kernel/bpf/inode.c

   1 /*
   2  * Minimal file system backend for holding eBPF maps and programs,
   3  * used by bpf(2) object pinning.
   4  *
   5  * Authors:
   6  *
   7  *      Daniel Borkmann <daniel@iogearbox.net>
   8  *
   9  * This program is free software; you can redistribute it and/or
  10  * modify it under the terms of the GNU General Public License
  11  * version 2 as published by the Free Software Foundation.
  12  */
  13
  14 #include <linux/module.h>
  15 #include <linux/magic.h>
  16 #include <linux/major.h>
  17 #include <linux/mount.h>
  18 #include <linux/namei.h>
  19 #include <linux/fs.h>
  20 #include <linux/kdev_t.h>
  21 #include <linux/filter.h>
  22 #include <linux/bpf.h>
  23
  24 enum bpf_type {
  25         BPF_TYPE_UNSPEC = 0,
  26         BPF_TYPE_PROG,
  27         BPF_TYPE_MAP,
  28 };
  29
  30 static void *bpf_any_get(void *raw, enum bpf_type type)
  31 {
  32         switch (type) {
  33         case BPF_TYPE_PROG:
  34                 atomic_inc(&((struct bpf_prog *)raw)->aux->refcnt);
  35                 break;
  36         case BPF_TYPE_MAP:
  37                 bpf_map_inc(raw, true);
  38                 break;
  39         default:
  40                 WARN_ON_ONCE(1);
  41                 break;
  42         }
  43
  44         return raw;
  45 }
  46
  47 static void bpf_any_put(void *raw, enum bpf_type type)
  48 {
  49         switch (type) {
  50         case BPF_TYPE_PROG:
  51                 bpf_prog_put(raw);
  52                 break;
  53         case BPF_TYPE_MAP:
  54                 bpf_map_put_with_uref(raw);
  55                 break;
  56         default:
  57                 WARN_ON_ONCE(1);
  58                 break;
  59         }
  60 }
  61
  62 static void *bpf_fd_probe_obj(u32 ufd, enum bpf_type *type)
  63 {
  64         void *raw;
  65
  66         *type = BPF_TYPE_MAP;
  67         raw = bpf_map_get_with_uref(ufd);
  68         if (IS_ERR(raw)) {
  69                 *type = BPF_TYPE_PROG;
  70                 raw = bpf_prog_get(ufd);
  71         }
  72
  73         return raw;
  74 }
  75
  76 static const struct inode_operations bpf_dir_iops;
  77
  78 static const struct inode_operations bpf_prog_iops = { };
  79 static const struct inode_operations bpf_map_iops  = { };
  80
  81 static struct inode *bpf_get_inode(struct super_block *sb,
  82                                    const struct inode *dir,
  83                                    umode_t mode)
  84 {
  85         struct inode *inode;
  86
  87         switch (mode & S_IFMT) {
  88         case S_IFDIR:
  89         case S_IFREG:
  90                 break;
  91         default:
  92                 return ERR_PTR(-EINVAL);
  93         }
  94
  95         inode = new_inode(sb);
  96         if (!inode)
  97                 return ERR_PTR(-ENOSPC);
  98
  99         inode->i_ino = get_next_ino();
 100         inode->i_atime = CURRENT_TIME;
 101         inode->i_mtime = inode->i_atime;
 102         inode->i_ctime = inode->i_atime;
 103
 104         inode_init_owner(inode, dir, mode);
 105
 106         return inode;
 107 }
 108
 109 static int bpf_inode_type(const struct inode *inode, enum bpf_type *type)
 110 {
 111         *type = BPF_TYPE_UNSPEC;
 112         if (inode->i_op == &bpf_prog_iops)
 113                 *type = BPF_TYPE_PROG;
 114         else if (inode->i_op == &bpf_map_iops)
 115                 *type = BPF_TYPE_MAP;
 116         else
 117                 return -EACCES;
 118
 119         return 0;
 120 }
 121
 122 static bool bpf_dname_reserved(const struct dentry *dentry)
 123 {
 124         return strchr(dentry->d_name.name, '.');
 125 }
 126
 127 static int bpf_mkdir(struct inode *dir, struct dentry *dentry, umode_t mode)
 128 {
 129         struct inode *inode;
 130
 131         if (bpf_dname_reserved(dentry))
 132                 return -EPERM;
 133
 134         inode = bpf_get_inode(dir->i_sb, dir, mode | S_IFDIR);
 135         if (IS_ERR(inode))
 136                 return PTR_ERR(inode);
 137
 138         inode->i_op = &bpf_dir_iops;
