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/init.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/parser.h>
  22 #include <linux/filter.h>
  23 #include <linux/bpf.h>
  24
  25 enum bpf_type {
  26         BPF_TYPE_UNSPEC = 0,
  27         BPF_TYPE_PROG,
  28         BPF_TYPE_MAP,
  29 };
  30
  31 static void *bpf_any_get(void *raw, enum bpf_type type)
  32 {
  33         switch (type) {
  34         case BPF_TYPE_PROG:
  35                 raw = bpf_prog_inc(raw);
  36                 break;
  37         case BPF_TYPE_MAP:
  38                 raw = bpf_map_inc(raw, true);
  39                 break;
  40         default:
  41                 WARN_ON_ONCE(1);
  42                 break;
  43         }
  44
  45         return raw;
  46 }
  47
  48 static void bpf_any_put(void *raw, enum bpf_type type)
  49 {
  50         switch (type) {
  51         case BPF_TYPE_PROG:
  52                 bpf_prog_put(raw);
  53                 break;
  54         case BPF_TYPE_MAP:
  55                 bpf_map_put_with_uref(raw);
  56                 break;
  57         default:
  58                 WARN_ON_ONCE(1);
  59                 break;
  60         }
  61 }
  62
  63 static void *bpf_fd_probe_obj(u32 ufd, enum bpf_type *type)
  64 {
  65         void *raw;
  66
  67         *type = BPF_TYPE_MAP;
  68         raw = bpf_map_get_with_uref(ufd);
  69         if (IS_ERR(raw)) {
  70                 *type = BPF_TYPE_PROG;
  71                 raw = bpf_prog_get(ufd);
  72         }
  73
  74         return raw;
  75 }
  76
  77 static const struct inode_operations bpf_dir_iops;
  78
  79 static const struct inode_operations bpf_prog_iops = { };
  80 static const struct inode_operations bpf_map_iops  = { };
  81
  82 static struct inode *bpf_get_inode(struct super_block *sb,
  83                                    const struct inode *dir,
  84                                    umode_t mode)
  85 {
  86         struct inode *inode;
  87
  88         switch (mode & S_IFMT) {
  89         case S_IFDIR:
  90         case S_IFREG:
  91         case S_IFLNK:
  92                 break;
  93         default:
  94                 return ERR_PTR(-EINVAL);
  95         }
  96
  97         inode = new_inode(sb);
  98         if (!inode)
  99                 return ERR_PTR(-ENOSPC);
 100
 101         inode->i_ino = get_next_ino();
 102         inode->i_atime = current_time(inode);
 103         inode->i_mtime = inode->i_atime;
 104         inode->i_ctime = inode->i_atime;
 105
 106         inode_init_owner(inode, dir, mode);
 107
 108         return inode;
 109 }
 110
 111 static int bpf_inode_type(const struct inode *inode, enum bpf_type *type)
 112 {
 113         *type = BPF_TYPE_UNSPEC;
 114         if (inode->i_op == &bpf_prog_iops)
 115                 *type = BPF_TYPE_PROG;
 116         else if (inode->i_op == &bpf_map_iops)
 117                 *type = BPF_TYPE_MAP;
 118         else
 119                 return -EACCES;
 120
 121         return 0;
 122 }
 123
 124 static void bpf_dentry_finalize(struct dentry *dentry, struct inode *inode,
 125                                 struct inode *dir)
 126 {
 127         d_instantiate(dentry, inode);
 128         dget(dentry);
 129
 130         dir->i_mtime = current_time(dir);
 131         dir->i_ctime = dir->i_mtime;
 132 }
 133
 134 static int bpf_mkdir(struct inode *dir, struct dentry *dentry, umode_t mode)
 135 {
 136         struct inode *inode;
 137
 138         inode = bpf_get_inode(dir->i_sb, dir, mode | S_IFDIR);
 139         if (IS_ERR(inode))
 140                 return PTR_ERR(inode);
 141
 142         inode->i_op = &bpf_dir_iops;
 143         inode->i_fop = &simple_dir_operations;
 144
 145         inc_nlink(inode);
 146         inc_nlink(dir);
 147
 148         bpf_dentry_finalize(dentry, inode, dir);
 149         return 0;
 150 }
 151
 152 static int bpf_mkobj_ops(struct inode *dir, struct dentry *dentry,
 153                          umode_t mode, const struct inode_operations *iops)
 154 {
 155         struct inode *inode;
 156
 157         inode = bpf_get_inode(dir->i_sb, dir, mode | S_IFREG);
 158         if (IS_ERR(inode))
 159                 return PTR_ERR(inode);
 160
 161         inode->i_op = iops;
 162         inode->i_private = dentry->d_fsdata;
 163
 164         bpf_dentry_finalize(dentry, inode, dir);
 165         return 0;
 166 }
 167
 168 static int bpf_mkobj(struct inode *dir, struct dentry *dentry, umode_t mode,
 169                      dev_t devt)
 170 {
 171         enum bpf_type type = MINOR(devt);
 172
 173         if (MAJOR(devt) != UNNAMED_MAJOR || !S_ISREG(mode) ||
 174             dentry->d_fsdata == NULL)
 175                 return -EPERM;
 176
 177         switch (type) {
 178         case BPF_TYPE_PROG:
 179                 return bpf_mkobj_ops(dir, dentry, mode, &bpf_prog_iops);
 180         case BPF_TYPE_MAP:
 181                 return bpf_mkobj_ops(dir, dentry, mode, &bpf_map_iops);
 182         default:
 183                 return -EPERM;
 184         }
 185 }
 186
 187 static struct dentry *
 188 bpf_lookup(struct inode *dir, struct dentry *dentry, unsigned flags)
 189 {
 190         if (strchr(dentry->d_name.name, '.'))
