        else
                return -ENOENT;

        if (ret < 0)
                bpf_any_put(raw, type);
        return ret;
}

static struct bpf_prog *__get_prog_inode(struct inode *inode, enum bpf_prog_type type)
{
        struct bpf_prog *prog;
        int ret = inode_permission(&nop_mnt_idmap, inode, MAY_READ);
        if (ret)
                return ERR_PTR(ret);

        if (inode->i_op == &bpf_map_iops)
                return ERR_PTR(-EINVAL);
        if (inode->i_op == &bpf_link_iops)
                return ERR_PTR(-EINVAL);
        if (inode->i_op != &bpf_prog_iops)
                return ERR_PTR(-EACCES);

        prog = inode->i_private;

        ret = security_bpf_prog(prog);
        if (ret < 0)
                return ERR_PTR(ret);

        if (!bpf_prog_get_ok(prog, &type, false))
                return ERR_PTR(-EINVAL);

        bpf_prog_inc(prog);
        return prog;
}

struct bpf_prog *bpf_prog_get_type_path(const char *name, enum bpf_prog_type type)
{
        struct bpf_prog *prog;
        struct path path;
        int ret = kern_path(name, LOOKUP_FOLLOW, &path);
        if (ret)
                return ERR_PTR(ret);
        prog = __get_prog_inode(d_backing_inode(path.dentry), type);
        if (!IS_ERR(prog))
                touch_atime(&path);
        path_put(&path);
        return prog;
}
EXPORT_SYMBOL(bpf_prog_get_type_path);

struct bpffs_btf_enums {
        const struct btf *btf;
        const struct btf_type *cmd_t;
        const struct btf_type *map_t;
        const struct btf_type *prog_t;
        const struct btf_type *attach_t;
};

static int find_bpffs_btf_enums(struct bpffs_btf_enums *info)
{
        struct {
                const struct btf_type **type;
                const char *name;
        } btf_enums[] = {
                {&info->cmd_t,          "bpf_cmd"},
                {&info->map_t,          "bpf_map_type"},
                {&info->prog_t,         "bpf_prog_type"},
                {&info->attach_t,       "bpf_attach_type"},
        };
        const struct btf *btf;
        int i, id;

        memset(info, 0, sizeof(*info));

        btf = bpf_get_btf_vmlinux();
        if (IS_ERR(btf))
                return PTR_ERR(btf);
        if (!btf)
                return -ENOENT;

        info->btf = btf;

        for (i = 0; i < ARRAY_SIZE(btf_enums); i++) {
                id = btf_find_by_name_kind(btf, btf_enums[i].name,
                                           BTF_KIND_ENUM);
                if (id < 0)
                        return -ESRCH;

                *btf_enums[i].type = btf_type_by_id(btf, id);
        }

        return 0;
}

static bool find_btf_enum_const(const struct btf *btf, const struct btf_type *enum_t,
                                const char *prefix, const char *str, int *value)
{
        const struct btf_enum *e;
        const char *name;
        int i, n, pfx_len = strlen(prefix);

        *value = 0;

        if (!btf || !enum_t)
                return false;

        for (i = 0, n = btf_vlen(enum_t); i < n; i++) {
                e = &btf_enum(enum_t)[i];

                name = btf_name_by_offset(btf, e->name_off);
                if (!name || strncasecmp(name, prefix, pfx_len) != 0)
                        continue;

                /* match symbolic name case insensitive and ignoring prefix */
                if (strcasecmp(name + pfx_len, str) == 0) {
                        *value = e->val;
                        return true;
                }
        }

        return false;
}

static void seq_print_delegate_opts(struct seq_file *m,
                                    const char *opt_name,
                                    const struct btf *btf,
                                    const struct btf_type *enum_t,
                                    const char *prefix,
                                    u64 delegate_msk, u64 any_msk)
{
        const struct btf_enum *e;
        bool first = true;
        const char *name;
        u64 msk;
        int i, n, pfx_len = strlen(prefix);

        delegate_msk &= any_msk; /* clear unknown bits */

        if (delegate_msk == 0)
                return;

        seq_printf(m, ",%s", opt_name);
        if (delegate_msk == any_msk) {
                seq_printf(m, "=any");
                return;
        }

        if (btf && enum_t) {
                for (i = 0, n = btf_vlen(enum_t); i < n; i++) {
                        e = &btf_enum(enum_t)[i];
                        name = btf_name_by_offset(btf, e->name_off);
                        if (!name || strncasecmp(name, prefix, pfx_len) != 0)
                                continue;
                        msk = 1ULL << e->val;
                        if (delegate_msk & msk) {
                                /* emit lower-case name without prefix */
                                seq_putc(m, first ? '=' : ':');
                                name += pfx_len;
                                while (*name) {
                                        seq_putc(m, tolower(*name));
                                        name++;
                                }

