fs/fsopen.c

   1 // SPDX-License-Identifier: GPL-2.0-or-later
   2 /* Filesystem access-by-fd.
   3  *
   4  * Copyright (C) 2017 Red Hat, Inc. All Rights Reserved.
   5  * Written by David Howells (dhowells@redhat.com)
   6  */
   7
   8 #include <linux/fs_context.h>
   9 #include <linux/fs_parser.h>
  10 #include <linux/slab.h>
  11 #include <linux/uaccess.h>
  12 #include <linux/syscalls.h>
  13 #include <linux/security.h>
  14 #include <linux/anon_inodes.h>
  15 #include <linux/namei.h>
  16 #include <linux/file.h>
  17 #include <uapi/linux/mount.h>
  18 #include "internal.h"
  19 #include "mount.h"
  20
  21 /*
  22  * Allow the user to read back any error, warning or informational messages.
  23  */
  24 static ssize_t fscontext_read(struct file *file,
  25                               char __user *_buf, size_t len, loff_t *pos)
  26 {
  27         struct fs_context *fc = file->private_data;
  28         struct fc_log *log = fc->log.log;
  29         unsigned int logsize = ARRAY_SIZE(log->buffer);
  30         ssize_t ret;
  31         char *p;
  32         bool need_free;
  33         int index, n;
  34
  35         ret = mutex_lock_interruptible(&fc->uapi_mutex);
  36         if (ret < 0)
  37                 return ret;
  38
  39         if (log->head == log->tail) {
  40                 mutex_unlock(&fc->uapi_mutex);
  41                 return -ENODATA;
  42         }
  43
  44         index = log->tail & (logsize - 1);
  45         p = log->buffer[index];
  46         need_free = log->need_free & (1 << index);
  47         log->buffer[index] = NULL;
  48         log->need_free &= ~(1 << index);
  49         log->tail++;
  50         mutex_unlock(&fc->uapi_mutex);
  51
  52         ret = -EMSGSIZE;
  53         n = strlen(p);
  54         if (n > len)
  55                 goto err_free;
  56         ret = -EFAULT;
  57         if (copy_to_user(_buf, p, n) != 0)
  58                 goto err_free;
  59         ret = n;
  60
  61 err_free:
  62         if (need_free)
  63                 kfree(p);
  64         return ret;
  65 }
  66
  67 static int fscontext_release(struct inode *inode, struct file *file)
  68 {
  69         struct fs_context *fc = file->private_data;
  70
  71         if (fc) {
  72                 file->private_data = NULL;
  73                 put_fs_context(fc);
  74         }
  75         return 0;
  76 }
  77
  78 const struct file_operations fscontext_fops = {
  79         .read           = fscontext_read,
  80         .release        = fscontext_release,
  81 };
  82
  83 /*
  84  * Attach a filesystem context to a file and an fd.
  85  */
  86 static int fscontext_create_fd(struct fs_context *fc, unsigned int o_flags)
  87 {
  88         int fd;
  89
  90         fd = anon_inode_getfd("[fscontext]", &fscontext_fops, fc,
  91                               O_RDWR | o_flags);
  92         if (fd < 0)
  93                 put_fs_context(fc);
  94         return fd;
  95 }
  96
  97 static int fscontext_alloc_log(struct fs_context *fc)
  98 {
  99         fc->log.log = kzalloc(sizeof(*fc->log.log), GFP_KERNEL);
 100         if (!fc->log.log)
 101                 return -ENOMEM;
 102         refcount_set(&fc->log.log->usage, 1);
 103         fc->log.log->owner = fc->fs_type->owner;
 104         return 0;
 105 }
 106
 107 /*
 108  * Open a filesystem by name so that it can be configured for mounting.
 109  *
 110  * We are allowed to specify a container in which the filesystem will be
 111  * opened, thereby indicating which namespaces will be used (notably, which
 112  * network namespace will be used for network filesystems).
