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 (dentry->d_flags & DCACHE_NOKEY_NAME) 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 ((old_dentry->d_flags | new_dentry->d_flags) & DCACHE_NOKEY_NAME) 90 return -ENOKEY; 91 92 if (old_dir != new_dir) { 93 if (IS_ENCRYPTED(new_dir) && 94 !fscrypt_has_permitted_context(new_dir, 95 d_inode(old_dentry))) 96 return -EXDEV; 97 98 if ((flags & RENAME_EXCHANGE) && 99 IS_ENCRYPTED(old_dir) && 100 !fscrypt_has_permitted_context(old_dir, 101 d_inode(new_dentry))) 102 return -EXDEV; 103 } 104 return 0; 105 } 106 EXPORT_SYMBOL_GPL(__fscrypt_prepare_rename); 107 108 int __fscrypt_prepare_lookup(struct inode *dir, struct dentry *dentry, 109 struct fscrypt_name *fname) 110 { 111 int err = fscrypt_setup_filename(dir, &dentry->d_name, 1, fname); 112 113 if (err && err != -ENOENT) 114 return err; 115 116 if (fname->is_nokey_name) { 117 spin_lock(&dentry->d_lock); 118 dentry->d_flags |= DCACHE_NOKEY_NAME; 119 spin_unlock(&dentry->d_lock); 120 } 121 return err; 122 } 123 EXPORT_SYMBOL_GPL(__fscrypt_prepare_lookup); 124 125 /** 126 * fscrypt_prepare_setflags() - prepare to change flags with FS_IOC_SETFLAGS 127 * @inode: the inode on which flags are being changed 128 * @oldflags: the old flags 129 * @flags: the new flags 130 * 131 * The caller should be holding i_rwsem for write. 132 * 133 * Return: 0 on success; -errno if the flags change isn't allowed or if 134 * another error occurs. 135 */ 136 int fscrypt_prepare_setflags(struct inode *inode, 137 unsigned int oldflags, unsigned int flags) 138 { 139 struct fscrypt_info *ci; 140 struct fscrypt_master_key *mk; 141 int err; 142 143 /* 144 * When the CASEFOLD flag is set on an encrypted directory, we must 145 * derive the secret key needed for the dirhash. This is only possible 146 * if the directory uses a v2 encryption policy. 147 */ 148 if (IS_ENCRYPTED(inode) && (flags & ~oldflags & FS_CASEFOLD_FL)) { 149 err = fscrypt_require_key(inode); 150 if (err) 151 return err; 152 ci = inode->i_crypt_info; 153 if (ci->ci_policy.version != FSCRYPT_POLICY_V2) 154 return -EINVAL; 155 mk = ci->ci_master_key->payload.data[0]; 156 down_read(&mk->mk_secret_sem); 157 if (is_master_key_secret_present(&mk->mk_secret)) 158 err = fscrypt_derive_dirhash_key(ci, mk); 159 else 160 err = -ENOKEY; 161 up_read(&mk->mk_secret_sem); 162 return err; 163 } 164 return 0; 165 } 166 167 /** 168 * fscrypt_prepare_symlink() - prepare to create a possibly-encrypted symlink 169 * @dir: directory in which the symlink is being created 170 * @target: plaintext symlink target 171 * @len: length of @target excluding null terminator 172 * @max_len: space the filesystem has available to store the symlink target 173 * @disk_link: (out) the on-disk symlink target being prepared 174 * 175 * This function computes the size the symlink target will require on-disk, 176 * stores it in @disk_link->len, and validates it against @max_len. An 177 * encrypted symlink may be longer than the original. 178 * 179 * Additionally, @disk_link->name is set to @target if the symlink will be 180 * unencrypted, but left NULL if the symlink will be encrypted. For encrypted 181 * symlinks, the filesystem must call fscrypt_encrypt_symlink() to create the 182 * on-disk target later. (The reason for the two-step process is that some 183 * filesystems need to know the size of the symlink target before creating the 184 * inode, e.g. to determine whether it will be a "fast" or "slow" symlink.) 185 * 186 * Return: 0 on success, -ENAMETOOLONG if the symlink target is too long, 187 * -ENOKEY if the encryption key is missing, or another -errno code if a problem 188 * occurred while setting up the encryption key. 189 */ 190 int fscrypt_prepare_symlink(struct inode *dir, const char *target, 191 unsigned int len, unsigned int max_len, 192 struct fscrypt_str *disk_link) 193 { 194 const union fscrypt_policy *policy; 195 196 /* 197 * To calculate the size of the encrypted symlink target we need to know 198 * the amount of NUL padding, which is determined by the flags set in 199 * the encryption policy which will be inherited from the directory. 200 */ 201 policy = fscrypt_policy_to_inherit(dir); 202 if (policy == NULL) { 203 /* Not encrypted */ 204 disk_link->name = (unsigned char *)target; 205 disk_link->len = len + 1; 206 if (disk_link->len > max_len) 207 return -ENAMETOOLONG; 208 return 0; 209 } 210 if (IS_ERR(policy)) 211 return PTR_ERR(policy); 212 213 /* 214 * Calculate the size of the encrypted symlink and verify it won't 215 * exceed max_len. Note that for historical reasons, encrypted symlink 216 * targets are prefixed with the ciphertext length, despite this 217 * actually being redundant with i_size. This decreases by 2 bytes the 218 * longest symlink target we can accept. 