1 /* 2 * fs/crypto/hooks.c 3 * 4 * Encryption hooks for higher-level filesystem operations. 5 */ 6 7 #include <linux/ratelimit.h> 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 { 109 int err = fscrypt_get_encryption_info(dir); 110 111 if (err) 112 return err; 113 114 if (!fscrypt_has_encryption_key(dir)) { 115 spin_lock(&dentry->d_lock); 116 dentry->d_flags |= DCACHE_ENCRYPTED_NAME; 117 spin_unlock(&dentry->d_lock); 118 d_set_d_op(dentry, &fscrypt_d_ops); 119 } 120 return 0; 121 } 122 EXPORT_SYMBOL_GPL(__fscrypt_prepare_lookup); 123 124 int __fscrypt_prepare_symlink(struct inode *dir, unsigned int len, 125 unsigned int max_len, 126 struct fscrypt_str *disk_link) 127 { 128 int err; 129 130 /* 131 * To calculate the size of the encrypted symlink target we need to know 132 * the amount of NUL padding, which is determined by the flags set in 133 * the encryption policy which will be inherited from the directory. 134 * The easiest way to get access to this is to just load the directory's 135 * fscrypt_info, since we'll need it to create the dir_entry anyway. 136 * 137 * Note: in test_dummy_encryption mode, @dir may be unencrypted. 138 */ 139 err = fscrypt_get_encryption_info(dir); 140 if (err) 141 return err; 142 if (!fscrypt_has_encryption_key(dir)) 143 return -ENOKEY; 144 145 /* 146 * Calculate the size of the encrypted symlink and verify it won't 147 * exceed max_len. Note that for historical reasons, encrypted symlink 148 * targets are prefixed with the ciphertext length, despite this 149 * actually being redundant with i_size. This decreases by 2 bytes the 150 * longest symlink target we can accept. 151 * 152 * We could recover 1 byte by not counting a null terminator, but 153 * counting it (even though it is meaningless for ciphertext) is simpler 154 * for now since filesystems will assume it is there and subtract it. 155 */ 156 if (!fscrypt_fname_encrypted_size(dir, len, 157 max_len - sizeof(struct fscrypt_symlink_data), 158 &disk_link->len)) 159 return -ENAMETOOLONG; 160 disk_link->len += sizeof(struct fscrypt_symlink_data); 161 162 disk_link->name = NULL; 163 return 0; 164 } 165 EXPORT_SYMBOL_GPL(__fscrypt_prepare_symlink); 166 167 int __fscrypt_encrypt_symlink(struct inode *inode, const char *target, 168 unsigned int len, struct fscrypt_str *disk_link) 169 { 170 int err; 171 struct qstr iname = QSTR_INIT(target, len); 172 struct fscrypt_symlink_data *sd; 173 unsigned int ciphertext_len; 174 175 err = fscrypt_require_key(inode); 176 if (err) 177 return err; 178 179 if (disk_link->name) { 180 /* filesystem-provided buffer */ 181 sd = (struct fscrypt_symlink_data *)disk_link->name; 182 } else { 183 sd = kmalloc(disk_link->len, GFP_NOFS); 184 if (!sd) 185 return -ENOMEM; 186 } 187 ciphertext_len = disk_link->len - sizeof(*sd); 188 sd->len = cpu_to_le16(ciphertext_len); 189 190 err = fname_encrypt(inode, &iname, sd->encrypted_path, ciphertext_len); 191 if (err) { 192 if (!disk_link->name) 193 kfree(sd); 194 return err; 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 if (!disk_link->name) 204 disk_link->name = (unsigned char *)sd; 205 return 0; 206 } 207 EXPORT_SYMBOL_GPL(__fscrypt_encrypt_symlink); 208 209 /** 210 * fscrypt_get_symlink - get the target of an encrypted symlink 211 * @inode: the symlink inode 212 * @caddr: the on-disk contents of the symlink 213 * @max_size: size of @caddr buffer 214 * @done: if successful, will be set up to free the returned target 215 * 216 * If the symlink's encryption key is available, we decrypt its target. 217 * Otherwise, we encode its target for presentation. 218 * 219 * This may sleep, so the filesystem must have dropped out of RCU mode already. 220 * 221 * Return: the presentable symlink target or an ERR_PTR() 222 */ 223 const char *fscrypt_get_symlink(struct inode *inode, const void *caddr, 224 unsigned int max_size, 225 struct delayed_call *done) 226 { 227 const struct fscrypt_symlink_data *sd; 228 struct fscrypt_str cstr, pstr; 229 int err; 230 231 /* This is for encrypted symlinks only */ 232 if (WARN_ON(!IS_ENCRYPTED(inode))) 233 return ERR_PTR(-EINVAL); 234 235 /* 236 * Try to set up the symlink's encryption key, but we can continue 237 * regardless of whether the key is available or not. 238 */ 239 err = fscrypt_get_encryption_info(inode); 240 if (err) 241 return ERR_PTR(err); 242 243 /* 244 * For historical reasons, encrypted symlink targets are prefixed with 245 * the ciphertext length, even though this is redundant with i_size. 246 */ 247 248 if (max_size < sizeof(*sd)) 249 return ERR_PTR(-EUCLEAN); 250 sd = caddr; 251 cstr.name = (unsigned char *)sd->encrypted_path; 252 cstr.len = le16_to_cpu(sd->len); 253 254 if (cstr.len == 0) 255 return ERR_PTR(-EUCLEAN); 256 257 if (cstr.len + sizeof(*sd) - 1 > max_size) 258 return ERR_PTR(-EUCLEAN); 259 260 err = fscrypt_fname_alloc_buffer(inode, cstr.len, &pstr); 261 if (err) 262 return ERR_PTR(err); 263 264 err = fscrypt_fname_disk_to_usr(inode, 0, 0, &cstr, &pstr); 265 if (err) 266 goto err_kfree; 267 268 err = -EUCLEAN; 269 if (pstr.name[0] == '\0') 270 goto err_kfree; 271 272 pstr.name[pstr.len] = '\0'; 273 set_delayed_call(done, kfree_link, pstr.name); 274 return pstr.name; 275 276 err_kfree: 277 kfree(pstr.name); 278 return ERR_PTR(err); 279 } 280 EXPORT_SYMBOL_GPL(fscrypt_get_symlink); 281