                                delegate_msk &= ~msk;
                                first = false;
                        }
                }
        }
        if (delegate_msk)
                seq_printf(m, "%c0x%llx", first ? '=' : ':', delegate_msk);
}

/*
 * Display the mount options in /proc/mounts.
 */
static int bpf_show_options(struct seq_file *m, struct dentry *root)
{
        struct inode *inode = d_inode(root);
        umode_t mode = inode->i_mode & S_IALLUGO & ~S_ISVTX;
        struct bpf_mount_opts *opts = root->d_sb->s_fs_info;
        u64 mask;

        if (!uid_eq(inode->i_uid, GLOBAL_ROOT_UID))
                seq_printf(m, ",uid=%u",
                           from_kuid_munged(&init_user_ns, inode->i_uid));
        if (!gid_eq(inode->i_gid, GLOBAL_ROOT_GID))
                seq_printf(m, ",gid=%u",
                           from_kgid_munged(&init_user_ns, inode->i_gid));
        if (mode != S_IRWXUGO)
                seq_printf(m, ",mode=%o", mode);

        if (opts->delegate_cmds || opts->delegate_maps ||
            opts->delegate_progs || opts->delegate_attachs) {
                struct bpffs_btf_enums info;

                /* ignore errors, fallback to hex */
                (void)find_bpffs_btf_enums(&info);

                mask = (1ULL << __MAX_BPF_CMD) - 1;
                seq_print_delegate_opts(m, "delegate_cmds",
                                        info.btf, info.cmd_t, "BPF_",
                                        opts->delegate_cmds, mask);

                mask = (1ULL << __MAX_BPF_MAP_TYPE) - 1;
                seq_print_delegate_opts(m, "delegate_maps",
                                        info.btf, info.map_t, "BPF_MAP_TYPE_",
                                        opts->delegate_maps, mask);

                mask = (1ULL << __MAX_BPF_PROG_TYPE) - 1;
                seq_print_delegate_opts(m, "delegate_progs",
                                        info.btf, info.prog_t, "BPF_PROG_TYPE_",
                                        opts->delegate_progs, mask);

                mask = (1ULL << __MAX_BPF_ATTACH_TYPE) - 1;
                seq_print_delegate_opts(m, "delegate_attachs",
                                        info.btf, info.attach_t, "BPF_",
                                        opts->delegate_attachs, mask);
        }

        return 0;
}

static void bpf_destroy_inode(struct inode *inode)
{
        enum bpf_type type;

        if (S_ISLNK(inode->i_mode))
                kfree(inode->i_link);
        if (!bpf_inode_type(inode, &type))
                bpf_any_put(inode->i_private, type);
        free_inode_nonrcu(inode);
}

const struct super_operations bpf_super_ops = {
        .statfs         = simple_statfs,
        .drop_inode     = inode_just_drop,
        .show_options   = bpf_show_options,
        .destroy_inode  = bpf_destroy_inode,
};

enum {
        OPT_UID,
        OPT_GID,
        OPT_MODE,
        OPT_DELEGATE_CMDS,
        OPT_DELEGATE_MAPS,
        OPT_DELEGATE_PROGS,
        OPT_DELEGATE_ATTACHS,
};

static const struct fs_parameter_spec bpf_fs_parameters[] = {
        fsparam_u32     ("uid",                         OPT_UID),
        fsparam_u32     ("gid",                         OPT_GID),
        fsparam_u32oct  ("mode",                        OPT_MODE),
        fsparam_string  ("delegate_cmds",               OPT_DELEGATE_CMDS),
        fsparam_string  ("delegate_maps",               OPT_DELEGATE_MAPS),
        fsparam_string  ("delegate_progs",              OPT_DELEGATE_PROGS),
        fsparam_string  ("delegate_attachs",            OPT_DELEGATE_ATTACHS),
        {}
};

