/*
 * Minimal file system backend for holding eBPF maps and programs,
 * used by bpf(2) object pinning.
 *
 * Authors:
 *
 *      Daniel Borkmann <daniel@iogearbox.net>
 *
 * This program is free software; you can redistribute it and/or
 * modify it under the terms of the GNU General Public License
 * version 2 as published by the Free Software Foundation.
 */

#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/kdev_t.h>
#include <linux/parser.h>
#include <linux/filter.h>
#include <linux/bpf.h>
#include <linux/bpf_trace.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  = { };

static 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();
        inode->i_atime = current_time(inode);
        inode->i_mtime = inode->i_atime;
        inode->i_ctime = inode->i_atime;

        inode_init_owner(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_instantiate(dentry, inode);
        dget(dentry);

        dir->i_mtime = current_time(dir);
        dir->i_ctime = dir->i_mtime;
}

static int bpf_mkdir(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 PTR_ERR(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 0;
}

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(sizeof(*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;

        if (map->ops->map_get_next_key(map, prev_key, key)) {
                map_iter(m)->done = true;
                return NULL;
        }
        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)
{
        return bpf_mkobj_ops(dentry, mode, arg, &bpf_link_iops,
                             &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.
         */
        if (strchr(dentry->d_name.name, '.'))
                return ERR_PTR(-EPERM);

        return simple_lookup(dir, dentry, flags);
}

static int bpf_symlink(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,
};

static int bpf_obj_do_pin(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 = user_path_create(AT_FDCWD, pathname, &path, 0);
        if (IS_ERR(dentry))
                return PTR_ERR(dentry);

        mode = S_IFREG | ((S_IRUSR | S_IWUSR) & ~current_umask());

        ret = security_path_mknod(&path, dentry, mode, 0);
        if (ret)
                goto out;

        dir = d_inode(path.dentry);
        if (dir->i_op != &bpf_dir_iops) {
                ret = -EPERM;
                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:
        done_path_create(&path, dentry);
        return ret;
}

int bpf_obj_pin_user(u32 ufd, 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(pathname, raw, type);
        if (ret != 0)
                bpf_any_put(raw, type);

        return ret;
}

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

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

        inode = d_backing_inode(path.dentry);
        ret = inode_permission(inode, 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(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(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 = 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(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);

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

        if (mode != S_IRWXUGO)
                seq_printf(m, ",mode=%o", mode);
        return 0;
}

static void bpf_destroy_inode_deferred(struct rcu_head *head)
{
        struct inode *inode = container_of(head, struct inode, i_rcu);
        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);
}

static void bpf_destroy_inode(struct inode *inode)
{
        call_rcu(&inode->i_rcu, bpf_destroy_inode_deferred);
}

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

enum {
        OPT_MODE,
        OPT_ERR,
};

static const match_table_t bpf_mount_tokens = {
        { OPT_MODE, "mode=%o" },
        { OPT_ERR, NULL },
};

struct bpf_mount_opts {
        umode_t mode;
};

static int bpf_parse_options(char *data, struct bpf_mount_opts *opts)
{
        substring_t args[MAX_OPT_ARGS];
        int option, token;
        char *ptr;

        opts->mode = S_IRWXUGO;

        while ((ptr = strsep(&data, ",")) != NULL) {
                if (!*ptr)
                        continue;

                token = match_token(ptr, bpf_mount_tokens, args);
                switch (token) {
                case OPT_MODE:
                        if (match_octal(&args[0], &option))
                                return -EINVAL;
                        opts->mode = option & S_IALLUGO;
                        break;
                /* 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.
                 */
                }
        }

        return 0;
}

static int bpf_fill_super(struct super_block *sb, void *data, int silent)
{
        static const struct tree_descr bpf_rfiles[] = { { "" } };
        struct bpf_mount_opts opts;
        struct inode *inode;
        int ret;

        ret = bpf_parse_options(data, &opts);
        if (ret)
                return ret;

        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_op = &bpf_dir_iops;
        inode->i_mode &= ~S_IALLUGO;
        inode->i_mode |= S_ISVTX | opts.mode;

        return 0;
}

static struct dentry *bpf_mount(struct file_system_type *type, int flags,
                                const char *dev_name, void *data)
{
        return mount_nodev(type, flags, data, bpf_fill_super);
}

static struct file_system_type bpf_fs_type = {
        .owner          = THIS_MODULE,
        .name           = "bpf",
        .mount          = bpf_mount,
        .kill_sb        = kill_litter_super,
};

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);