 113  */
 114 SYSCALL_DEFINE2(fsopen, const char __user *, _fs_name, unsigned int, flags)
 115 {
 116         struct file_system_type *fs_type;
 117         struct fs_context *fc;
 118         const char *fs_name;
 119         int ret;
 120
 121         if (!may_mount())
 122                 return -EPERM;
 123
 124         if (flags & ~FSOPEN_CLOEXEC)
 125                 return -EINVAL;
 126
 127         fs_name = strndup_user(_fs_name, PAGE_SIZE);
 128         if (IS_ERR(fs_name))
 129                 return PTR_ERR(fs_name);
 130
 131         fs_type = get_fs_type(fs_name);
 132         kfree(fs_name);
 133         if (!fs_type)
 134                 return -ENODEV;
 135
 136         fc = fs_context_for_mount(fs_type, 0);
 137         put_filesystem(fs_type);
 138         if (IS_ERR(fc))
 139                 return PTR_ERR(fc);
 140
 141         fc->phase = FS_CONTEXT_CREATE_PARAMS;
 142
 143         ret = fscontext_alloc_log(fc);
 144         if (ret < 0)
 145                 goto err_fc;
 146
 147         return fscontext_create_fd(fc, flags & FSOPEN_CLOEXEC ? O_CLOEXEC : 0);
 148
 149 err_fc:
 150         put_fs_context(fc);
 151         return ret;
 152 }
 153
 154 /*
 155  * Pick a superblock into a context for reconfiguration.
 156  */
 157 SYSCALL_DEFINE3(fspick, int, dfd, const char __user *, path, unsigned int, flags)
 158 {
 159         struct fs_context *fc;
 160         struct path target;
 161         unsigned int lookup_flags;
 162         int ret;
 163
 164         if (!may_mount())
 165                 return -EPERM;
 166
 167         if ((flags & ~(FSPICK_CLOEXEC |
 168                        FSPICK_SYMLINK_NOFOLLOW |
 169                        FSPICK_NO_AUTOMOUNT |
 170                        FSPICK_EMPTY_PATH)) != 0)
 171                 return -EINVAL;
 172
 173         lookup_flags = LOOKUP_FOLLOW | LOOKUP_AUTOMOUNT;
 174         if (flags & FSPICK_SYMLINK_NOFOLLOW)
 175                 lookup_flags &= ~LOOKUP_FOLLOW;
 176         if (flags & FSPICK_NO_AUTOMOUNT)
 177                 lookup_flags &= ~LOOKUP_AUTOMOUNT;
 178         if (flags & FSPICK_EMPTY_PATH)
 179                 lookup_flags |= LOOKUP_EMPTY;
 180         ret = user_path_at(dfd, path, lookup_flags, &target);
 181         if (ret < 0)
 182                 goto err;
 183
 184         ret = -EINVAL;
 185         if (target.mnt->mnt_root != target.dentry)
 186                 goto err_path;
 187
 188         fc = fs_context_for_reconfigure(target.dentry, 0, 0);
 189         if (IS_ERR(fc)) {
 190                 ret = PTR_ERR(fc);
 191                 goto err_path;
 192         }
 193
 194         fc->phase = FS_CONTEXT_RECONF_PARAMS;
 195
 196         ret = fscontext_alloc_log(fc);
 197         if (ret < 0)
 198                 goto err_fc;
 199
 200         path_put(&target);
 201         return fscontext_create_fd(fc, flags & FSPICK_CLOEXEC ? O_CLOEXEC : 0);
 202
 203 err_fc:
 204         put_fs_context(fc);
 205 err_path:
 206         path_put(&target);
 207 err:
 208         return ret;
 209 }
 210
 211 static int vfs_cmd_create(struct fs_context *fc, bool exclusive)
 212 {
 213         struct super_block *sb;
 214         int ret;
 215
 216         if (fc->phase != FS_CONTEXT_CREATE_PARAMS)
 217                 return -EBUSY;
 218
 219         if (!mount_capable(fc))
 220                 return -EPERM;
 221
 222         fc->phase = FS_CONTEXT_CREATING;
 223         fc->exclusive = exclusive;
 224
 225         ret = vfs_get_tree(fc);
 226         if (ret) {
 227                 fc->phase = FS_CONTEXT_FAILED;
 228                 return ret;
 229         }
 230
 231         sb = fc->root->d_sb;
 232         ret = security_sb_kern_mount(sb);
 233         if (unlikely(ret)) {
 234                 fc_drop_locked(fc);
 235                 fc->phase = FS_CONTEXT_FAILED;
 236                 return ret;
 237         }
 238
 239         /* vfs_get_tree() callchains will have grabbed @s_umount */
 240         up_write(&sb->s_umount);
 241         fc->phase = FS_CONTEXT_AWAITING_MOUNT;
 242         return 0;
 243 }
 244
 245 static int vfs_cmd_reconfigure(struct fs_context *fc)
 246 {
 247         struct super_block *sb;
 248         int ret;
 249
 250         if (fc->phase != FS_CONTEXT_RECONF_PARAMS)
 251                 return -EBUSY;
 252
 253         fc->phase = FS_CONTEXT_RECONFIGURING;
 254
 255         sb = fc->root->d_sb;
 256         if (!ns_capable(sb->s_user_ns, CAP_SYS_ADMIN)) {
 257                 fc->phase = FS_CONTEXT_FAILED;
 258                 return -EPERM;
 259         }
 260
 261         down_write(&sb->s_umount);
 262         ret = reconfigure_super(fc);
 263         up_write(&sb->s_umount);
 264         if (ret) {
 265                 fc->phase = FS_CONTEXT_FAILED;
 266                 return ret;
 267         }
 268
 269         vfs_clean_context(fc);
 270         return 0;
 271 }
 272
 273 /*
 274  * Check the state and apply the configuration.  Note that this function is
 275  * allowed to 'steal' the value by setting param->xxx to NULL before returning.
