1 // SPDX-License-Identifier: GPL-2.0-only 2 /* 3 * fs/crypto/hooks.c 4 * 5 * Encryption hooks for higher-level filesystem operations. 6 */ 7 8 #include <linux/key.h> 9 10 #include "fscrypt_private.h" 11 12 /** 13 * fscrypt_file_open() - prepare to open a possibly-encrypted regular file 14 * @inode: the inode being opened 15 * @filp: the struct file being set up 16 * 17 * Currently, an encrypted regular file can only be opened if its encryption key 18 * is available; access to the raw encrypted contents is not supported. 19 * Therefore, we first set up the inode's encryption key (if not already done) 20 * and return an error if it's unavailable. 21 * 22 * We also verify that if the parent directory (from the path via which the file 23 * is being opened) is encrypted, then the inode being opened uses the same 24 * encryption policy. This is needed as part of the enforcement that all files 25 * in an encrypted directory tree use the same encryption policy, as a 26 * protection against certain types of offline attacks. Note that this check is 27 * needed even when opening an *unencrypted* file, since it's forbidden to have 28 * an unencrypted file in an encrypted directory. 29 * 30 * Return: 0 on success, -ENOKEY if the key is missing, or another -errno code 31 */ 32 int fscrypt_file_open(struct inode *inode, struct file *filp) 33 { 34 int err; 35 struct dentry *dir; 36 37 err = fscrypt_require_key(inode); 38 if (err) 39 return err; 40 41 dir = dget_parent(file_dentry(filp)); 42 if (IS_ENCRYPTED(d_inode(dir)) && 43 !fscrypt_has_permitted_context(d_inode(dir), inode)) { 44 fscrypt_warn(inode, 45 "Inconsistent encryption context (parent directory: %lu)", 46 d_inode(dir)->i_ino); 47 err = -EPERM; 48 } 49 dput(dir); 50 return err; 51 } 52 EXPORT_SYMBOL_GPL(fscrypt_file_open); 53 54 int __fscrypt_prepare_link(struct inode *inode, struct inode *dir, 55 struct dentry *dentry) 56 { 57 if (fscrypt_is_nokey_name(dentry)) 58 return -ENOKEY; 59 /* 60 * We don't need to separately check that the directory inode's key is 61 * available, as it's implied by the dentry not being a no-key name. 62 */ 63 64 if (!fscrypt_has_permitted_context(dir, inode)) 65 return -EXDEV; 66 67 return 0; 68 } 69 EXPORT_SYMBOL_GPL(__fscrypt_prepare_link); 70 71 int __fscrypt_prepare_rename(struct inode *old_dir, struct dentry *old_dentry, 72 struct inode *new_dir, struct dentry *new_dentry, 73 unsigned int flags) 74 { 75 if (fscrypt_is_nokey_name(old_dentry) || 76 fscrypt_is_nokey_name(new_dentry)) 77 return -ENOKEY; 78 /* 79 * We don't need to separately check that the directory inodes' keys are 80 * available, as it's implied by the dentries not being no-key names. 81 */ 82 83 if (old_dir != new_dir) { 84 if (IS_ENCRYPTED(new_dir) && 85 !fscrypt_has_permitted_context(new_dir, 86 d_inode(old_dentry))) 87 return -EXDEV; 88 89 if ((flags & RENAME_EXCHANGE) && 90 IS_ENCRYPTED(old_dir) && 91 !fscrypt_has_permitted_context(old_dir, 92 d_inode(new_dentry))) 93 return -EXDEV; 94 } 95 return 0; 96 } 97 EXPORT_SYMBOL_GPL(__fscrypt_prepare_rename); 98 99 int __fscrypt_prepare_lookup(struct inode *dir, struct dentry *dentry, 100 struct fscrypt_name *fname) 101 { 102 int err = fscrypt_setup_filename(dir, &dentry->d_name, 1, fname); 103 104 if (err && err != -ENOENT) 105 return err; 106 107 if (fname->is_nokey_name) { 108 spin_lock(&dentry->d_lock); 109 dentry->d_flags |= DCACHE_NOKEY_NAME; 110 spin_unlock(&dentry->d_lock); 111 } 112 return err; 113 } 114 EXPORT_SYMBOL_GPL(__fscrypt_prepare_lookup); 115 116 int __fscrypt_prepare_readdir(struct inode *dir) 117 { 118 return fscrypt_get_encryption_info(dir, true); 119 } 120 EXPORT_SYMBOL_GPL(__fscrypt_prepare_readdir); 121 122 int __fscrypt_prepare_setattr(struct dentry *dentry, struct iattr *attr) 123 { 124 if (attr->ia_valid & ATTR_SIZE) 125 return fscrypt_require_key(d_inode(dentry)); 126 return 0; 127 } 128 EXPORT_SYMBOL_GPL(__fscrypt_prepare_setattr); 129 130 /** 131 * fscrypt_prepare_setflags() - prepare to change flags with FS_IOC_SETFLAGS 132 * @inode: the inode on which flags are being changed 133 * @oldflags: the old flags 134 * @flags: the new flags 135 * 136 * The caller should be holding i_rwsem for write. 