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/ratelimit.h> 9 #include "fscrypt_private.h" 10 11 /** 12 * fscrypt_file_open - prepare to open a possibly-encrypted regular file 13 * @inode: the inode being opened 14 * @filp: the struct file being set up 15 * 16 * Currently, an encrypted regular file can only be opened if its encryption key 17 * is available; access to the raw encrypted contents is not supported. 18 * Therefore, we first set up the inode's encryption key (if not already done) 19 * and return an error if it's unavailable. 20 * 21 * We also verify that if the parent directory (from the path via which the file 22 * is being opened) is encrypted, then the inode being opened uses the same 23 * encryption policy. This is needed as part of the enforcement that all files 24 * in an encrypted directory tree use the same encryption policy, as a 25 * protection against certain types of offline attacks. Note that this check is 26 * needed even when opening an *unencrypted* file, since it's forbidden to have 27 * an unencrypted file in an encrypted directory. 28 * 29 * Return: 0 on success, -ENOKEY if the key is missing, or another -errno code 30 */ 31 int fscrypt_file_open(struct inode *inode, struct file *filp) 32 { 33 int err; 34 struct dentry *dir; 35 36 err = fscrypt_require_key(inode); 37 if (err) 38 return err; 39 40 dir = dget_parent(file_dentry(filp)); 41 if (IS_ENCRYPTED(d_inode(dir)) && 42 !fscrypt_has_permitted_context(d_inode(dir), inode)) { 43 fscrypt_warn(inode->i_sb, 44 "inconsistent encryption contexts: %lu/%lu", 45 d_inode(dir)->i_ino, inode->i_ino); 46 err = -EPERM; 47 } 48 dput(dir); 49 return err; 50 } 51 EXPORT_SYMBOL_GPL(fscrypt_file_open); 52 53 int __fscrypt_prepare_link(struct inode *inode, struct inode *dir, 54 struct dentry *dentry) 55 { 56 int err; 57 58 err = fscrypt_require_key(dir); 59 if (err) 60 return err; 61 62 /* ... in case we looked up ciphertext name before key was added */ 63 if (dentry->d_flags & DCACHE_ENCRYPTED_NAME) 64 return -ENOKEY; 65 66 if (!fscrypt_has_permitted_context(dir, inode)) 67 return -EXDEV; 68 69 return 0; 70 } 71 EXPORT_SYMBOL_GPL(__fscrypt_prepare_link); 72 73 int __fscrypt_prepare_rename(struct inode *old_dir, struct dentry *old_dentry, 74 struct inode *new_dir, struct dentry *new_dentry, 75 unsigned int flags) 76 { 77 int err; 78 79 err = fscrypt_require_key(old_dir); 80 if (err) 81 return err; 82 83 err = fscrypt_require_key(new_dir); 84 if (err) 85 return err; 86 87 /* ... in case we looked up ciphertext name(s) before key was added */ 88 if ((old_dentry->d_flags | new_dentry->d_flags) & 89 DCACHE_ENCRYPTED_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_ciphertext_name) { 117 spin_lock(&dentry->d_lock); 118 dentry->d_flags |= DCACHE_ENCRYPTED_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 int __fscrypt_prepare_symlink(struct inode *dir, unsigned int len, 127 unsigned int max_len, 128 struct fscrypt_str *disk_link) 129 { 130 int err; 131 132 /* 133 * To calculate the size of the encrypted symlink target we need to know 134 * the amount of NUL padding, which is determined by the flags set in 135 * the encryption policy which will be inherited from the directory. 136 * The easiest way to get access to this is to just load the directory's 137 * fscrypt_info, since we'll need it to create the dir_entry anyway. 138 * 139 * Note: in test_dummy_encryption mode, @dir may be unencrypted. 140 */ 141 err = fscrypt_get_encryption_info(dir); 142 if (err) 143 return err; 144 if (!fscrypt_has_encryption_key(dir)) 145 return -ENOKEY; 146 147 /* 148 * Calculate the size of the encrypted symlink and verify it won't 149 * exceed max_len. Note that for historical reasons, encrypted symlink 150 * targets are prefixed with the ciphertext length, despite this 151 * actually being redundant with i_size. This decreases by 2 bytes the 152 * longest symlink target we can accept. 