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 { 54 int err; 55 56 err = fscrypt_require_key(dir); 57 if (err) 58 return err; 59 60 if (!fscrypt_has_permitted_context(dir, inode)) 61 return -EXDEV; 62 63 return 0; 64 } 65 EXPORT_SYMBOL_GPL(__fscrypt_prepare_link); 66 67 int __fscrypt_prepare_rename(struct inode *old_dir, struct dentry *old_dentry, 68 struct inode *new_dir, struct dentry *new_dentry, 69 unsigned int flags) 70 { 71 int err; 72 73 err = fscrypt_require_key(old_dir); 74 if (err) 75 return err; 76 77 err = fscrypt_require_key(new_dir); 78 if (err) 79 return err; 80 81 if (old_dir != new_dir) { 82 if (IS_ENCRYPTED(new_dir) && 83 !fscrypt_has_permitted_context(new_dir, 84 d_inode(old_dentry))) 85 return -EXDEV; 86 87 if ((flags & RENAME_EXCHANGE) && 88 IS_ENCRYPTED(old_dir) && 89 !fscrypt_has_permitted_context(old_dir, 90 d_inode(new_dentry))) 91 return -EXDEV; 92 } 93 return 0; 94 } 95 EXPORT_SYMBOL_GPL(__fscrypt_prepare_rename); 96 97 int __fscrypt_prepare_lookup(struct inode *dir, struct dentry *dentry) 98 { 99 int err = fscrypt_get_encryption_info(dir); 100 101 if (err) 102 return err; 103 104 if (fscrypt_has_encryption_key(dir)) { 105 spin_lock(&dentry->d_lock); 106 dentry->d_flags |= DCACHE_ENCRYPTED_WITH_KEY; 107 spin_unlock(&dentry->d_lock); 108 } 109 110 d_set_d_op(dentry, &fscrypt_d_ops); 111 return 0; 112 } 113 EXPORT_SYMBOL_GPL(__fscrypt_prepare_lookup); 114 115 int __fscrypt_prepare_symlink(struct inode *dir, unsigned int len, 116 unsigned int max_len, 117 struct fscrypt_str *disk_link) 118 { 119 int err; 120 121 /* 122 * To calculate the size of the encrypted symlink target we need to know 123 * the amount of NUL padding, which is determined by the flags set in 124 * the encryption policy which will be inherited from the directory. 125 * The easiest way to get access to this is to just load the directory's 126 * fscrypt_info, since we'll need it to create the dir_entry anyway. 127 * 128 * Note: in test_dummy_encryption mode, @dir may be unencrypted. 129 */ 130 err = fscrypt_get_encryption_info(dir); 131 if (err) 132 return err; 133 if (!fscrypt_has_encryption_key(dir)) 134 return -ENOKEY; 135 136 /* 137 * Calculate the size of the encrypted symlink and verify it won't 138 * exceed max_len. Note that for historical reasons, encrypted symlink 139 * targets are prefixed with the ciphertext length, despite this 140 * actually being redundant with i_size. This decreases by 2 bytes the 141 * longest symlink target we can accept. 142 * 143 * We could recover 1 byte by not counting a null terminator, but 144 * counting it (even though it is meaningless for ciphertext) is simpler 145 * for now since filesystems will assume it is there and subtract it. 146 */ 147 if (!fscrypt_fname_encrypted_size(dir, len, 148 max_len - sizeof(struct fscrypt_symlink_data), 149 &disk_link->len)) 150 return -ENAMETOOLONG; 151 disk_link->len += sizeof(struct fscrypt_symlink_data); 152 153 disk_link->name = NULL; 154 return 0; 155 } 156 EXPORT_SYMBOL_GPL(__fscrypt_prepare_symlink); 157 158 int __fscrypt_encrypt_symlink(struct inode *inode, const char *target, 159 unsigned int len, struct fscrypt_str *disk_link) 160 { 161 int err; 162 