 276  */
 277 static int vfs_fsconfig_locked(struct fs_context *fc, int cmd,
 278                                struct fs_parameter *param)
 279 {
 280         int ret;
 281
 282         ret = finish_clean_context(fc);
 283         if (ret)
 284                 return ret;
 285         switch (cmd) {
 286         case FSCONFIG_CMD_CREATE:
 287                 return vfs_cmd_create(fc, false);
 288         case FSCONFIG_CMD_CREATE_EXCL:
 289                 return vfs_cmd_create(fc, true);
 290         case FSCONFIG_CMD_RECONFIGURE:
 291                 return vfs_cmd_reconfigure(fc);
 292         default:
 293                 if (fc->phase != FS_CONTEXT_CREATE_PARAMS &&
 294                     fc->phase != FS_CONTEXT_RECONF_PARAMS)
 295                         return -EBUSY;
 296
 297                 return vfs_parse_fs_param(fc, param);
 298         }
 299 }
 300
 301 /**
 302  * sys_fsconfig - Set parameters and trigger actions on a context
 303  * @fd: The filesystem context to act upon
 304  * @cmd: The action to take
 305  * @_key: Where appropriate, the parameter key to set
 306  * @_value: Where appropriate, the parameter value to set
 307  * @aux: Additional information for the value
 308  *
 309  * This system call is used to set parameters on a context, including
 310  * superblock settings, data source and security labelling.
 311  *
 312  * Actions include triggering the creation of a superblock and the
 313  * reconfiguration of the superblock attached to the specified context.
 314  *
 315  * When setting a parameter, @cmd indicates the type of value being proposed
 316  * and @_key indicates the parameter to be altered.
 317  *
 318  * @_value and @aux are used to specify the value, should a value be required:
 319  *
 320  * (*) fsconfig_set_flag: No value is specified.  The parameter must be boolean
 321  *     in nature.  The key may be prefixed with "no" to invert the
 322  *     setting. @_value must be NULL and @aux must be 0.
 323  *
 324  * (*) fsconfig_set_string: A string value is specified.  The parameter can be
 325  *     expecting boolean, integer, string or take a path.  A conversion to an
 326  *     appropriate type will be attempted (which may include looking up as a
 327  *     path).  @_value points to a NUL-terminated string and @aux must be 0.
 328  *
 329  * (*) fsconfig_set_binary: A binary blob is specified.  @_value points to the
 330  *     blob and @aux indicates its size.  The parameter must be expecting a
 331  *     blob.
 332  *
 333  * (*) fsconfig_set_path: A non-empty path is specified.  The parameter must be
 334  *     expecting a path object.  @_value points to a NUL-terminated string that
 335  *     is the path and @aux is a file descriptor at which to start a relative
 336  *     lookup or AT_FDCWD.
 337  *
 338  * (*) fsconfig_set_path_empty: As fsconfig_set_path, but with AT_EMPTY_PATH
 339  *     implied.
 340  *
 341  * (*) fsconfig_set_fd: An open file descriptor is specified.  @_value must be
 342  *     NULL and @aux indicates the file descriptor.