static int bpf_parse_param(struct fs_context *fc, struct fs_parameter *param)
{
        struct bpf_mount_opts *opts = fc->s_fs_info;
        struct fs_parse_result result;
        kuid_t uid;
        kgid_t gid;
        int opt, err;

        opt = fs_parse(fc, bpf_fs_parameters, param, &result);
        if (opt < 0) {
                /* We might like to report bad mount options here, but
                 * traditionally we've ignored all mount options, so we'd
                 * better continue to ignore non-existing options for bpf.
                 */
                if (opt == -ENOPARAM) {
                        opt = vfs_parse_fs_param_source(fc, param);
                        if (opt != -ENOPARAM)
                                return opt;

                        return 0;
                }

                if (opt < 0)
                        return opt;
        }

        switch (opt) {
        case OPT_UID:
                uid = make_kuid(current_user_ns(), result.uint_32);
                if (!uid_valid(uid))
                        goto bad_value;

                /*
                 * The requested uid must be representable in the
                 * filesystem's idmapping.
                 */
                if (!kuid_has_mapping(fc->user_ns, uid))
                        goto bad_value;

                opts->uid = uid;
                break;
        case OPT_GID:
                gid = make_kgid(current_user_ns(), result.uint_32);
                if (!gid_valid(gid))
                        goto bad_value;

                /*
                 * The requested gid must be representable in the
                 * filesystem's idmapping.
                 */
                if (!kgid_has_mapping(fc->user_ns, gid))
                        goto bad_value;

                opts->gid = gid;
                break;
        case OPT_MODE:
                opts->mode = result.uint_32 & S_IALLUGO;
                break;
        case OPT_DELEGATE_CMDS:
        case OPT_DELEGATE_MAPS:
        case OPT_DELEGATE_PROGS:
        case OPT_DELEGATE_ATTACHS: {
                struct bpffs_btf_enums info;
                const struct btf_type *enum_t;
                const char *enum_pfx;
                u64 *delegate_msk, msk = 0;
                char *p, *str;
                int val;

                /* ignore errors, fallback to hex */
                (void)find_bpffs_btf_enums(&info);

                switch (opt) {
                case OPT_DELEGATE_CMDS:
                        delegate_msk = &opts->delegate_cmds;
                        enum_t = info.cmd_t;
                        enum_pfx = "BPF_";
                        break;
                case OPT_DELEGATE_MAPS:
                        delegate_msk = &opts->delegate_maps;
                        enum_t = info.map_t;
                        enum_pfx = "BPF_MAP_TYPE_";
                        break;
                case OPT_DELEGATE_PROGS:
                        delegate_msk = &opts->delegate_progs;
                        enum_t = info.prog_t;
                        enum_pfx = "BPF_PROG_TYPE_";
                        break;
                case OPT_DELEGATE_ATTACHS:
                        delegate_msk = &opts->delegate_attachs;
                        enum_t = info.attach_t;
                        enum_pfx = "BPF_";
                        break;
                default:
                        return -EINVAL;
                }

                str = param->string;
                while ((p = strsep(&str, ":"))) {
                        if (strcmp(p, "any") == 0) {
                                msk |= ~0ULL;
                        } else if (find_btf_enum_const(info.btf, enum_t, enum_pfx, p, &val)) {
                                msk |= 1ULL << val;
                        } else {
                                err = kstrtou64(p, 0, &msk);
                                if (err)
                                        return err;
                        }
                }

                /* Setting delegation mount options requires privileges */
                if (msk && !capable(CAP_SYS_ADMIN))
                        return -EPERM;

                *delegate_msk |= msk;
                break;
        }
        default:
                /* ignore unknown mount options */
                break;
        }

        return 0;
bad_value:
        return invalfc(fc, "Bad value for '%s'", param->key);
}

struct bpf_preload_ops *bpf_preload_ops;
EXPORT_SYMBOL_GPL(bpf_preload_ops);

static bool bpf_preload_mod_get(void)
{
        /* If bpf_preload.ko wasn't loaded earlier then load it now.
         * When bpf_preload is built into vmlinux the module's __init
         * function will populate it.
         */
        if (!bpf_preload_ops) {
                request_module("bpf_preload");
                if (!bpf_preload_ops)
                        return false;
        }
        /* And grab the reference, so the module doesn't disappear while the
         * kernel is interacting with the kernel module and its UMD.
         */
        if (!try_module_get(bpf_preload_ops->owner)) {
                pr_err("bpf_preload module get failed.\n");
                return false;
        }
        return true;
}

static void bpf_preload_mod_put(void)
{
        if (bpf_preload_ops)
                /* now user can "rmmod bpf_preload" if necessary */
                module_put(bpf_preload_ops->owner);
}

static DEFINE_MUTEX(bpf_preload_lock);

static int populate_bpffs(struct dentry *parent)
{
        struct bpf_preload_info objs[BPF_PRELOAD_LINKS] = {};
        int err = 0, i;