 139         inode->i_fop = &simple_dir_operations;
 140
 141         inc_nlink(inode);
 142         inc_nlink(dir);
 143
 144         d_instantiate(dentry, inode);
 145         dget(dentry);
 146
 147         return 0;
 148 }
 149
 150 static int bpf_mkobj_ops(struct inode *dir, struct dentry *dentry,
 151                          umode_t mode, const struct inode_operations *iops)
 152 {
 153         struct inode *inode;
 154
 155         if (bpf_dname_reserved(dentry))
 156                 return -EPERM;
 157
 158         inode = bpf_get_inode(dir->i_sb, dir, mode | S_IFREG);
 159         if (IS_ERR(inode))
 160                 return PTR_ERR(inode);
 161
 162         inode->i_op = iops;
 163         inode->i_private = dentry->d_fsdata;
 164
 165         d_instantiate(dentry, inode);
 166         dget(dentry);
 167
 168         return 0;
 169 }
 170
 171 static int bpf_mkobj(struct inode *dir, struct dentry *dentry, umode_t mode,
 172                      dev_t devt)
 173 {
 174         enum bpf_type type = MINOR(devt);
 175
 176         if (MAJOR(devt) != UNNAMED_MAJOR || !S_ISREG(mode) ||
 177             dentry->d_fsdata == NULL)
 178                 return -EPERM;
 179
 180         switch (type) {
 181         case BPF_TYPE_PROG:
 182                 return bpf_mkobj_ops(dir, dentry, mode, &bpf_prog_iops);
 183         case BPF_TYPE_MAP:
 184                 return bpf_mkobj_ops(dir, dentry, mode, &bpf_map_iops);
 185         default:
 186                 return -EPERM;
 187         }
 188 }
 189
 190 static int bpf_link(struct dentry *old_dentry, struct inode *dir,
 191                     struct dentry *new_dentry)
 192 {
 193         if (bpf_dname_reserved(new_dentry))
 194                 return -EPERM;
 195
 196         return simple_link(old_dentry, dir, new_dentry);
 197 }
 198
 199 static int bpf_rename(struct inode *old_dir, struct dentry *old_dentry,
 200                       struct inode *new_dir, struct dentry *new_dentry)
 201 {
 202         if (bpf_dname_reserved(new_dentry))
 203                 return -EPERM;
 204
 205         return simple_rename(old_dir, old_dentry, new_dir, new_dentry);
 206 }
 207
 208 static const struct inode_operations bpf_dir_iops = {
 209         .lookup         = simple_lookup,
 210         .mknod          = bpf_mkobj,
 211         .mkdir          = bpf_mkdir,
 212         .rmdir          = simple_rmdir,
 213         .rename         = bpf_rename,
 214         .link           = bpf_link,
 215         .unlink         = simple_unlink,
 216 };
 217
 218 static int bpf_obj_do_pin(const struct filename *pathname, void *raw,
 219                           enum bpf_type type)
 220 {
 221         struct dentry *dentry;
 222         struct inode *dir;
 223         struct path path;
 224         umode_t mode;
 225         dev_t devt;
 226         int ret;
 227
 228         dentry = kern_path_create(AT_FDCWD, pathname->name, &path, 0);
 229         if (IS_ERR(dentry))
 230                 return PTR_ERR(dentry);
 231
 232         mode = S_IFREG | ((S_IRUSR | S_IWUSR) & ~current_umask());
 233         devt = MKDEV(UNNAMED_MAJOR, type);
 234
 235         ret = security_path_mknod(&path, dentry, mode, devt);
 236         if (ret)
 237                 goto out;
 238
 239         dir = d_inode(path.dentry);
 240         if (dir->i_op != &bpf_dir_iops) {
 241                 ret = -EPERM;
 242                 goto out;
 243         }
 244
 245         dentry->d_fsdata = raw;
 246         ret = vfs_mknod(dir, dentry, mode, devt);
 247         dentry->d_fsdata = NULL;
 248 out:
 249         done_path_create(&path, dentry);
 250         return ret;
 251 }
 252
 253 int bpf_obj_pin_user(u32 ufd, const char __user *pathname)
 254 {
 255         struct filename *pname;
 256         enum bpf_type type;
 257         void *raw;
 258         int ret;
 259
 260         pname = getname(pathname);
 261         if (IS_ERR(pname))
 262                 return PTR_ERR(pname);
 263
 264         raw = bpf_fd_probe_obj(ufd, &type);
 265         if (IS_ERR(raw)) {
 266                 ret = PTR_ERR(raw);
 267                 goto out;
