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 "fscrypt_private.h" 9 10 /** 11 * fscrypt_file_open - prepare to open a possibly-encrypted regular file 12 * @inode: the inode being opened 13 * @filp: the struct file being set up 14 * 15 * Currently, an encrypted regular file can only be opened if its encryption key 16 * is available; access to the raw encrypted contents is not supported. 17 * Therefore, we first set up the inode's encryption key (if not already done) 18 * and return an error if it's unavailable. 19 * 20 * We also verify that if the parent directory (from the path via which the file 21 * is being opened) is encrypted, then the inode being opened uses the same 22 * encryption policy. This is needed as part of the enforcement that all files 23 * in an encrypted directory tree use the same encryption policy, as a 24 * protection against certain types of offline attacks. Note that this check is 25 * needed even when opening an *unencrypted* file, since it's forbidden to have 26 * an unencrypted file in an encrypted directory. 27 * 28 * Return: 0 on success, -ENOKEY if the key is missing, or another -errno code 29 */ 30 int fscrypt_file_open(struct inode *inode, struct file *filp) 31 { 32 int err; 33 struct dentry *dir; 34 35 err = fscrypt_require_key(inode); 36 if (err) 37 return err; 38 39 dir = dget_parent(file_dentry(filp)); 40 if (IS_ENCRYPTED(d_inode(dir)) && 41 !fscrypt_has_permitted_context(d_inode(dir), inode)) { 42 fscrypt_warn(inode->i_sb, 43 "inconsistent encryption contexts: %lu/%lu", 44 d_inode(dir)->i_ino, inode->i_ino); 45 err = -EPERM; 46 } 47 dput(dir); 48 return err; 49 } 50 EXPORT_SYMBOL_GPL(fscrypt_file_open); 51 52 int __fscrypt_prepare_link(struct inode *inode, struct inode *dir, 53 struct dentry *dentry) 54 { 55 int err; 56 57 err = fscrypt_require_key(dir); 58 if (err) 59 return err; 60 61 /* ... in case we looked up ciphertext name before key was added */ 62 if (dentry->d_flags & DCACHE_ENCRYPTED_NAME) 63 return -ENOKEY; 64 65 if (!fscrypt_has_permitted_context(dir, inode)) 66 return -EXDEV; 67 68 return 0; 69 } 70 EXPORT_SYMBOL_GPL(__fscrypt_prepare_link); 71 72 int __fscrypt_prepare_rename(struct inode *old_dir, struct dentry *old_dentry, 73 struct inode *new_dir, struct dentry *new_dentry, 74 unsigned int flags) 75 { 76 int err; 77 78 err = fscrypt_require_key(old_dir); 79 if (err) 80 return err; 81 82 err = fscrypt_require_key(new_dir); 83 if (err) 84 return err; 85 86 /* ... in case we looked up ciphertext name(s) before key was added */ 87 if ((old_dentry->d_flags | new_dentry->d_flags) & 88 DCACHE_ENCRYPTED_NAME) 89 return -ENOKEY; 90 91 if (old_dir != new_dir) { 92 if (IS_ENCRYPTED(new_dir) && 93 !fscrypt_has_permitted_context(new_dir, 94 d_inode(old_dentry))) 95 return -EXDEV; 96 97 if ((flags & RENAME_EXCHANGE) && 98 IS_ENCRYPTED(old_dir) && 99 !fscrypt_has_permitted_context(old_dir, 100 d_inode(new_dentry))) 101 return -EXDEV; 102 } 103 return 0; 104 } 105 EXPORT_SYMBOL_GPL(__fscrypt_prepare_rename); 106 107 int __fscrypt_prepare_lookup(struct inode *dir, struct dentry *dentry, 108 struct fscrypt_name *fname) 109 { 110 int err = fscrypt_setup_filename(dir, &dentry->d_name, 1, fname); 111 112 if (err && err != -ENOENT) 113 return err; 114 115 if (fname->is_ciphertext_name) { 116 spin_lock(&dentry->d_lock); 117 dentry->d_flags |= DCACHE_ENCRYPTED_NAME; 118 spin_unlock(&dentry->d_lock); 119 d_set_d_op(dentry, &fscrypt_d_ops); 120 } 121 return err; 122 } 123 EXPORT_SYMBOL_GPL(__fscrypt_prepare_lookup); 124 125 int __fscrypt_prepare_symlink(struct inode *dir, unsigned int len, 126 unsigned int max_len, 127 struct fscrypt_str *disk_link) 128 { 129 int err; 130 131 /* 132 * To calculate the size of the encrypted symlink target we need to know 133 * the amount of NUL padding, which is determined by the flags set in 134 * the encryption policy which will be inherited from the directory. 135 * The easiest way to get access to this is to just load the directory's 136 * fscrypt_info, since we'll need it to create the dir_entry anyway. 137 * 138 * Note: in test_dummy_encryption mode, @dir may be unencrypted. 139 */ 140 err = fscrypt_get_encryption_info(dir); 141 if (err) 142 return err; 143 if (!fscrypt_has_encryption_key(dir)) 144 return -ENOKEY; 145 146 /* 147 * Calculate the size of the encrypted symlink and verify it won't 148 * exceed max_len. Note that for historical reasons, encrypted symlink 149 * targets are prefixed with the ciphertext length, despite this 150 * actually being redundant with i_size. This decreases by 2 bytes the 151 * longest symlink target we can accept. 