diff options
Diffstat (limited to 'fs/crypto/hooks.c')
-rw-r--r-- | fs/crypto/hooks.c | 306 |
1 files changed, 306 insertions, 0 deletions
diff --git a/fs/crypto/hooks.c b/fs/crypto/hooks.c new file mode 100644 index 000000000000..30b1ca661249 --- /dev/null +++ b/fs/crypto/hooks.c @@ -0,0 +1,306 @@ +/* + * fs/crypto/hooks.c + * + * Encryption hooks for higher-level filesystem operations. + */ + +#include "fscrypt_private.h" + +/** + * fscrypt_file_open - prepare to open a possibly-encrypted regular file + * @inode: the inode being opened + * @filp: the struct file being set up + * + * Currently, an encrypted regular file can only be opened if its encryption key + * is available; access to the raw encrypted contents is not supported. + * Therefore, we first set up the inode's encryption key (if not already done) + * and return an error if it's unavailable. + * + * We also verify that if the parent directory (from the path via which the file + * is being opened) is encrypted, then the inode being opened uses the same + * encryption policy. This is needed as part of the enforcement that all files + * in an encrypted directory tree use the same encryption policy, as a + * protection against certain types of offline attacks. Note that this check is + * needed even when opening an *unencrypted* file, since it's forbidden to have + * an unencrypted file in an encrypted directory. + * + * Return: 0 on success, -ENOKEY if the key is missing, or another -errno code + */ +int fscrypt_file_open(struct inode *inode, struct file *filp) +{ + int err; + struct dentry *dir; + + err = fscrypt_require_key(inode); + if (err) + return err; + + dir = dget_parent(file_dentry(filp)); + if (IS_ENCRYPTED(d_inode(dir)) && + !fscrypt_has_permitted_context(d_inode(dir), inode)) { + fscrypt_warn(inode, + "Inconsistent encryption context (parent directory: %lu)", + d_inode(dir)->i_ino); + err = -EPERM; + } + dput(dir); + return err; +} +EXPORT_SYMBOL_GPL(fscrypt_file_open); + +int __fscrypt_prepare_link(struct inode *inode, struct inode *dir, + struct dentry *dentry) +{ + int err; + + err = fscrypt_require_key(dir); + if (err) + return err; + + /* ... in case we looked up ciphertext name before key was added */ + if (dentry->d_flags & DCACHE_ENCRYPTED_NAME) + return -ENOKEY; + + if (!fscrypt_has_permitted_context(dir, inode)) + return -EXDEV; + + return 0; +} +EXPORT_SYMBOL_GPL(__fscrypt_prepare_link); + +int __fscrypt_prepare_rename(struct inode *old_dir, struct dentry *old_dentry, + struct inode *new_dir, struct dentry *new_dentry, + unsigned int flags) +{ + int err; + + err = fscrypt_require_key(old_dir); + if (err) + return err; + + err = fscrypt_require_key(new_dir); + if (err) + return err; + + /* ... in case we looked up ciphertext name(s) before key was added */ + if ((old_dentry->d_flags | new_dentry->d_flags) & + DCACHE_ENCRYPTED_NAME) + return -ENOKEY; + + if (old_dir != new_dir) { + if (IS_ENCRYPTED(new_dir) && + !fscrypt_has_permitted_context(new_dir, + d_inode(old_dentry))) + return -EXDEV; + + if ((flags & RENAME_EXCHANGE) && + IS_ENCRYPTED(old_dir) && + !fscrypt_has_permitted_context(old_dir, + d_inode(new_dentry))) + return -EXDEV; + } + return 0; +} +EXPORT_SYMBOL_GPL(__fscrypt_prepare_rename); + +int __fscrypt_prepare_lookup(struct inode *dir, struct dentry *dentry, + struct fscrypt_name *fname) +{ + int err = fscrypt_setup_filename(dir, &dentry->d_name, 1, fname); + + if (err && err != -ENOENT) + return err; + + if (fname->is_ciphertext_name) { + spin_lock(&dentry->d_lock); + dentry->d_flags |= DCACHE_ENCRYPTED_NAME; + spin_unlock(&dentry->d_lock); + d_set_d_op(dentry, &fscrypt_d_ops); + } + return err; +} +EXPORT_SYMBOL_GPL(__fscrypt_prepare_lookup); + +int __fscrypt_prepare_symlink(struct inode *dir, unsigned int len, + unsigned int max_len, + struct fscrypt_str *disk_link) +{ + int err; + + /* + * To calculate the size of the encrypted symlink target we need to know + * the amount of NUL padding, which is determined by the flags set in + * the encryption policy which will be inherited from the directory. + * The easiest way to get access to this is to just load the directory's + * fscrypt_info, since we'll need it to create the dir_entry anyway. + * + * Note: in test_dummy_encryption mode, @dir may be unencrypted. + */ + err = fscrypt_get_encryption_info(dir); + if (err) + return err; + if (!fscrypt_has_encryption_key(dir)) + return -ENOKEY; + + /* + * Calculate the size of the encrypted symlink and verify it won't + * exceed max_len. Note that for historical reasons, encrypted symlink + * targets are prefixed with the ciphertext length, despite this + * actually being redundant with i_size. This decreases by 2 bytes the + * longest symlink target we can accept. + * + * We could recover 1 byte by not counting a null terminator, but + * counting it (even though it is meaningless for ciphertext) is simpler + * for now since filesystems will assume it is there and subtract it. + */ + if (!fscrypt_fname_encrypted_size(dir, len, + max_len - sizeof(struct fscrypt_symlink_data), + &disk_link->len)) + return -ENAMETOOLONG; + disk_link->len += sizeof(struct fscrypt_symlink_data); + + disk_link->name = NULL; + return 0; +} +EXPORT_SYMBOL_GPL(__fscrypt_prepare_symlink); + +int __fscrypt_encrypt_symlink(struct inode *inode, const char *target, + unsigned int len, struct fscrypt_str *disk_link) +{ + int err; + struct qstr iname = QSTR_INIT(target, len); + struct fscrypt_symlink_data *sd; + unsigned int ciphertext_len; + + err = fscrypt_require_key(inode); + if (err) + return err; + + if (disk_link->name) { + /* filesystem-provided buffer */ + sd = (struct fscrypt_symlink_data *)disk_link->name; + } else { + sd = kmalloc(disk_link->len, GFP_NOFS); + if (!sd) + return -ENOMEM; + } + ciphertext_len = disk_link->len - sizeof(*sd); + sd->len = cpu_to_le16(ciphertext_len); + + err = fname_encrypt(inode, &iname, sd->encrypted_path, ciphertext_len); + if (err) + goto err_free_sd; + + /* + * Null-terminating the ciphertext doesn't make sense, but we still + * count the null terminator in the length, so we might as well + * initialize it just in case the filesystem writes it out. + */ + sd->encrypted_path[ciphertext_len] = '\0'; + + /* Cache the plaintext symlink target for later use by get_link() */ + err = -ENOMEM; + inode->i_link = kmemdup(target, len + 1, GFP_NOFS); + if (!inode->i_link) + goto err_free_sd; + + if (!disk_link->name) + disk_link->name = (unsigned char *)sd; + return 0; + +err_free_sd: + if (!disk_link->name) + kfree(sd); + return err; +} +EXPORT_SYMBOL_GPL(__fscrypt_encrypt_symlink); + +/** + * fscrypt_get_symlink - get the target of an encrypted symlink + * @inode: the symlink inode + * @caddr: the on-disk contents of the symlink + * @max_size: size of @caddr buffer + * @done: if successful, will be set up to free the returned target if needed + * + * If the symlink's encryption key is available, we decrypt its target. + * Otherwise, we encode its target for presentation. + * + * This may sleep, so the filesystem must have dropped out of RCU mode already. + * + * Return: the presentable symlink target or an ERR_PTR() + */ +const char *fscrypt_get_symlink(struct inode *inode, const void *caddr, + unsigned int max_size, + struct delayed_call *done) +{ + const struct fscrypt_symlink_data *sd; + struct fscrypt_str cstr, pstr; + bool has_key; + int err; + + /* This is for encrypted symlinks only */ + if (WARN_ON(!IS_ENCRYPTED(inode))) + return ERR_PTR(-EINVAL); + + /* If the decrypted target is already cached, just return it. */ + pstr.name = READ_ONCE(inode->i_link); + if (pstr.name) + return pstr.name; + + /* + * Try to set up the symlink's encryption key, but we can continue + * regardless of whether the key is available or not. + */ + err = fscrypt_get_encryption_info(inode); + if (err) + return ERR_PTR(err); + has_key = fscrypt_has_encryption_key(inode); + + /* + * For historical reasons, encrypted symlink targets are prefixed with + * the ciphertext length, even though this is redundant with i_size. + */ + + if (max_size < sizeof(*sd)) + return ERR_PTR(-EUCLEAN); + sd = caddr; + cstr.name = (unsigned char *)sd->encrypted_path; + cstr.len = le16_to_cpu(sd->len); + + if (cstr.len == 0) + return ERR_PTR(-EUCLEAN); + + if (cstr.len + sizeof(*sd) - 1 > max_size) + return ERR_PTR(-EUCLEAN); + + err = fscrypt_fname_alloc_buffer(inode, cstr.len, &pstr); + if (err) + return ERR_PTR(err); + + err = fscrypt_fname_disk_to_usr(inode, 0, 0, &cstr, &pstr); + if (err) + goto err_kfree; + + err = -EUCLEAN; + if (pstr.name[0] == '\0') + goto err_kfree; + + pstr.name[pstr.len] = '\0'; + + /* + * Cache decrypted symlink targets in i_link for later use. Don't cache + * symlink targets encoded without the key, since those become outdated + * once the key is added. This pairs with the READ_ONCE() above and in + * the VFS path lookup code. + */ + if (!has_key || + cmpxchg_release(&inode->i_link, NULL, pstr.name) != NULL) + set_delayed_call(done, kfree_link, pstr.name); + + return pstr.name; + +err_kfree: + kfree(pstr.name); + return ERR_PTR(err); +} +EXPORT_SYMBOL_GPL(fscrypt_get_symlink); |