        /* grab the mutex to make sure the kernel interactions with bpf_preload
         * are serialized
         */
        mutex_lock(&bpf_preload_lock);

        /* if bpf_preload.ko wasn't built into vmlinux then load it */
        if (!bpf_preload_mod_get())
                goto out;

        err = bpf_preload_ops->preload(objs);
        if (err)
                goto out_put;
        for (i = 0; i < BPF_PRELOAD_LINKS; i++) {
                bpf_link_inc(objs[i].link);
                err = bpf_iter_link_pin_kernel(parent,
                                               objs[i].link_name, objs[i].link);
                if (err) {
                        bpf_link_put(objs[i].link);
                        goto out_put;
                }
        }
out_put:
        bpf_preload_mod_put();
out:
        mutex_unlock(&bpf_preload_lock);
        return err;
}

static int bpf_fill_super(struct super_block *sb, struct fs_context *fc)
{
        static const struct tree_descr bpf_rfiles[] = { { "" } };
        struct bpf_mount_opts *opts = sb->s_fs_info;
        struct inode *inode;
        int ret;

        /* Mounting an instance of BPF FS requires privileges */
        if (fc->user_ns != &init_user_ns && !capable(CAP_SYS_ADMIN))
                return -EPERM;

        ret = simple_fill_super(sb, BPF_FS_MAGIC, bpf_rfiles);
        if (ret)
                return ret;

        sb->s_op = &bpf_super_ops;

        inode = sb->s_root->d_inode;
        inode->i_uid = opts->uid;
        inode->i_gid = opts->gid;
        inode->i_op = &bpf_dir_iops;
        inode->i_mode &= ~S_IALLUGO;
        populate_bpffs(sb->s_root);
        inode->i_mode |= S_ISVTX | opts->mode;
        return 0;
}

static int bpf_get_tree(struct fs_context *fc)
{
        return get_tree_nodev(fc, bpf_fill_super);
}

static void bpf_free_fc(struct fs_context *fc)
{
        kfree(fc->s_fs_info);
}

static const struct fs_context_operations bpf_context_ops = {
        .free           = bpf_free_fc,
        .parse_param    = bpf_parse_param,
        .get_tree       = bpf_get_tree,
};

/*
 * Set up the filesystem mount context.
 */
static int bpf_init_fs_context(struct fs_context *fc)
{
        struct bpf_mount_opts *opts;

        opts = kzalloc_obj(struct bpf_mount_opts);
        if (!opts)
                return -ENOMEM;

        opts->mode = S_IRWXUGO;
        opts->uid = current_fsuid();
        opts->gid = current_fsgid();

        /* start out with no BPF token delegation enabled */
        opts->delegate_cmds = 0;
        opts->delegate_maps = 0;
        opts->delegate_progs = 0;
        opts->delegate_attachs = 0;

        fc->s_fs_info = opts;
        fc->ops = &bpf_context_ops;
        return 0;
}

static void bpf_kill_super(struct super_block *sb)
{
        struct bpf_mount_opts *opts = sb->s_fs_info;

        kill_anon_super(sb);
        kfree(opts);
}

static struct file_system_type bpf_fs_type = {
        .owner          = THIS_MODULE,
        .name           = "bpf",
        .init_fs_context = bpf_init_fs_context,
        .parameters     = bpf_fs_parameters,
        .kill_sb        = bpf_kill_super,
        .fs_flags       = FS_USERNS_MOUNT,
};

static int __init bpf_init(void)
{
        int ret;

        ret = sysfs_create_mount_point(fs_kobj, "bpf");
        if (ret)
                return ret;

        ret = register_filesystem(&bpf_fs_type);
        if (ret)
                sysfs_remove_mount_point(fs_kobj, "bpf");

        return ret;
}
fs_initcall(bpf_init);