 268         }
 269
 270         ret = bpf_obj_do_pin(pname, raw, type);
 271         if (ret != 0)
 272                 bpf_any_put(raw, type);
 273 out:
 274         putname(pname);
 275         return ret;
 276 }
 277
 278 static void *bpf_obj_do_get(const struct filename *pathname,
 279                             enum bpf_type *type)
 280 {
 281         struct inode *inode;
 282         struct path path;
 283         void *raw;
 284         int ret;
 285
 286         ret = kern_path(pathname->name, LOOKUP_FOLLOW, &path);
 287         if (ret)
 288                 return ERR_PTR(ret);
 289
 290         inode = d_backing_inode(path.dentry);
 291         ret = inode_permission(inode, MAY_WRITE);
 292         if (ret)
 293                 goto out;
 294
 295         ret = bpf_inode_type(inode, type);
 296         if (ret)
 297                 goto out;
 298
 299         raw = bpf_any_get(inode->i_private, *type);
 300         touch_atime(&path);
 301
 302         path_put(&path);
 303         return raw;
 304 out:
 305         path_put(&path);
 306         return ERR_PTR(ret);
 307 }
 308
 309 int bpf_obj_get_user(const char __user *pathname)
 310 {
 311         enum bpf_type type = BPF_TYPE_UNSPEC;
 312         struct filename *pname;
 313         int ret = -ENOENT;
 314         void *raw;
 315
 316         pname = getname(pathname);
 317         if (IS_ERR(pname))
 318                 return PTR_ERR(pname);
 319
 320         raw = bpf_obj_do_get(pname, &type);
 321         if (IS_ERR(raw)) {
 322                 ret = PTR_ERR(raw);
 323                 goto out;
 324         }
 325
 326         if (type == BPF_TYPE_PROG)
 327                 ret = bpf_prog_new_fd(raw);
 328         else if (type == BPF_TYPE_MAP)
 329                 ret = bpf_map_new_fd(raw);
 330         else
 331                 goto out;
 332
 333         if (ret < 0)
 334                 bpf_any_put(raw, type);
 335 out:
 336         putname(pname);
 337         return ret;
 338 }
 339
 340 static void bpf_evict_inode(struct inode *inode)
 341 {
 342         enum bpf_type type;
 343
 344         truncate_inode_pages_final(&inode->i_data);
 345         clear_inode(inode);
 346
 347         if (!bpf_inode_type(inode, &type))
 348                 bpf_any_put(inode->i_private, type);
 349 }
 350
 351 static const struct super_operations bpf_super_ops = {
 352         .statfs         = simple_statfs,
 353         .drop_inode     = generic_delete_inode,
 354         .evict_inode    = bpf_evict_inode,
 355 };
 356
 357 static int bpf_fill_super(struct super_block *sb, void *data, int silent)
 358 {
 359         static struct tree_descr bpf_rfiles[] = { { "" } };
 360         struct inode *inode;
 361         int ret;
 362
 363         ret = simple_fill_super(sb, BPF_FS_MAGIC, bpf_rfiles);
 364         if (ret)
 365                 return ret;
 366
 367         sb->s_op = &bpf_super_ops;
 368
 369         inode = sb->s_root->d_inode;
 370         inode->i_op = &bpf_dir_iops;
 371         inode->i_mode &= ~S_IALLUGO;
 372         inode->i_mode |= S_ISVTX | S_IRWXUGO;
 373
 374         return 0;
 375 }
 376
 377 static struct dentry *bpf_mount(struct file_system_type *type, int flags,
 378                                 const char *dev_name, void *data)
 379 {
 380         return mount_ns(type, flags, current->nsproxy->mnt_ns, bpf_fill_super);
 381 }
 382
 383 static struct file_system_type bpf_fs_type = {
 384         .owner          = THIS_MODULE,
 385         .name           = "bpf",
 386         .mount          = bpf_mount,
 387         .kill_sb        = kill_litter_super,
 388         .fs_flags       = FS_USERNS_MOUNT,
 389 };
 390
 391 MODULE_ALIAS_FS("bpf");
 392
 393 static int __init bpf_init(void)
 394 {
 395         int ret;
 396
 397         ret = sysfs_create_mount_point(fs_kobj, "bpf");
 398         if (ret)
 399                 return ret;
 400
 401         ret = register_filesystem(&bpf_fs_type);
 402         if (ret)
 403                 sysfs_remove_mount_point(fs_kobj, "bpf");
 404
 405         return ret;
 406 }
 407 fs_initcall(bpf_init);