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 ciphertext name before key was added */ 64 if (dentry->d_flags & DCACHE_ENCRYPTED_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 ciphertext name(s) before key was added */ 89 if ((old_dentry->d_flags | new_dentry->d_flags) & 90 DCACHE_ENCRYPTED_NAME) 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_ciphertext_name) { 118 spin_lock(&dentry->d_lock); 119 dentry->d_flags |= DCACHE_ENCRYPTED_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 int __fscrypt_prepare_symlink(struct inode *dir, unsigned int len, 170 unsigned int max_len, 171 struct fscrypt_str *disk_link) 172 { 173 int err; 174 175 /* 176 * To calculate the size of the encrypted symlink target we need to know 177 * the amount of NUL padding, which is determined by the flags set in 178 * the encryption policy which will be inherited from the directory. 179 * The easiest way to get access to this is to just load the directory's 180 * fscrypt_info, since we'll need it to create the dir_entry anyway. 181 * 182 * Note: in test_dummy_encryption mode, @dir may be unencrypted. 183 */ 184 err = fscrypt_get_encryption_info(dir); 185 if (err) 186 return err; 187 if (!fscrypt_has_encryption_key(dir)) 188 return -ENOKEY; 189 190 /* 191 * Calculate the size of the encrypted symlink and verify it won't 192 * exceed max_len. Note that for historical reasons, encrypted symlink 193 * targets are prefixed with the ciphertext length, despite this 194 * actually being redundant with i_size. This decreases by 2 bytes the 195 * longest symlink target we can accept. 196 * 197 * We could recover 1 byte by not counting a null terminator, but 198 * counting it (even though it is meaningless for ciphertext) is simpler 199 * for now since filesystems will assume it is there and subtract it. 200 */ 201 if (!fscrypt_fname_encrypted_size(dir, len, 202 max_len - sizeof(struct fscrypt_symlink_data), 203 &disk_link->len)) 204 return -ENAMETOOLONG; 205 disk_link->len += sizeof(struct fscrypt_symlink_data); 206 207 disk_link->name = NULL; 208 return 0; 209 } 210 EXPORT_SYMBOL_GPL(__fscrypt_prepare_symlink); 211 212 int __fscrypt_encrypt_symlink(struct inode *inode, const char *target, 213 unsigned int len, struct fscrypt_str *disk_link) 214 { 215 int err; 216 struct qstr iname = QSTR_INIT(target, len); 217 struct fscrypt_symlink_data *sd; 218 unsigned int ciphertext_len; 219 220 err = fscrypt_require_key(inode); 221 if (err) 222 return err; 223 224 if (disk_link->name) { 225 /* filesystem-provided buffer */ 226 sd = (struct fscrypt_symlink_data *)disk_link->name; 227 } else { 228 sd = kmalloc(disk_link->len, GFP_NOFS); 229 if (!sd) 230 return -ENOMEM; 231 } 232 ciphertext_len = disk_link->len - sizeof(*sd); 233 sd->len = cpu_to_le16(ciphertext_len); 234 235 err = fscrypt_fname_encrypt(inode, &iname, sd->encrypted_path, 236 ciphertext_len); 237 if (err) 238 goto err_free_sd; 239 240 /* 241 * Null-terminating the ciphertext doesn't make sense, but we still 242 * count the null terminator in the length, so we might as well 243 * initialize it just in case the filesystem writes it out. 244 */ 245 sd->encrypted_path[ciphertext_len] = '\0'; 246 247 /* Cache the plaintext symlink target for later use by get_link() */ 248 err = -ENOMEM; 249 inode->i_link = kmemdup(target, len + 1, GFP_NOFS); 250 if (!inode->i_link) 251 goto err_free_sd; 252 253 if (!disk_link->name) 254 disk_link->name = (unsigned char *)sd; 255 return 0; 256 257 err_free_sd: 258 if (!disk_link->name) 259 kfree(sd); 260 return err; 261 } 262 EXPORT_SYMBOL_GPL(__fscrypt_encrypt_symlink); 263 264 /** 265 * fscrypt_get_symlink() - get the target of an encrypted symlink 266 * @inode: the symlink inode 267 * @caddr: the on-disk contents of the symlink 268 * @max_size: size of @caddr buffer 269 * @done: if successful, will be set up to free the returned target if needed 270 * 271 * If the symlink's encryption key is available, we decrypt its target. 272 * Otherwise, we encode its target for presentation. 273 * 274 * This may sleep, so the filesystem must have dropped out of RCU mode already. 275 * 276 * Return: the presentable symlink target or an ERR_PTR() 277 */ 278 const char *fscrypt_get_symlink(struct inode *inode, const void *caddr, 279 unsigned int max_size, 280 struct delayed_call *done) 281 { 282 const struct fscrypt_symlink_data *sd; 283 struct fscrypt_str cstr, pstr; 284 bool has_key; 285 int err; 286 287 /* This is for encrypted symlinks only */ 288 if (WARN_ON(!IS_ENCRYPTED(inode))) 289 return ERR_PTR(-EINVAL); 290 291 /* If the decrypted target is already cached, just return it. */ 292 pstr.name = READ_ONCE(inode->i_link); 293 if (pstr.name) 294 return pstr.name; 295 296 /* 297 * Try to set up the symlink's encryption key, but we can continue 298 * regardless of whether the key is available or not. 299 */ 300 err = fscrypt_get_encryption_info(inode); 301 if (err) 302 return ERR_PTR(err); 303 has_key = fscrypt_has_encryption_key(inode); 304 305 /* 306 * For historical reasons, encrypted symlink targets are prefixed with 307 * the ciphertext length, even though this is redundant with i_size. 308 */ 309 310 if (max_size < sizeof(*sd)) 311 return ERR_PTR(-EUCLEAN); 312 sd = caddr; 313 cstr.name = (unsigned char *)sd->encrypted_path; 314 cstr.len = le16_to_cpu(sd->len); 315 316 if (cstr.len == 0) 317 return ERR_PTR(-EUCLEAN); 318 319 if (cstr.len + sizeof(*sd) - 1 > max_size) 320 return ERR_PTR(-EUCLEAN); 321 322 err = fscrypt_fname_alloc_buffer(inode, cstr.len, &pstr); 323 if (err) 324 return ERR_PTR(err); 325 326 err = fscrypt_fname_disk_to_usr(inode, 0, 0, &cstr, &pstr); 327 if (err) 328 goto err_kfree; 329 330 err = -EUCLEAN; 331 if (pstr.name[0] == '\0') 332 goto err_kfree; 333 334 pstr.name[pstr.len] = '\0'; 335 336 /* 337 * Cache decrypted symlink targets in i_link for later use. Don't cache 338 * symlink targets encoded without the key, since those become outdated 339 * once the key is added. This pairs with the READ_ONCE() above and in 340 * the VFS path lookup code. 341 */ 342 if (!has_key || 343 cmpxchg_release(&inode->i_link, NULL, pstr.name) != NULL) 344 set_delayed_call(done, kfree_link, pstr.name); 345 346 return pstr.name; 347 348 err_kfree: 349 kfree(pstr.name); 350 return ERR_PTR(err); 351 } 352 EXPORT_SYMBOL_GPL(fscrypt_get_symlink); 353