153 * 154 * We could recover 1 byte by not counting a null terminator, but 155 * counting it (even though it is meaningless for ciphertext) is simpler 156 * for now since filesystems will assume it is there and subtract it. 157 */ 158 if (!fscrypt_fname_encrypted_size(dir, len, 159 max_len - sizeof(struct fscrypt_symlink_data), 160 &disk_link->len)) 161 return -ENAMETOOLONG; 162 disk_link->len += sizeof(struct fscrypt_symlink_data); 163 164 disk_link->name = NULL; 165 return 0; 166 } 167 EXPORT_SYMBOL_GPL(__fscrypt_prepare_symlink); 168 169 int __fscrypt_encrypt_symlink(struct inode *inode, const char *target, 170 unsigned int len, struct fscrypt_str *disk_link) 171 { 172 int err; 173 struct qstr iname = QSTR_INIT(target, len); 174 struct fscrypt_symlink_data *sd; 175 unsigned int ciphertext_len; 176 177 err = fscrypt_require_key(inode); 178 if (err) 179 return err; 180 181 if (disk_link->name) { 182 /* filesystem-provided buffer */ 183 sd = (struct fscrypt_symlink_data *)disk_link->name; 184 } else { 185 sd = kmalloc(disk_link->len, GFP_NOFS); 186 if (!sd) 187 return -ENOMEM; 188 } 189 ciphertext_len = disk_link->len - sizeof(*sd); 190 sd->len = cpu_to_le16(ciphertext_len); 191 192 err = fname_encrypt(inode, &iname, sd->encrypted_path, ciphertext_len); 193 if (err) 194 goto err_free_sd; 195 196 /* 197 * Null-terminating the ciphertext doesn't make sense, but we still 198 * count the null terminator in the length, so we might as well 199 * initialize it just in case the filesystem writes it out. 200 */ 201 sd->encrypted_path[ciphertext_len] = '\0'; 202 203 /* Cache the plaintext symlink target for later use by get_link() */ 204 err = -ENOMEM; 205 inode->i_link = kmemdup(target, len + 1, GFP_NOFS); 206 if (!inode->i_link) 207 goto err_free_sd; 208 209 if (!disk_link->name) 210 disk_link->name = (unsigned char *)sd; 211 return 0; 212 213 err_free_sd: 214 if (!disk_link->name) 215 kfree(sd); 216 return err; 217 } 218 EXPORT_SYMBOL_GPL(__fscrypt_encrypt_symlink); 219 220 /** 221 * fscrypt_get_symlink - get the target of an encrypted symlink 222 * @inode: the symlink inode 223 * @caddr: the on-disk contents of the symlink 224 * @max_size: size of @caddr buffer 225 * @done: if successful, will be set up to free the returned target if needed 226 * 227 * If the symlink's encryption key is available, we decrypt its target. 228 * Otherwise, we encode its target for presentation. 229 * 230 * This may sleep, so the filesystem must have dropped out of RCU mode already. 231 * 232 * Return: the presentable symlink target or an ERR_PTR() 233 */ 234 const char *fscrypt_get_symlink(struct inode *inode, const void *caddr, 235 unsigned int max_size, 236 struct delayed_call *done) 237 { 238 const struct fscrypt_symlink_data *sd; 239 struct fscrypt_str cstr, pstr; 240 bool has_key; 241 int err; 242 243 /* This is for encrypted symlinks only */ 244 if (WARN_ON(!IS_ENCRYPTED(inode))) 245 return ERR_PTR(-EINVAL); 246 247 /* If the decrypted target is already cached, just return it. */ 248 pstr.name = READ_ONCE(inode->i_link); 249 if (pstr.name) 250 return pstr.name; 251 252 /* 253 * Try to set up the symlink's encryption key, but we can continue 254 * regardless of whether the key is available or not. 255 */ 256 err = fscrypt_get_encryption_info(inode); 257 if (err) 258 return ERR_PTR(err); 259 has_key = fscrypt_has_encryption_key(inode); 260 261 /* 262 * For historical reasons, encrypted symlink targets are prefixed with 263 * the ciphertext length, even though this is redundant with i_size. 264 */ 265 266 if (max_size < sizeof(*sd)) 267 return ERR_PTR(-EUCLEAN); 268 sd = caddr; 269 cstr.name = (unsigned char *)sd->encrypted_path; 270 cstr.len = le16_to_cpu(sd->len); 271 272 if (cstr.len == 0) 273 return ERR_PTR(-EUCLEAN); 274 275 if (cstr.len + sizeof(*sd) - 1 > max_size) 276 return ERR_PTR(-EUCLEAN); 277 278 err = fscrypt_fname_alloc_buffer(inode, cstr.len, &pstr); 279 if (err) 280 return ERR_PTR(err); 281 282 err = fscrypt_fname_disk_to_usr(inode, 0, 0, &cstr, &pstr); 283 if (err) 284 goto err_kfree; 285 286 err = -EUCLEAN; 287 if (pstr.name[0] == '\0') 288 goto err_kfree; 289 290 pstr.name[pstr.len] = '\0'; 291 292 /* 293 * Cache decrypted symlink targets in i_link for later use. Don't cache 294 * symlink targets encoded without the key, since those become outdated 295 * once the key is added. This pairs with the READ_ONCE() above and in 296 * the VFS path lookup code. 297 */ 298 if (!has_key || 299 cmpxchg_release(&inode->i_link, NULL, pstr.name) != NULL) 300 set_delayed_call(done, kfree_link, pstr.name); 301 302 return pstr.name; 303 304 err_kfree: 305 kfree(pstr.name); 306 return ERR_PTR(err); 307 } 308 EXPORT_SYMBOL_GPL(fscrypt_get_symlink); 309