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         .llseek         = no_llseek,
  82 };
  83
  84 /*
  85  * Attach a filesystem context to a file and an fd.
  86  */
  87 static int fscontext_create_fd(struct fs_context *fc, unsigned int o_flags)
  88 {
  89         int fd;
  90
  91         fd = anon_inode_getfd("[fscontext]", &fscontext_fops, fc,
  92                               O_RDWR | o_flags);
  93         if (fd < 0)
  94                 put_fs_context(fc);
  95         return fd;
  96 }
  97
  98 static int fscontext_alloc_log(struct fs_context *fc)
  99 {
 100         fc->log.log = kzalloc(sizeof(*fc->log.log), GFP_KERNEL);
 101         if (!fc->log.log)
 102                 return -ENOMEM;
 103         refcount_set(&fc->log.log->usage, 1);
 104         fc->log.log->owner = fc->fs_type->owner;
 105         return 0;
 106 }
 107
 108 /*
 109  * Open a filesystem by name so that it can be configured for mounting.
 110  *
 111  * We are allowed to specify a container in which the filesystem will be
 112  * opened, thereby indicating which namespaces will be used (notably, which
 113  * network namespace will be used for network filesystems).
 114  */
 115 SYSCALL_DEFINE2(fsopen, const char __user *, _fs_name, unsigned int, flags)
 116 {
 117         struct file_system_type *fs_type;
 118         struct fs_context *fc;
 119         const char *fs_name;
 120         int ret;
 121
 122         if (!ns_capable(current->nsproxy->mnt_ns->user_ns, CAP_SYS_ADMIN))
 123                 return -EPERM;
 124
 125         if (flags & ~FSOPEN_CLOEXEC)
 126                 return -EINVAL;
 127
 128         fs_name = strndup_user(_fs_name, PAGE_SIZE);
 129         if (IS_ERR(fs_name))
 130                 return PTR_ERR(fs_name);
 131
 132         fs_type = get_fs_type(fs_name);
 133         kfree(fs_name);
 134         if (!fs_type)
 135                 return -ENODEV;
 136
 137         fc = fs_context_for_mount(fs_type, 0);
 138         put_filesystem(fs_type);
 139         if (IS_ERR(fc))
 140                 return PTR_ERR(fc);
 141
 142         fc->phase = FS_CONTEXT_CREATE_PARAMS;
 143
 144         ret = fscontext_alloc_log(fc);
 145         if (ret < 0)
 146                 goto err_fc;
 147
 148         return fscontext_create_fd(fc, flags & FSOPEN_CLOEXEC ? O_CLOEXEC : 0);
 149
 150 err_fc:
 151         put_fs_context(fc);
 152         return ret;
 153 }
 154
 155 /*
 156  * Pick a superblock into a context for reconfiguration.
 157  */
 158 SYSCALL_DEFINE3(fspick, int, dfd, const char __user *, path, unsigned int, flags)
 159 {
 160         struct fs_context *fc;
 161         struct path target;
 162         unsigned int lookup_flags;
 163         int ret;
 164
 165         if (!ns_capable(current->nsproxy->mnt_ns->user_ns, CAP_SYS_ADMIN))
 166                 return -EPERM;
 167
 168         if ((flags & ~(FSPICK_CLOEXEC |
 169                        FSPICK_SYMLINK_NOFOLLOW |
 170                        FSPICK_NO_AUTOMOUNT |
 171                        FSPICK_EMPTY_PATH)) != 0)
 172                 return -EINVAL;
 173
 174         lookup_flags = LOOKUP_FOLLOW | LOOKUP_AUTOMOUNT;
 175         if (flags & FSPICK_SYMLINK_NOFOLLOW)
 176                 lookup_flags &= ~LOOKUP_FOLLOW;
 177         if (flags & FSPICK_NO_AUTOMOUNT)
 178                 lookup_flags &= ~LOOKUP_AUTOMOUNT;
 179         if (flags & FSPICK_EMPTY_PATH)
 180                 lookup_flags |= LOOKUP_EMPTY;
 181         ret = user_path_at(dfd, path, lookup_flags, &target);
 182         if (ret < 0)
 183                 goto err;
 184
 185         ret = -EINVAL;
 186         if (target.mnt->mnt_root != target.dentry)
 187                 goto err_path;
 188
 189         fc = fs_context_for_reconfigure(target.dentry, 0, 0);
 190         if (IS_ERR(fc)) {
 191                 ret = PTR_ERR(fc);
 192                 goto err_path;
 193         }
 194
 195         fc->phase = FS_CONTEXT_RECONF_PARAMS;
 196
 197         ret = fscontext_alloc_log(fc);
 198         if (ret < 0)
 199                 goto err_fc;
 200
 201         path_put(&target);
 202         return fscontext_create_fd(fc, flags & FSPICK_CLOEXEC ? O_CLOEXEC : 0);
 203
 204 err_fc:
 205         put_fs_context(fc);
 206 err_path:
 207         path_put(&target);
 208 err:
 209         return ret;
 210 }
 211
 212 /*
 213  * Check the state and apply the configuration.  Note that this function is
 214  * allowed to 'steal' the value by setting param->xxx to NULL before returning.
