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 d_set_d_op(dentry, &fscrypt_d_ops); 121 } 122 return err; 123 } 124 EXPORT_SYMBOL_GPL(__fscrypt_prepare_lookup); 125 126 /** 127 * fscrypt_prepare_setflags() - prepare to change flags with FS_IOC_SETFLAGS 128 * @inode: the inode on which flags are being changed 129 * @oldflags: the old flags 130 * @flags: the new flags 131 * 132 * The caller should be holding i_rwsem for write. 133 * 134 * Return: 0 on success; -errno if the flags change isn't allowed or if 135 * another error occurs. 136 */ 137 int fscrypt_prepare_setflags(struct inode *inode, 138 unsigned int oldflags, unsigned int flags) 139 { 140 struct fscrypt_info *ci; 141 struct fscrypt_master_key *mk; 142 int err; 143 144 /* 145 * When the CASEFOLD flag is set on an encrypted directory, we must 146 * derive the secret key needed for the dirhash. This is only possible 147 * if the directory uses a v2 encryption policy. 148 */ 149 if (IS_ENCRYPTED(inode) && (flags & ~oldflags & FS_CASEFOLD_FL)) { 150 err = fscrypt_require_key(inode); 151 if (err) 152 return err; 153 ci = inode->i_crypt_info; 154 if (ci->ci_policy.version != FSCRYPT_POLICY_V2) 155 return -EINVAL; 156 mk = ci->ci_master_key->payload.data[0]; 157 down_read(&mk->mk_secret_sem); 158 if (is_master_key_secret_present(&mk->mk_secret)) 159 err = fscrypt_derive_dirhash_key(ci, mk); 160 else 161 err = -ENOKEY; 162 up_read(&mk->mk_secret_sem); 163 return err; 164 } 165 return 0; 166 } 167 168 /** 169 * fscrypt_prepare_symlink() - prepare to create a possibly-encrypted symlink 170 * @dir: directory in which the symlink is being created 171 * @target: plaintext symlink target 172 * @len: length of @target excluding null terminator 173 * @max_len: space the filesystem has available to store the symlink target 174 * @disk_link: (out) the on-disk symlink target being prepared 175 * 176 * This function computes the size the symlink target will require on-disk, 177 * stores it in @disk_link->len, and validates it against @max_len. An 178 * encrypted symlink may be longer than the original. 179 * 180 * Additionally, @disk_link->name is set to @target if the symlink will be 181 * unencrypted, but left NULL if the symlink will be encrypted. For encrypted 182 * symlinks, the filesystem must call fscrypt_encrypt_symlink() to create the 183 * on-disk target later. (The reason for the two-step process is that some 184 * filesystems need to know the size of the symlink target before creating the 185 * inode, e.g. to determine whether it will be a "fast" or "slow" symlink.) 186 * 187 * Return: 0 on success, -ENAMETOOLONG if the symlink target is too long, 188 * -ENOKEY if the encryption key is missing, or another -errno code if a problem 189 * occurred while setting up the encryption key. 190 */ 191 int fscrypt_prepare_symlink(struct inode *dir, const char *target, 192 unsigned int len, unsigned int max_len, 193 struct fscrypt_str *disk_link) 194 { 195 const union fscrypt_policy *policy; 196 197 /* 198 * To calculate the size of the encrypted symlink target we need to know 199 * the amount of NUL padding, which is determined by the flags set in 200 * the encryption policy which will be inherited from the directory. 201 */ 202 policy = fscrypt_policy_to_inherit(dir); 203 if (policy == NULL) { 204 /* Not encrypted */ 205 disk_link->name = (unsigned char *)target; 206 disk_link->len = len + 1; 207 if (disk_link->len > max_len) 208 return -ENAMETOOLONG; 209 return 0; 210 } 211 if (IS_ERR(policy)) 212 return PTR_ERR(policy); 213 214 /* 215 * Calculate the size of the encrypted symlink and verify it won't 216 * exceed max_len. Note that for historical reasons, encrypted symlink 217 * targets are prefixed with the ciphertext length, despite this 218 * actually being redundant with i_size. This decreases by 2 bytes the 219 * longest symlink target we can accept. 