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