 215  */
 216 static int vfs_fsconfig_locked(struct fs_context *fc, int cmd,
 217                                struct fs_parameter *param)
 218 {
 219         struct super_block *sb;
 220         int ret;
 221
 222         ret = finish_clean_context(fc);
 223         if (ret)
 224                 return ret;
 225         switch (cmd) {
 226         case FSCONFIG_CMD_CREATE:
 227                 if (fc->phase != FS_CONTEXT_CREATE_PARAMS)
 228                         return -EBUSY;
 229                 if (!mount_capable(fc))
 230                         return -EPERM;
 231                 fc->phase = FS_CONTEXT_CREATING;
 232                 ret = vfs_get_tree(fc);
 233                 if (ret)
 234                         break;
 235                 sb = fc->root->d_sb;
 236                 ret = security_sb_kern_mount(sb);
 237                 if (unlikely(ret)) {
 238                         fc_drop_locked(fc);
 239                         break;
 240                 }
 241                 up_write(&sb->s_umount);
 242                 fc->phase = FS_CONTEXT_AWAITING_MOUNT;
 243                 return 0;
 244         case FSCONFIG_CMD_RECONFIGURE:
 245                 if (fc->phase != FS_CONTEXT_RECONF_PARAMS)
 246                         return -EBUSY;
 247                 fc->phase = FS_CONTEXT_RECONFIGURING;
 248                 sb = fc->root->d_sb;
 249                 if (!ns_capable(sb->s_user_ns, CAP_SYS_ADMIN)) {
 250                         ret = -EPERM;
 251                         break;
 252                 }
 253                 down_write(&sb->s_umount);
 254                 ret = reconfigure_super(fc);
 255                 up_write(&sb->s_umount);
 256                 if (ret)
 257                         break;
 258                 vfs_clean_context(fc);
 259                 return 0;
 260         default:
 261                 if (fc->phase != FS_CONTEXT_CREATE_PARAMS &&
 262                     fc->phase != FS_CONTEXT_RECONF_PARAMS)
 263                         return -EBUSY;
 264
 265                 return vfs_parse_fs_param(fc, param);
 266         }
 267         fc->phase = FS_CONTEXT_FAILED;
 268         return ret;
 269 }
 270
 271 /**
 272  * sys_fsconfig - Set parameters and trigger actions on a context
 273  * @fd: The filesystem context to act upon
 274  * @cmd: The action to take
 275  * @_key: Where appropriate, the parameter key to set
 276  * @_value: Where appropriate, the parameter value to set
 277  * @aux: Additional information for the value
 278  *
 279  * This system call is used to set parameters on a context, including
 280  * superblock settings, data source and security labelling.
 281  *
 282  * Actions include triggering the creation of a superblock and the
 283  * reconfiguration of the superblock attached to the specified context.
 284  *
 285  * When setting a parameter, @cmd indicates the type of value being proposed
 286  * and @_key indicates the parameter to be altered.
 287  *
 288  * @_value and @aux are used to specify the value, should a value be required:
 289  *
 290  * (*) fsconfig_set_flag: No value is specified.  The parameter must be boolean
 291  *     in nature.  The key may be prefixed with "no" to invert the
 292  *     setting. @_value must be NULL and @aux must be 0.
 293  *
 294  * (*) fsconfig_set_string: A string value is specified.  The parameter can be
 295  *     expecting boolean, integer, string or take a path.  A conversion to an
 296  *     appropriate type will be attempted (which may include looking up as a
 297  *     path).  @_value points to a NUL-terminated string and @aux must be 0.
 298  *
 299  * (*) fsconfig_set_binary: A binary blob is specified.  @_value points to the
 300  *     blob and @aux indicates its size.  The parameter must be expecting a
 301  *     blob.
 302  *
 303  * (*) fsconfig_set_path: A non-empty path is specified.  The parameter must be
 304  *     expecting a path object.  @_value points to a NUL-terminated string that
 305  *     is the path and @aux is a file descriptor at which to start a relative
 306  *     lookup or AT_FDCWD.
 307  *
 308  * (*) fsconfig_set_path_empty: As fsconfig_set_path, but with AT_EMPTY_PATH
 309  *     implied.
 310  *
 311  * (*) fsconfig_set_fd: An open file descriptor is specified.  @_value must be
 312  *     NULL and @aux indicates the file descriptor.