 191                 return ERR_PTR(-EPERM);
 192
 193         return simple_lookup(dir, dentry, flags);
 194 }
 195
 196 static int bpf_symlink(struct inode *dir, struct dentry *dentry,
 197                        const char *target)
 198 {
 199         char *link = kstrdup(target, GFP_USER | __GFP_NOWARN);
 200         struct inode *inode;
 201
 202         if (!link)
 203                 return -ENOMEM;
 204
 205         inode = bpf_get_inode(dir->i_sb, dir, S_IRWXUGO | S_IFLNK);
 206         if (IS_ERR(inode)) {
 207                 kfree(link);
 208                 return PTR_ERR(inode);
 209         }
 210
 211         inode->i_op = &simple_symlink_inode_operations;
 212         inode->i_link = link;
 213
 214         bpf_dentry_finalize(dentry, inode, dir);
 215         return 0;
 216 }
 217
 218 static const struct inode_operations bpf_dir_iops = {
 219         .lookup         = bpf_lookup,
 220         .mknod          = bpf_mkobj,
 221         .mkdir          = bpf_mkdir,
 222         .symlink        = bpf_symlink,
 223         .rmdir          = simple_rmdir,
 224         .rename         = simple_rename,
 225         .link           = simple_link,
 226         .unlink         = simple_unlink,
 227 };
 228
 229 static int bpf_obj_do_pin(const struct filename *pathname, void *raw,
 230                           enum bpf_type type)
 231 {
 232         struct dentry *dentry;
 233         struct inode *dir;
 234         struct path path;
 235         umode_t mode;
 236         dev_t devt;
 237         int ret;
 238
 239         dentry = kern_path_create(AT_FDCWD, pathname->name, &path, 0);
 240         if (IS_ERR(dentry))
 241                 return PTR_ERR(dentry);
 242
 243         mode = S_IFREG | ((S_IRUSR | S_IWUSR) & ~current_umask());
 244         devt = MKDEV(UNNAMED_MAJOR, type);
 245
 246         ret = security_path_mknod(&path, dentry, mode, devt);
 247         if (ret)
 248                 goto out;
 249
 250         dir = d_inode(path.dentry);
 251         if (dir->i_op != &bpf_dir_iops) {
 252                 ret = -EPERM;
 253                 goto out;
 254         }
 255
 256         dentry->d_fsdata = raw;
 257         ret = vfs_mknod(dir, dentry, mode, devt);
 258         dentry->d_fsdata = NULL;
 259 out:
 260         done_path_create(&path, dentry);
 261         return ret;
 262 }
 263
 264 int bpf_obj_pin_user(u32 ufd, const char __user *pathname)
 265 {
 266         struct filename *pname;
 267         enum bpf_type type;
 268         void *raw;
 269         int ret;
 270
 271         pname = getname(pathname);
 272         if (IS_ERR(pname))
 273                 return PTR_ERR(pname);
 274
 275         raw = bpf_fd_probe_obj(ufd, &type);
 276         if (IS_ERR(raw)) {
 277                 ret = PTR_ERR(raw);
 278                 goto out;
 279         }
 280
 281         ret = bpf_obj_do_pin(pname, raw, type);
 282         if (ret != 0)
 283                 bpf_any_put(raw, type);
 284 out:
 285         putname(pname);
 286         return ret;
 287 }
 288
 289 static void *bpf_obj_do_get(const struct filename *pathname,
 290                             enum bpf_type *type)
 291 {
 292         struct inode *inode;
 293         struct path path;
 294         void *raw;
 295         int ret;
 296
 297         ret = kern_path(pathname->name, LOOKUP_FOLLOW, &path);
 298         if (ret)
 299                 return ERR_PTR(ret);
 300
 301         inode = d_backing_inode(path.dentry);
 302         ret = inode_permission(inode, MAY_WRITE);
 303         if (ret)
 304                 goto out;
 305
 306         ret = bpf_inode_type(inode, type);
 307         if (ret)
 308                 goto out;
 309
 310         raw = bpf_any_get(inode->i_private, *type);
 311         if (!IS_ERR(raw))
 312                 touch_atime(&path);
 313
 314         path_put(&path);
 315         return raw;
 316 out:
 317         path_put(&path);
 318         return ERR_PTR(ret);
 319 }
 320
 321 int bpf_obj_get_user(const char __user *pathname)
 322 {
 323         enum bpf_type type = BPF_TYPE_UNSPEC;
 324         struct filename *pname;
 325         int ret = -ENOENT;
 326         void *raw;
 327
 328         pname = getname(pathname);
 329         if (IS_ERR(pname))