137 * 138 * Return: 0 on success; -errno if the flags change isn't allowed or if 139 * another error occurs. 140 */ 141 int fscrypt_prepare_setflags(struct inode *inode, 142 unsigned int oldflags, unsigned int flags) 143 { 144 struct fscrypt_info *ci; 145 struct key *key; 146 struct fscrypt_master_key *mk; 147 int err; 148 149 /* 150 * When the CASEFOLD flag is set on an encrypted directory, we must 151 * derive the secret key needed for the dirhash. This is only possible 152 * if the directory uses a v2 encryption policy. 153 */ 154 if (IS_ENCRYPTED(inode) && (flags & ~oldflags & FS_CASEFOLD_FL)) { 155 err = fscrypt_require_key(inode); 156 if (err) 157 return err; 158 ci = inode->i_crypt_info; 159 if (ci->ci_policy.version != FSCRYPT_POLICY_V2) 160 return -EINVAL; 161 key = ci->ci_master_key; 162 mk = key->payload.data[0]; 163 down_read(&key->sem); 164 if (is_master_key_secret_present(&mk->mk_secret)) 165 err = fscrypt_derive_dirhash_key(ci, mk); 166 else 167 err = -ENOKEY; 168 up_read(&key->sem); 169 return err; 170 } 171 return 0; 172 } 173 174 /** 175 * fscrypt_prepare_symlink() - prepare to create a possibly-encrypted symlink 176 * @dir: directory in which the symlink is being created 177 * @target: plaintext symlink target 178 * @len: length of @target excluding null terminator 179 * @max_len: space the filesystem has available to store the symlink target 180 * @disk_link: (out) the on-disk symlink target being prepared 181 * 182 * This function computes the size the symlink target will require on-disk, 183 * stores it in @disk_link->len, and validates it against @max_len. An 184 * encrypted symlink may be longer than the original. 185 * 186 * Additionally, @disk_link->name is set to @target if the symlink will be 187 * unencrypted, but left NULL if the symlink will be encrypted. For encrypted 188 * symlinks, the filesystem must call fscrypt_encrypt_symlink() to create the 189 * on-disk target later. (The reason for the two-step process is that some 190 * filesystems need to know the size of the symlink target before creating the 191 * inode, e.g. to determine whether it will be a "fast" or "slow" symlink.) 192 * 193 * Return: 0 on success, -ENAMETOOLONG if the symlink target is too long, 194 * -ENOKEY if the encryption key is missing, or another -errno code if a problem 195 * occurred while setting up the encryption key. 196 */ 197 int fscrypt_prepare_symlink(struct inode *dir, const char *target, 198 unsigned int len, unsigned int max_len, 199 struct fscrypt_str *disk_link) 200 { 201 const union fscrypt_policy *policy; 202 203 /* 204 * To calculate the size of the encrypted symlink target we need to know 205 * the amount of NUL padding, which is determined by the flags set in 206 * the encryption policy which will be inherited from the directory. 207 */ 208 policy = fscrypt_policy_to_inherit(dir); 209 if (policy == NULL) { 210 /* Not encrypted */ 211 disk_link->name = (unsigned char *)target; 212 disk_link->len = len + 1; 213 if (disk_link->len > max_len) 214 return -ENAMETOOLONG; 215 return 0; 216 } 217 if (IS_ERR(policy)) 218 return PTR_ERR(policy); 219 220 /* 221 * Calculate the size of the encrypted symlink and verify it won't 222 * exceed max_len. Note that for historical reasons, encrypted symlink 223 * targets are prefixed with the ciphertext length, despite this 224 * actually being redundant with i_size. This decreases by 2 bytes the 225 * longest symlink target we can accept. 226 * 227 * We could recover 1 byte by not counting a null terminator, but 228 * counting it (even though it is meaningless for ciphertext) is simpler 229 * for now since filesystems will assume it is there and subtract it. 230 */ 231 if (!fscrypt_fname_encrypted_size(policy, len, 232 max_len - sizeof(struct fscrypt_symlink_data), 233 &disk_link->len)) 234 return -ENAMETOOLONG; 235 disk_link->len += sizeof(struct fscrypt_symlink_data); 236 237 disk_link->name = NULL; 238 return 0; 239 } 240 EXPORT_SYMBOL_GPL(fscrypt_prepare_symlink); 241 242 int __fscrypt_encrypt_symlink(struct inode *inode, const char *target, 243 unsigned int len, struct fscrypt_str *disk_link) 244 { 245 int err; 246 struct qstr iname = QSTR_INIT(target, len); 247 struct