220 * 221 * We could recover 1 byte by not counting a null terminator, but 222 * counting it (even though it is meaningless for ciphertext) is simpler 223 * for now since filesystems will assume it is there and subtract it. 224 */ 225 if (!fscrypt_fname_encrypted_size(policy, len, 226 max_len - sizeof(struct fscrypt_symlink_data), 227 &disk_link->len)) 228 return -ENAMETOOLONG; 229 disk_link->len += sizeof(struct fscrypt_symlink_data); 230 231 disk_link->name = NULL; 232 return 0; 233 } 234 EXPORT_SYMBOL_GPL(fscrypt_prepare_symlink); 235 236 int __fscrypt_encrypt_symlink(struct inode *inode, const char *target, 237 unsigned int len, struct fscrypt_str *disk_link) 238 { 239 int err; 240 struct qstr iname = QSTR_INIT(target, len); 241 struct fscrypt_symlink_data *sd; 242 unsigned int ciphertext_len; 243 244 /* 245 * fscrypt_prepare_new_inode() should have already set up the new 246 * symlink inode's encryption key. We don't wait until now to do it, 247 * since we may be in a filesystem transaction now. 248 */ 249 if (WARN_ON_ONCE(!fscrypt_has_encryption_key(inode))) 250 return -ENOKEY; 251 252 if (disk_link->name) { 253 /* filesystem-provided buffer */ 254 sd = (struct fscrypt_symlink_data *)disk_link->name; 255 } else { 256 sd = kmalloc(disk_link->len, GFP_NOFS); 257 if (!sd) 258 return -ENOMEM; 259 } 260 ciphertext_len = disk_link->len - sizeof(*sd); 261 sd->len = cpu_to_le16(ciphertext_len); 262 263 err = fscrypt_fname_encrypt(inode, &iname, sd->encrypted_path, 264 ciphertext_len); 265 if (err) 266 goto err_free_sd; 267 268 /* 269 * Null-terminating the ciphertext doesn't make sense, but we still 270 * count the null terminator in the length, so we might as well 271 * initialize it just in case the filesystem writes it out. 272 */ 273 sd->encrypted_path[ciphertext_len] = '\0'; 274 275 /* Cache the plaintext symlink target for later use by get_link() */ 276 err = -ENOMEM; 277 inode->i_link = kmemdup(target, len + 1, GFP_NOFS); 278 if (!inode->i_link) 279 goto err_free_sd; 280 281 if (!disk_link->name) 282 disk_link->name = (unsigned char *)sd; 283 return 0; 284 285 err_free_sd: 286 if (!disk_link->name) 287 kfree(sd); 288 return err; 289 } 290 EXPORT_SYMBOL_GPL(__fscrypt_encrypt_symlink); 291 292 /** 293 * fscrypt_get_symlink() - get the target of an encrypted symlink 294 * @inode: the symlink inode 295 * @caddr: the on-disk contents of the symlink 296 * @max_size: size of @caddr buffer 297 * @done: if successful, will be set up to free the returned target if needed 298 * 299 * If the symlink's encryption key is available, we decrypt its target. 300 * Otherwise, we encode its target for presentation. 301 * 302 * This may sleep, so the filesystem must have dropped out of RCU mode already. 303 * 304 * Return: the presentable symlink target or an ERR_PTR() 305 */ 306 const char *fscrypt_get_symlink(struct inode *inode, const void *caddr, 307 unsigned int max_size, 308 struct delayed_call *done) 309 { 310 const struct fscrypt_symlink_data *sd; 311 struct fscrypt_str cstr, pstr; 312 bool has_key; 313 int err; 314 315 /* This is for encrypted symlinks only */ 316 if (WARN_ON(!IS_ENCRYPTED(inode))) 317 return ERR_PTR(-EINVAL); 318 319 /* If the decrypted target is already cached, just return it. */ 320 pstr.name = READ_ONCE(inode->i_link); 321 if (pstr.name) 322 return pstr.name; 323 324 /* 325 * Try to set up the symlink's encryption key, but we can continue 326 * regardless of whether the key is available or not. 327 */ 328 err = fscrypt_get_encryption_info(inode); 329 if (err) 330 return ERR_PTR(err); 331 has_key = fscrypt_has_encryption_key(inode); 332 333 /* 334 * For historical reasons, encrypted symlink targets are prefixed with 335 * the ciphertext length, even though this is redundant with i_size. 336 */ 337 338 if (max_size < sizeof(*sd)) 339 return ERR_PTR(-EUCLEAN); 340 sd = caddr; 341 cstr.name = (unsigned char *)sd->encrypted_path; 342 cstr.len = le16_to_cpu(sd->len); 343 344 if (cstr.len == 0) 345 return ERR_PTR(-EUCLEAN); 346 347 if (cstr.len + sizeof(*sd) - 1 > max_size) 348 return ERR_PTR(-EUCLEAN); 349 350 err = fscrypt_fname_alloc_buffer(cstr.len, &pstr); 351 if (err) 352 return ERR_PTR(err); 353 354 err = fscrypt_fname_disk_to_usr(inode, 0, 0, &cstr, &pstr); 355 if (err) 356 goto err_kfree; 357 358 err = -EUCLEAN; 359 if (pstr.name[0] == '\0') 360 goto err_kfree; 361 362 pstr.name[pstr.len] = '\0'; 363 364 /* 365 * Cache decrypted symlink targets in i_link for later use. Don't cache 366 * symlink targets encoded without the key, since those become outdated 367 * once the key is added. This pairs with the READ_ONCE() above and in 368 * the VFS path lookup code. 369 */ 370 if (!has_key || 371 cmpxchg_release(&inode->i_link, NULL, pstr.name) != NULL) 372 set_delayed_call(done, kfree_link, pstr.name); 373 374 return pstr.name; 375 376 err_kfree: 377 kfree(pstr.name); 378 return ERR_PTR(err); 379 } 380 EXPORT_SYMBOL_GPL(fscrypt_get_symlink); 381