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