fscrypt_symlink_data *sd; 248 unsigned int ciphertext_len; 249 250 /* 251 * fscrypt_prepare_new_inode() should have already set up the new 252 * symlink inode's encryption key. We don't wait until now to do it, 253 * since we may be in a filesystem transaction now. 254 */ 255 if (WARN_ON_ONCE(!fscrypt_has_encryption_key(inode))) 256 return -ENOKEY; 257 258 if (disk_link->name) { 259 /* filesystem-provided buffer */ 260 sd = (struct fscrypt_symlink_data *)disk_link->name; 261 } else { 262 sd = kmalloc(disk_link->len, GFP_NOFS); 263 if (!sd) 264 return -ENOMEM; 265 } 266 ciphertext_len = disk_link->len - sizeof(*sd); 267 sd->len = cpu_to_le16(ciphertext_len); 268 269 err = fscrypt_fname_encrypt(inode, &iname, sd->encrypted_path, 270 ciphertext_len); 271 if (err) 272 goto err_free_sd; 273 274 /* 275 * Null-terminating the ciphertext doesn't make sense, but we still 276 * count the null terminator in the length, so we might as well 277 * initialize it just in case the filesystem writes it out. 278 */ 279 sd->encrypted_path[ciphertext_len] = '\0'; 280 281 /* Cache the plaintext symlink target for later use by get_link() */ 282 err = -ENOMEM; 283 inode->i_link = kmemdup(target, len + 1, GFP_NOFS); 284 if (!inode->i_link) 285 goto err_free_sd; 286 287 if (!disk_link->name) 288 disk_link->name = (unsigned char *)sd; 289 return 0; 290 291 err_free_sd: 292 if (!disk_link->name) 293 kfree(sd); 294 return err; 295 } 296 EXPORT_SYMBOL_GPL(__fscrypt_encrypt_symlink); 297 298 /** 299 * fscrypt_get_symlink() - get the target of an encrypted symlink 300 * @inode: the symlink inode 301 * @caddr: the on-disk contents of the symlink 302 * @max_size: size of @caddr buffer 303 * @done: if successful, will be set up to free the returned target if needed 304 * 305 * If the symlink's encryption key is available, we decrypt its target. 306 * Otherwise, we encode its target for presentation. 307 * 308 * This may sleep, so the filesystem must have dropped out of RCU mode already. 309 * 310 * Return: the presentable symlink target or an ERR_PTR() 311 */ 312 const char *fscrypt_get_symlink(struct inode *inode, const void *caddr, 313 unsigned int max_size, 314 struct delayed_call *done) 315 { 316 const struct fscrypt_symlink_data *sd; 317 struct fscrypt_str cstr, pstr; 318 bool has_key; 319 int err; 320 321 /* This is for encrypted symlinks only */ 322 if (WARN_ON(!IS_ENCRYPTED(inode))) 323 return ERR_PTR(-EINVAL); 324 325 /* If the decrypted target is already cached, just return it. */ 326 pstr.name = READ_ONCE(inode->i_link); 327 if (pstr.name) 328 return pstr.name; 329 330 /* 331 * Try to set up the symlink's encryption key, but we can continue 332 * regardless of whether the key is available or not. 333 */ 334 err = fscrypt_get_encryption_info(inode, false); 335 if (err) 336 return ERR_PTR(err); 337 has_key = fscrypt_has_encryption_key(inode); 338 339 /* 340 * For historical reasons, encrypted symlink targets are prefixed with 341 * the ciphertext length, even though this is redundant with i_size. 342 */ 343 344 if (max_size < sizeof(*sd)) 345 return ERR_PTR(-EUCLEAN); 346 sd = caddr; 347 cstr.name = (unsigned char *)sd->encrypted_path; 348 cstr.len = le16_to_cpu(sd->len); 349 350 if (cstr.len == 0) 351 return ERR_PTR(-EUCLEAN); 352 353 if (cstr.len + sizeof(*sd) - 1 > max_size) 354 return ERR_PTR(-EUCLEAN); 355 356 err = fscrypt_fname_alloc_buffer(cstr.len, &pstr); 357 if (err) 358 return ERR_PTR(err); 359 360 err = fscrypt_fname_disk_to_usr(inode, 0, 0, &cstr, &pstr); 361 if (err) 362 goto err_kfree; 363 364 err = -EUCLEAN; 365 if (pstr.name[0] == '\0') 366 goto err_kfree; 367 368 pstr.name[pstr.len] = '\0'; 369 370 /* 371 * Cache decrypted symlink targets in i_link for later use. Don't cache 372 * symlink targets encoded without the key, since those become outdated 373 * once the key is added. This pairs with the READ_ONCE() above and in 374 * the VFS path lookup code. 375 */ 376 if (!has_key || 377 cmpxchg_release(&inode->i_link, NULL, pstr.name) != NULL) 378 set_delayed_call(done, kfree_link, pstr.name); 379 380 return pstr.name; 381 382 err_kfree: 383 kfree(pstr.name); 384 return ERR_PTR(err); 385 } 386 EXPORT_SYMBOL_GPL(fscrypt_get_symlink); 387