152 * 153 * We could recover 1 byte by not counting a null terminator, but 154 * counting it (even though it is meaningless for ciphertext) is simpler 155 * for now since filesystems will assume it is there and subtract it. 156 */ 157 if (!fscrypt_fname_encrypted_size(dir, len, 158 max_len - sizeof(struct fscrypt_symlink_data), 159 &disk_link->len)) 160 return -ENAMETOOLONG; 161 disk_link->len += sizeof(struct fscrypt_symlink_data); 162 163 disk_link->name = NULL; 164 return 0; 165 } 166 EXPORT_SYMBOL_GPL(__fscrypt_prepare_symlink); 167 168 int __fscrypt_encrypt_symlink(struct inode *inode, const char *target, 169 unsigned int len, struct fscrypt_str *disk_link) 170 { 171 int err; 172 struct qstr iname = QSTR_INIT(target, len); 173 struct fscrypt_symlink_data *sd; 174 unsigned int ciphertext_len; 175 176 err = fscrypt_require_key(inode); 177 if (err) 178 return err; 179 180 if (disk_link->name) { 181 /* filesystem-provided buffer */ 182 sd = (struct fscrypt_symlink_data *)disk_link->name; 183 } else { 184 sd = kmalloc(disk_link->len, GFP_NOFS); 185 if (!sd) 186 return -ENOMEM; 187 } 188 ciphertext_len = disk_link->len - sizeof(*sd); 189 sd->len = cpu_to_le16(ciphertext_len); 190 191 err = fname_encrypt(inode, &iname, sd->encrypted_path, ciphertext_len); 192 if (err) 193 goto err_free_sd; 194 195 /* 196 * Null-terminating the ciphertext doesn't make sense, but we still 197 * count the null terminator in the length, so we might as well 198 * initialize it just in case the filesystem writes it out. 199 */ 200 sd->encrypted_path[ciphertext_len] = '\0'; 201 202 /* Cache the plaintext symlink target for later use by get_link() */ 203 err = -ENOMEM; 204 inode->i_link = kmemdup(target, len + 1, GFP_NOFS); 205 if (!inode->i_link) 206 goto err_free_sd; 207 208 if (!disk_link->name) 209 disk_link->name = (unsigned char *)sd; 210 return 0; 211 212 err_free_sd: 213 if (!disk_link->name) 214 kfree(sd); 215 return err; 216 } 217 EXPORT_SYMBOL_GPL(__fscrypt_encrypt_symlink); 218 219 /** 220 * fscrypt_get_symlink - get the target of an encrypted symlink 221 * @inode: the symlink inode 222 * @caddr: the on-disk contents of the symlink 223 * @max_size: size of @caddr buffer 224 * @done: if successful, will be set up to free the returned target if needed 225 * 226 * If the symlink's encryption key is available, we decrypt its target. 227 * Otherwise, we encode its target for presentation. 228 * 229 * This may sleep, so the filesystem must have dropped out of RCU mode already. 230 * 231 * Return: the presentable symlink target or an ERR_PTR() 232 */ 233 const char *fscrypt_get_symlink(struct inode *inode, const void *caddr, 234 unsigned int max_size, 235 struct delayed_call *done) 236 { 237 const struct fscrypt_symlink_data *sd; 238 struct fscrypt_str cstr, pstr; 239 bool has_key; 240 int err; 241 242 /* This is for encrypted symlinks only */ 243 if (WARN_ON(!IS_ENCRYPTED(inode))) 244 return ERR_PTR(-EINVAL); 245 246 /* If the decrypted target is already cached, just return it. */ 247 pstr.name = READ_ONCE(inode->i_link); 248 if (pstr.name) 249 return pstr.name; 250 251 /* 252 * Try to set up the symlink's encryption key, but we can continue 253 * regardless of whether the key is available or not. 254 */ 255 err = fscrypt_get_encryption_info(inode); 256 if (err) 257 return ERR_PTR(err); 258 has_key = fscrypt_has_encryption_key(inode); 259 260 /* 261 * For historical reasons, encrypted symlink targets are prefixed with 262 * the ciphertext length, even though this is redundant with i_size. 263 */ 264 265 if (max_size < sizeof(*sd)) 266 return ERR_PTR(-EUCLEAN); 267 sd = caddr; 268 cstr.name = (unsigned char *)sd->encrypted_path; 269 cstr.len = le16_to_cpu(sd->len); 270 271 if (cstr.len == 0) 272 return ERR_PTR(-EUCLEAN); 273 274 if (cstr.len + sizeof(*sd) - 1 > max_size) 275 return ERR_PTR(-EUCLEAN); 276 277 err = fscrypt_fname_alloc_buffer(inode, cstr.len, &pstr); 278 if (err) 279 return ERR_PTR(err); 280 281 err = fscrypt_fname_disk_to_usr(inode, 0, 0, &cstr, &pstr); 282 if (err) 283 goto err_kfree; 284 285 err = -EUCLEAN; 286 if (pstr.name[0] == '\0') 287 goto err_kfree; 288 289 pstr.name[pstr.len] = '\0'; 290 291 /* 292 * Cache decrypted symlink targets in i_link for later use. Don't cache 293 * symlink targets encoded without the key, since those become outdated 294 * once the key is added. This pairs with the READ_ONCE() above and in 295 * the VFS path lookup code. 296 */ 297 if (!has_key || 298 cmpxchg_release(&inode->i_link, NULL, pstr.name) != NULL) 299 set_delayed_call(done, kfree_link, pstr.name); 300 301 return pstr.name; 302 303 err_kfree: 304 kfree(pstr.name); 305 return ERR_PTR(err); 306 } 307 EXPORT_SYMBOL_GPL(fscrypt_get_symlink); 308