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 pr_warn_ratelimited("fscrypt: inconsistent encryption contexts: %lu/%lu", 43 d_inode(dir)->i_ino, inode->i_ino); 44 err = -EPERM; 45 } 46 dput(dir); 47 return err; 48 } 49 EXPORT_SYMBOL_GPL(fscrypt_file_open); 50 51 int __fscrypt_prepare_link(struct inode *inode, struct inode *dir) 52 { 53 int err; 54 55 err = fscrypt_require_key(dir); 56 if (err) 57 return err; 58 59 if (!fscrypt_has_permitted_context(dir, inode)) 60 return -EPERM; 61 62 return 0; 63 } 64 EXPORT_SYMBOL_GPL(__fscrypt_prepare_link); 65 66 int __fscrypt_prepare_rename(struct inode *old_dir, struct dentry *old_dentry, 67 struct inode *new_dir, struct dentry *new_dentry, 68 unsigned int flags) 69 { 70 int err; 71 72 err = fscrypt_require_key(old_dir); 73 if (err) 74 return err; 75 76 err = fscrypt_require_key(new_dir); 77 if (err) 78 return err; 79 80 if (old_dir != new_dir) { 81 if (IS_ENCRYPTED(new_dir) && 82 !fscrypt_has_permitted_context(new_dir, 83 d_inode(old_dentry))) 84 return -EPERM; 85 86 if ((flags & RENAME_EXCHANGE) && 87 IS_ENCRYPTED(old_dir) && 88 !fscrypt_has_permitted_context(old_dir, 89 d_inode(new_dentry))) 90 return -EPERM; 91 } 92 return 0; 93 } 94 EXPORT_SYMBOL_GPL(__fscrypt_prepare_rename); 95 96 int __fscrypt_prepare_lookup(struct inode *dir, struct dentry *dentry) 97 { 98 int err = fscrypt_get_encryption_info(dir); 99 100 if (err) 101 return err; 102 103 if (fscrypt_has_encryption_key(dir)) { 104 spin_lock(&dentry->d_lock); 105 dentry->d_flags |= DCACHE_ENCRYPTED_WITH_KEY; 106 spin_unlock(&dentry->d_lock); 107 } 108 109 d_set_d_op(dentry, &fscrypt_d_ops); 110 return 0; 111 } 112 EXPORT_SYMBOL_GPL(__fscrypt_prepare_lookup); 113 114 int __fscrypt_prepare_symlink(struct inode *dir, unsigned int len, 115 unsigned int max_len, 116 struct fscrypt_str *disk_link) 117 { 118 int err; 119 120 /* 121 * To calculate the size of the encrypted symlink target we need to know 122 * the amount of NUL padding, which is determined by the flags set in 123 * the encryption policy which will be inherited from the directory. 124 * The easiest way to get access to this is to just load the directory's 125 * fscrypt_info, since we'll need it to create the dir_entry anyway. 126 * 127 * Note: in test_dummy_encryption mode, @dir may be unencrypted. 128 */ 129 err = fscrypt_get_encryption_info(dir); 130 if (err) 131 return err; 132 if (!fscrypt_has_encryption_key(dir)) 133 return -ENOKEY; 134 135 /* 136 * Calculate the size of the encrypted symlink and verify it won't 137 * exceed max_len. Note that for historical reasons, encrypted symlink 138 * targets are prefixed with the ciphertext length, despite this 139 * actually being redundant with i_size. This decreases by 2 bytes the 140 * longest symlink target we can accept. 141 * 142 * We could recover 1 byte by not counting a null terminator, but 143 * counting it (even though it is meaningless for ciphertext) is simpler 144 * for now since filesystems will assume it is there and subtract it. 145 */ 146 if (!fscrypt_fname_encrypted_size(dir, len, 147 max_len - sizeof(struct fscrypt_symlink_data), 148 &disk_link->len)) 149 return -ENAMETOOLONG; 150 disk_link->len += sizeof(struct fscrypt_symlink_data); 151 152 disk_link->name = NULL; 153 return 0; 154 } 155 EXPORT_SYMBOL_GPL(__fscrypt_prepare_symlink); 156 157 int __fscrypt_encrypt_symlink(struct inode *inode, const char *target, 158 unsigned int len, struct fscrypt_str *disk_link) 159 { 160 int err; 161 struct qstr iname = QSTR_INIT(target, len); 162 struct fscrypt_symlink_data *sd; 163 unsigned int ciphertext_len; 164 165 err = fscrypt_require_key(inode); 166 if (err) 167 return err; 168 169 if (disk_link->name) { 170 /* filesystem-provided buffer */ 171 sd = (struct fscrypt_symlink_data *)disk_link->name; 172 } else { 173 sd = kmalloc(disk_link->len, GFP_NOFS); 174 if (!sd) 175 return -ENOMEM; 176 } 177 ciphertext_len = disk_link->len - sizeof(*sd); 178 sd->len = cpu_to_le16(ciphertext_len); 179 180 err = fname_encrypt(inode, &iname, sd->encrypted_path, ciphertext_len); 181 if (err) { 182 if (!disk_link->name) 183 kfree(sd); 184 return err; 185 } 186 /* 187 * Null-terminating the ciphertext doesn't make sense, but we still 188 * count the null terminator in the length, so we might as well 189 * initialize it just in case the filesystem writes it out. 190 */ 191 sd->encrypted_path[ciphertext_len] = '\0'; 192 193 if (!disk_link->name) 194 disk_link->name = (unsigned char *)sd; 195 return 0; 196 } 197 EXPORT_SYMBOL_GPL(__fscrypt_encrypt_symlink); 198 199 /** 200 * fscrypt_get_symlink - get the target of an encrypted symlink 201 * @inode: the symlink inode 202 * @caddr: the on-disk contents of the symlink 203 * @max_size: size of @caddr buffer 204 * @done: if successful, will be set up to free the returned target 205 * 206 * If the symlink's encryption key is available, we decrypt its target. 207 * Otherwise, we encode its target for presentation. 208 * 209 * This may sleep, so the filesystem must have dropped out of RCU mode already. 210 * 211 * Return: the presentable symlink target or an ERR_PTR() 212 */ 213 const char *fscrypt_get_symlink(struct inode *inode, const void *caddr, 214 unsigned int max_size, 215 struct delayed_call *done) 216 { 217 const struct fscrypt_symlink_data *sd; 218 struct fscrypt_str cstr, pstr; 219 int err; 220 221 /* This is for encrypted symlinks only */ 222 if (WARN_ON(!IS_ENCRYPTED(inode))) 223 return ERR_PTR(-EINVAL); 224 225 /* 226 * Try to set up the symlink's encryption key, but we can continue 227 * regardless of whether the key is available or not. 228 */ 229 err = fscrypt_get_encryption_info(inode); 230 if (err) 231 return ERR_PTR(err); 232 233 /* 234 * For historical reasons, encrypted symlink targets are prefixed with 235 * the ciphertext length, even though this is redundant with i_size. 236 */ 237 238 if (max_size < sizeof(*sd)) 239 return ERR_PTR(-EUCLEAN); 240 sd = caddr; 241 cstr.name = (unsigned char *)sd->encrypted_path; 242 cstr.len = le16_to_cpu(sd->len); 243 244 if (cstr.len == 0) 245 return ERR_PTR(-EUCLEAN); 246 247 if (cstr.len + sizeof(*sd) - 1 > max_size) 248 return ERR_PTR(-EUCLEAN); 249 250 err = fscrypt_fname_alloc_buffer(inode, cstr.len, &pstr); 251 if (err) 252 return ERR_PTR(err); 253 254 err = fscrypt_fname_disk_to_usr(inode, 0, 0, &cstr, &pstr); 255 if (err) 256 goto err_kfree; 257 258 err = -EUCLEAN; 259 if (pstr.name[0] == '\0') 260 goto err_kfree; 261 262 pstr.name[pstr.len] = '\0'; 263 set_delayed_call(done, kfree_link, pstr.name); 264 return pstr.name; 265 266 err_kfree: 267 kfree(pstr.name); 268 return ERR_PTR(err); 269 } 270 EXPORT_SYMBOL_GPL(fscrypt_get_symlink); 271