 343  */
 344 SYSCALL_DEFINE5(fsconfig,
 345                 int, fd,
 346                 unsigned int, cmd,
 347                 const char __user *, _key,
 348                 const void __user *, _value,
 349                 int, aux)
 350 {
 351         struct fs_context *fc;
 352         int ret;
 353         int lookup_flags = 0;
 354
 355         struct fs_parameter param = {
 356                 .type   = fs_value_is_undefined,
 357         };
 358
 359         if (fd < 0)
 360                 return -EINVAL;
 361
 362         switch (cmd) {
 363         case FSCONFIG_SET_FLAG:
 364                 if (!_key || _value || aux)
 365                         return -EINVAL;
 366                 break;
 367         case FSCONFIG_SET_STRING:
 368                 if (!_key || !_value || aux)
 369                         return -EINVAL;
 370                 break;
 371         case FSCONFIG_SET_BINARY:
 372                 if (!_key || !_value || aux <= 0 || aux > 1024 * 1024)
 373                         return -EINVAL;
 374                 break;
 375         case FSCONFIG_SET_PATH:
 376         case FSCONFIG_SET_PATH_EMPTY:
 377                 if (!_key || !_value || (aux != AT_FDCWD && aux < 0))
 378                         return -EINVAL;
 379                 break;
 380         case FSCONFIG_SET_FD:
 381                 if (!_key || _value || aux < 0)
 382                         return -EINVAL;
 383                 break;
 384         case FSCONFIG_CMD_CREATE:
 385         case FSCONFIG_CMD_CREATE_EXCL:
 386         case FSCONFIG_CMD_RECONFIGURE:
 387                 if (_key || _value || aux)
 388                         return -EINVAL;
 389                 break;
 390         default:
 391                 return -EOPNOTSUPP;
 392         }
 393
 394         CLASS(fd, f)(fd);
 395         if (fd_empty(f))
 396                 return -EBADF;
 397         if (fd_file(f)->f_op != &fscontext_fops)
 398                 return -EINVAL;
 399
 400         fc = fd_file(f)->private_data;
 401         if (fc->ops == &legacy_fs_context_ops) {
 402                 switch (cmd) {
 403                 case FSCONFIG_SET_BINARY:
 404                 case FSCONFIG_SET_PATH:
 405                 case FSCONFIG_SET_PATH_EMPTY:
 406                 case FSCONFIG_SET_FD:
 407                 case FSCONFIG_CMD_CREATE_EXCL:
 408                         return -EOPNOTSUPP;
 409                 }
 410         }
 411
 412         if (_key) {
 413                 param.key = strndup_user(_key, 256);
 414                 if (IS_ERR(param.key))
 415                         return PTR_ERR(param.key);
 416         }
 417
 418         switch (cmd) {
 419         case FSCONFIG_SET_FLAG:
 420                 param.type = fs_value_is_flag;
 421                 break;
 422         case FSCONFIG_SET_STRING:
 423                 param.type = fs_value_is_string;
 424                 param.string = strndup_user(_value, 256);
 425                 if (IS_ERR(param.string)) {
 426                         ret = PTR_ERR(param.string);
 427                         goto out_key;
 428                 }
 429                 param.size = strlen(param.string);
 430                 break;
 431         case FSCONFIG_SET_BINARY:
 432                 param.type = fs_value_is_blob;
 433                 param.size = aux;
 434                 param.blob = memdup_user_nul(_value, aux);
 435                 if (IS_ERR(param.blob)) {
 436                         ret = PTR_ERR(param.blob);
 437                         goto out_key;
 438                 }
 439                 break;
 440         case FSCONFIG_SET_PATH_EMPTY:
 441                 lookup_flags = LOOKUP_EMPTY;
 442                 fallthrough;
 443         case FSCONFIG_SET_PATH:
 444                 param.type = fs_value_is_filename;
 445                 param.name = getname_flags(_value, lookup_flags);
 446                 if (IS_ERR(param.name)) {
 447                         ret = PTR_ERR(param.name);
 448                         goto out_key;
 449                 }
 450                 param.dirfd = aux;
 451                 param.size = strlen(param.name->name);
 452                 break;
 453         case FSCONFIG_SET_FD:
 454                 param.type = fs_value_is_file;
 455                 ret = -EBADF;
 456                 param.file = fget(aux);
 457                 if (!param.file)
 458                         goto out_key;
 459                 param.dirfd = aux;
 460                 break;
 461         default:
 462                 break;
 463         }
 464
 465         ret = mutex_lock_interruptible(&fc->uapi_mutex);
 466         if (ret == 0) {
 467                 ret = vfs_fsconfig_locked(fc, cmd, &param);
 468                 mutex_unlock(&fc->uapi_mutex);
 469         }
 470
 471         /* Clean up the our record of any value that we obtained from
 472          * userspace.  Note that the value may have been stolen by the LSM or
 473          * filesystem, in which case the value pointer will have been cleared.
 474          */
 475         switch (cmd) {
 476         case FSCONFIG_SET_STRING:
 477         case FSCONFIG_SET_BINARY:
 478                 kfree(param.string);
 479                 break;
 480         case FSCONFIG_SET_PATH:
 481         case FSCONFIG_SET_PATH_EMPTY:
 482                 if (param.name)
 483                         putname(param.name);
 484                 break;
 485         case FSCONFIG_SET_FD:
 486                 if (param.file)
 487                         fput(param.file);
 488                 break;
 489         default:
 490                 break;
 491         }
 492 out_key:
 493         kfree(param.key);
 494         return ret;
 495 }