219 * 220 * We could recover 1 byte by not counting a null terminator, but 221 * counting it (even though it is meaningless for ciphertext) is simpler 222 * for now since filesystems will assume it is there and subtract it. 223 */ 224 if (!fscrypt_fname_encrypted_size(policy, len, 225 max_len - sizeof(struct fscrypt_symlink_data), 226 &disk_link->len)) 227 return -ENAMETOOLONG; 228 disk_link->len += sizeof(struct fscrypt_symlink_data); 229 230 disk_link->name = NULL; 231 return 0; 232 } 233 EXPORT_SYMBOL_GPL(fscrypt_prepare_symlink); 234 235 int __fscrypt_encrypt_symlink(struct inode *inode, const char *target, 236 unsigned int len, struct fscrypt_str *disk_link) 237 { 238 int err; 239 struct qstr iname = QSTR_INIT(target, len); 240 struct fscrypt_symlink_data *sd; 241 unsigned int ciphertext_len; 242 243 /* 244 * fscrypt_prepare_new_inode() should have already set up the new 245 * symlink inode's encryption key. We don't wait until now to do it, 246 * since we may be in a filesystem transaction now. 247 */ 248 if (WARN_ON_ONCE(!fscrypt_has_encryption_key(inode))) 249 return -ENOKEY; 250 251 if (disk_link->name) { 252 /* filesystem-provided buffer */ 253 sd = (struct fscrypt_symlink_data *)disk_link->name; 254 } else { 255 sd = kmalloc(disk_link->len, GFP_NOFS); 256 if (!sd) 257 return -ENOMEM; 258 } 259 ciphertext_len = disk_link->len - sizeof(*sd); 260 sd->len = cpu_to_le16(ciphertext_len); 261 262 err = fscrypt_fname_encrypt(inode, &iname, sd->encrypted_path, 263 ciphertext_len); 264 if (err) 265 goto err_free_sd; 266 267 /* 268 * Null-terminating the ciphertext doesn't make sense, but we still 269 * count the null terminator in the length, so we might as well 270 * initialize it just in case the filesystem writes it out. 271 */ 272 sd->encrypted_path[ciphertext_len] = '\0'; 273 274 /* Cache the plaintext symlink target for later use by get_link() */ 275 err = -ENOMEM; 276 inode->i_link = kmemdup(target, len + 1, GFP_NOFS); 277 if (!inode->i_link) 278 goto err_free_sd; 279 280 if (!disk_link->name) 281 disk_link->name = (unsigned char *)sd; 282 return 0; 283 284 err_free_sd: 285 if (!disk_link->name) 286 kfree(sd); 287 return err; 288 } 289 EXPORT_SYMBOL_GPL(__fscrypt_encrypt_symlink); 290 291 /** 292 * fscrypt_get_symlink() - get the target of an encrypted symlink 293 * @inode: the symlink inode 294 * @caddr: the on-disk contents of the symlink 295 * @max_size: size of @caddr buffer 296 * @done: if successful, will be set up to free the returned target if needed 297 * 298 * If the symlink's encryption key is available, we decrypt its target. 299 * Otherwise, we encode its target for presentation. 300 * 301 * This may sleep, so the filesystem must have dropped out of RCU mode already. 302 * 303 * Return: the presentable symlink target or an ERR_PTR() 304 */ 305 const char *fscrypt_get_symlink(struct inode *inode, const void *caddr, 306 unsigned int max_size, 307 struct delayed_call *done) 308 { 309 const struct fscrypt_symlink_data *sd; 310 struct fscrypt_str cstr, pstr; 311 bool has_key; 312 int err; 313 314 /* This is for encrypted symlinks only */ 315 if (WARN_ON(!IS_ENCRYPTED(inode))) 316 return ERR_PTR(-EINVAL); 317 318 /* If the decrypted target is already cached, just return it. */ 319 pstr.name = READ_ONCE(inode->i_link); 320 if (pstr.name) 321 return pstr.name; 322 323 /* 324 * Try to set up the symlink's encryption key, but we can continue 325 * regardless of whether the key is available or not. 326 */ 327 err = fscrypt_get_encryption_info(inode); 328 if (err) 329 return ERR_PTR(err); 330 has_key = fscrypt_has_encryption_key(inode); 331 332 /* 333 * For historical reasons, encrypted symlink targets are prefixed with 334 * the ciphertext length, even though this is redundant with i_size. 335 */ 336 337 if (max_size < sizeof(*sd)) 338 return ERR_PTR(-EUCLEAN); 339 sd = caddr; 340 cstr.name = (unsigned char *)sd->encrypted_path; 341 cstr.len = le16_to_cpu(sd->len); 342 343 if (cstr.len == 0) 344 return ERR_PTR(-EUCLEAN); 345 346 if (cstr.len + sizeof(*sd) - 1 > max_size) 347 return ERR_PTR(-EUCLEAN); 348 349 err = fscrypt_fname_alloc_buffer(cstr.len, &pstr); 350 if (err) 351 return ERR_PTR(err); 352 353 err = fscrypt_fname_disk_to_usr(inode, 0, 0, &cstr, &pstr); 354 if (err) 355 goto err_kfree; 356 357 err = -EUCLEAN; 358 if (pstr.name[0] == '\0') 359 goto err_kfree; 360 361 pstr.name[pstr.len] = '\0'; 362 363 /* 364 * Cache decrypted symlink targets in i_link for later use. Don't cache 365 * symlink targets encoded without the key, since those become outdated 366 * once the key is added. This pairs with the READ_ONCE() above and in 367 * the VFS path lookup code. 368 */ 369 if (!has_key || 370 cmpxchg_release(&inode->i_link, NULL, pstr.name) != NULL) 371 set_delayed_call(done, kfree_link, pstr.name); 372 373 return pstr.name; 374 375 err_kfree: 376 kfree(pstr.name); 377 return ERR_PTR(err); 378 } 379 EXPORT_SYMBOL_GPL(fscrypt_get_symlink); 380