struct qstr iname = QSTR_INIT(target, len); 163 struct fscrypt_symlink_data *sd; 164 unsigned int ciphertext_len; 165 166 err = fscrypt_require_key(inode); 167 if (err) 168 return err; 169 170 if (disk_link->name) { 171 /* filesystem-provided buffer */ 172 sd = (struct fscrypt_symlink_data *)disk_link->name; 173 } else { 174 sd = kmalloc(disk_link->len, GFP_NOFS); 175 if (!sd) 176 return -ENOMEM; 177 } 178 ciphertext_len = disk_link->len - sizeof(*sd); 179 sd->len = cpu_to_le16(ciphertext_len); 180 181 err = fname_encrypt(inode, &iname, sd->encrypted_path, ciphertext_len); 182 if (err) { 183 if (!disk_link->name) 184 kfree(sd); 185 return err; 186 } 187 /* 188 * Null-terminating the ciphertext doesn't make sense, but we still 189 * count the null terminator in the length, so we might as well 190 * initialize it just in case the filesystem writes it out. 191 */ 192 sd->encrypted_path[ciphertext_len] = '\0'; 193 194 if (!disk_link->name) 195 disk_link->name = (unsigned char *)sd; 196 return 0; 197 } 198 EXPORT_SYMBOL_GPL(__fscrypt_encrypt_symlink); 199 200 /** 201 * fscrypt_get_symlink - get the target of an encrypted symlink 202 * @inode: the symlink inode 203 * @caddr: the on-disk contents of the symlink 204 * @max_size: size of @caddr buffer 205 * @done: if successful, will be set up to free the returned target 206 * 207 * If the symlink's encryption key is available, we decrypt its target. 208 * Otherwise, we encode its target for presentation. 209 * 210 * This may sleep, so the filesystem must have dropped out of RCU mode already. 211 * 212 * Return: the presentable symlink target or an ERR_PTR() 213 */ 214 const char *fscrypt_get_symlink(struct inode *inode, const void *caddr, 215 unsigned int max_size, 216 struct delayed_call *done) 217 { 218 const struct fscrypt_symlink_data *sd; 219 struct fscrypt_str cstr, pstr; 220 int err; 221 222 /* This is for encrypted symlinks only */ 223 if (WARN_ON(!IS_ENCRYPTED(inode))) 224 return ERR_PTR(-EINVAL); 225 226 /* 227 * Try to set up the symlink's encryption key, but we can continue 228 * regardless of whether the key is available or not. 229 */ 230 err = fscrypt_get_encryption_info(inode); 231 if (err) 232 return ERR_PTR(err); 233 234 /* 235 * For historical reasons, encrypted symlink targets are prefixed with 236 * the ciphertext length, even though this is redundant with i_size. 237 */ 238 239 if (max_size < sizeof(*sd)) 240 return ERR_PTR(-EUCLEAN); 241 sd = caddr; 242 cstr.name = (unsigned char *)sd->encrypted_path; 243 cstr.len = le16_to_cpu(sd->len); 244 245 if (cstr.len == 0) 246 return ERR_PTR(-EUCLEAN); 247 248 if (cstr.len + sizeof(*sd) - 1 > max_size) 249 return ERR_PTR(-EUCLEAN); 250 251 err = fscrypt_fname_alloc_buffer(inode, cstr.len, &pstr); 252 if (err) 253 return ERR_PTR(err); 254 255 err = fscrypt_fname_disk_to_usr(inode, 0, 0, &cstr, &pstr); 256 if (err) 257 goto err_kfree; 258 259 err = -EUCLEAN; 260 if (pstr.name[0] == '\0') 261 goto err_kfree; 262 263 pstr.name[pstr.len] = '\0'; 264 set_delayed_call(done, kfree_link, pstr.name); 265 return pstr.name; 266 267 err_kfree: 268 kfree(pstr.name); 269 return ERR_PTR(err); 270 } 271 EXPORT_SYMBOL_GPL(fscrypt_get_symlink); 272