 313  */
 314 SYSCALL_DEFINE5(fsconfig,
 315                 int, fd,
 316                 unsigned int, cmd,
 317                 const char __user *, _key,
 318                 const void __user *, _value,
 319                 int, aux)
 320 {
 321         struct fs_context *fc;
 322         struct fd f;
 323         int ret;
 324         int lookup_flags = 0;
 325
 326         struct fs_parameter param = {
 327                 .type   = fs_value_is_undefined,
 328         };
 329
 330         if (fd < 0)
 331                 return -EINVAL;
 332
 333         switch (cmd) {
 334         case FSCONFIG_SET_FLAG:
 335                 if (!_key || _value || aux)
 336                         return -EINVAL;
 337                 break;
 338         case FSCONFIG_SET_STRING:
 339                 if (!_key || !_value || aux)
 340                         return -EINVAL;
 341                 break;
 342         case FSCONFIG_SET_BINARY:
 343                 if (!_key || !_value || aux <= 0 || aux > 1024 * 1024)
 344                         return -EINVAL;
 345                 break;
 346         case FSCONFIG_SET_PATH:
 347         case FSCONFIG_SET_PATH_EMPTY:
 348                 if (!_key || !_value || (aux != AT_FDCWD && aux < 0))
 349                         return -EINVAL;
 350                 break;
 351         case FSCONFIG_SET_FD:
 352                 if (!_key || _value || aux < 0)
 353                         return -EINVAL;
 354                 break;
 355         case FSCONFIG_CMD_CREATE:
 356         case FSCONFIG_CMD_RECONFIGURE:
 357                 if (_key || _value || aux)
 358                         return -EINVAL;
 359                 break;
 360         default:
 361                 return -EOPNOTSUPP;
 362         }
 363
 364         f = fdget(fd);
 365         if (!f.file)
 366                 return -EBADF;
 367         ret = -EINVAL;
 368         if (f.file->f_op != &fscontext_fops)
 369                 goto out_f;
 370
 371         fc = f.file->private_data;
 372         if (fc->ops == &legacy_fs_context_ops) {
 373                 switch (cmd) {
 374                 case FSCONFIG_SET_BINARY:
 375                 case FSCONFIG_SET_PATH:
 376                 case FSCONFIG_SET_PATH_EMPTY:
 377                 case FSCONFIG_SET_FD:
 378                         ret = -EOPNOTSUPP;
 379                         goto out_f;
 380                 }
 381         }
 382
 383         if (_key) {
 384                 param.key = strndup_user(_key, 256);
 385                 if (IS_ERR(param.key)) {
 386                         ret = PTR_ERR(param.key);
 387                         goto out_f;
 388                 }
 389         }
 390
 391         switch (cmd) {
 392         case FSCONFIG_SET_FLAG:
 393                 param.type = fs_value_is_flag;
 394                 break;
 395         case FSCONFIG_SET_STRING:
 396                 param.type = fs_value_is_string;
 397                 param.string = strndup_user(_value, 256);
 398                 if (IS_ERR(param.string)) {
 399                         ret = PTR_ERR(param.string);
 400                         goto out_key;
 401                 }
 402                 param.size = strlen(param.string);
 403                 break;
 404         case FSCONFIG_SET_BINARY:
 405                 param.type = fs_value_is_blob;
 406                 param.size = aux;
 407                 param.blob = memdup_user_nul(_value, aux);
 408                 if (IS_ERR(param.blob)) {
 409                         ret = PTR_ERR(param.blob);
 410                         goto out_key;
 411                 }
 412                 break;
 413         case FSCONFIG_SET_PATH_EMPTY:
 414                 lookup_flags = LOOKUP_EMPTY;
 415                 /* fallthru */
 416         case FSCONFIG_SET_PATH:
 417                 param.type = fs_value_is_filename;
 418                 param.name = getname_flags(_value, lookup_flags, NULL);
 419                 if (IS_ERR(param.name)) {
 420                         ret = PTR_ERR(param.name);
 421                         goto out_key;
 422                 }
 423                 param.dirfd = aux;
 424                 param.size = strlen(param.name->name);
 425                 break;
 426         case FSCONFIG_SET_FD:
 427                 param.type = fs_value_is_file;
 428                 ret = -EBADF;
 429                 param.file = fget(aux);
 430                 if (!param.file)
 431                         goto out_key;
 432                 break;
 433         default:
 434                 break;
 435         }
 436
 437         ret = mutex_lock_interruptible(&fc->uapi_mutex);
 438         if (ret == 0) {
 439                 ret = vfs_fsconfig_locked(fc, cmd, &param);
 440                 mutex_unlock(&fc->uapi_mutex);
 441         }
 442
 443         /* Clean up the our record of any value that we obtained from
 444          * userspace.  Note that the value may have been stolen by the LSM or
 445          * filesystem, in which case the value pointer will have been cleared.
 446          */
 447         switch (cmd) {
 448         case FSCONFIG_SET_STRING:
 449         case FSCONFIG_SET_BINARY:
 450                 kfree(param.string);
 451                 break;
 452         case FSCONFIG_SET_PATH:
 453         case FSCONFIG_SET_PATH_EMPTY:
 454                 if (param.name)
 455                         putname(param.name);
 456                 break;
 457         case FSCONFIG_SET_FD:
 458                 if (param.file)
 459                         fput(param.file);
 460                 break;
 461         default:
 462                 break;
 463         }
 464 out_key:
 465         kfree(param.key);
 466 out_f:
 467         fdput(f);
 468         return ret;
 469 }