 330                 return PTR_ERR(pname);
 331
 332         raw = bpf_obj_do_get(pname, &type);
 333         if (IS_ERR(raw)) {
 334                 ret = PTR_ERR(raw);
 335                 goto out;
 336         }
 337
 338         if (type == BPF_TYPE_PROG)
 339                 ret = bpf_prog_new_fd(raw);
 340         else if (type == BPF_TYPE_MAP)
 341                 ret = bpf_map_new_fd(raw);
 342         else
 343                 goto out;
 344
 345         if (ret < 0)
 346                 bpf_any_put(raw, type);
 347 out:
 348         putname(pname);
 349         return ret;
 350 }
 351
 352 static void bpf_evict_inode(struct inode *inode)
 353 {
 354         enum bpf_type type;
 355
 356         truncate_inode_pages_final(&inode->i_data);
 357         clear_inode(inode);
 358
 359         if (S_ISLNK(inode->i_mode))
 360                 kfree(inode->i_link);
 361         if (!bpf_inode_type(inode, &type))
 362                 bpf_any_put(inode->i_private, type);
 363 }
 364
 365 static const struct super_operations bpf_super_ops = {
 366         .statfs         = simple_statfs,
 367         .drop_inode     = generic_delete_inode,
 368         .show_options   = generic_show_options,
 369         .evict_inode    = bpf_evict_inode,
 370 };
 371
 372 enum {
 373         OPT_MODE,
 374         OPT_ERR,
 375 };
 376
 377 static const match_table_t bpf_mount_tokens = {
 378         { OPT_MODE, "mode=%o" },
 379         { OPT_ERR, NULL },
 380 };
 381
 382 struct bpf_mount_opts {
 383         umode_t mode;
 384 };
 385
 386 static int bpf_parse_options(char *data, struct bpf_mount_opts *opts)
 387 {
 388         substring_t args[MAX_OPT_ARGS];
 389         int option, token;
 390         char *ptr;
 391
 392         opts->mode = S_IRWXUGO;
 393
 394         while ((ptr = strsep(&data, ",")) != NULL) {
 395                 if (!*ptr)
 396                         continue;
 397
 398                 token = match_token(ptr, bpf_mount_tokens, args);
 399                 switch (token) {
 400                 case OPT_MODE:
 401                         if (match_octal(&args[0], &option))
 402                                 return -EINVAL;
 403                         opts->mode = option & S_IALLUGO;
 404                         break;
 405                 /* We might like to report bad mount options here, but
 406                  * traditionally we've ignored all mount options, so we'd
 407                  * better continue to ignore non-existing options for bpf.
 408                  */
 409                 }
 410         }
 411
 412         return 0;
 413 }
 414
 415 static int bpf_fill_super(struct super_block *sb, void *data, int silent)
 416 {
 417         static struct tree_descr bpf_rfiles[] = { { "" } };
 418         struct bpf_mount_opts opts;
 419         struct inode *inode;
 420         int ret;
 421
 422         save_mount_options(sb, data);
 423
 424         ret = bpf_parse_options(data, &opts);
 425         if (ret)
 426                 return ret;
 427
 428         ret = simple_fill_super(sb, BPF_FS_MAGIC, bpf_rfiles);
 429         if (ret)
 430                 return ret;
 431
 432         sb->s_op = &bpf_super_ops;
 433
 434         inode = sb->s_root->d_inode;
 435         inode->i_op = &bpf_dir_iops;
 436         inode->i_mode &= ~S_IALLUGO;
 437         inode->i_mode |= S_ISVTX | opts.mode;
 438
 439         return 0;
 440 }
 441
 442 static struct dentry *bpf_mount(struct file_system_type *type, int flags,
 443                                 const char *dev_name, void *data)
 444 {
 445         return mount_nodev(type, flags, data, bpf_fill_super);
 446 }
 447
 448 static struct file_system_type bpf_fs_type = {
 449         .owner          = THIS_MODULE,
 450         .name           = "bpf",
 451         .mount          = bpf_mount,
 452         .kill_sb        = kill_litter_super,
 453 };
 454
 455 static int __init bpf_init(void)
 456 {
 457         int ret;
 458
 459         ret = sysfs_create_mount_point(fs_kobj, "bpf");
 460         if (ret)
 461                 return ret;
 462
 463         ret = register_filesystem(&bpf_fs_type);
 464         if (ret)
 465                 sysfs_remove_mount_point(fs_kobj, "bpf");
 466
 467         return ret;
 468 }
 469 fs_initcall(bpf_init);