// SPDX-License-Identifier: GPL-2.0-only /* * fs/crypto/hooks.c * * Encryption hooks for higher-level filesystem operations. */ #include <linux/export.h> #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 *dentry, *dentry_parent; struct inode *inode_parent; err = fscrypt_require_key(inode); if (err) return err; dentry = file_dentry(filp); /* * Getting a reference to the parent dentry is needed for the actual * encryption policy comparison, but it's expensive on multi-core * systems. Since this function runs on unencrypted files too, start * with a lightweight RCU-mode check for the parent directory being * unencrypted (in which case it's fine for the child to be either * unencrypted, or encrypted with any policy). Only continue on to the * full policy check if the parent directory is actually encrypted. */ rcu_read_lock(); dentry_parent = READ_ONCE(dentry->d_parent); inode_parent = d_inode_rcu(dentry_parent); if (inode_parent != NULL && !IS_ENCRYPTED(inode_parent)) { rcu_read_unlock(); return 0; } rcu_read_unlock(); dentry_parent = dget_parent(dentry); if (!fscrypt_has_permitted_context(d_inode(dentry_parent), inode)) { fscrypt_warn(inode, "Inconsistent encryption context (parent directory: %lu)", d_inode(dentry_parent)->i_ino); err = -EPERM; } dput(dentry_parent); return err; } EXPORT_SYMBOL_GPL(fscrypt_file_open); int __fscrypt_prepare_link(struct inode *inode, struct inode *dir, struct dentry *dentry) { if (fscrypt_is_nokey_name(dentry)) return -ENOKEY; /* * We don't need to separately check that the directory inode's key is * available, as it's implied by the dentry not being a no-key name. */ 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) { if (fscrypt_is_nokey_name(old_dentry) || fscrypt_is_nokey_name(new_dentry)) return -ENOKEY; /* * We don't need to separately check that the directory inodes' keys are * available, as it's implied by the dentries not being no-key names. */ 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; fscrypt_prepare_dentry(dentry, fname->is_nokey_name); return err; } EXPORT_SYMBOL_GPL(__fscrypt_prepare_lookup); /** * fscrypt_prepare_lookup_partial() - prepare lookup without filename setup * @dir: the encrypted directory being searched * @dentry: the dentry being looked up in @dir * * This function should be used by the ->lookup and ->atomic_open methods of * filesystems that handle filename encryption and no-key name encoding * themselves and thus can't use fscrypt_prepare_lookup(). Like * fscrypt_prepare_lookup(), this will try to set up the directory's encryption * key and will set DCACHE_NOKEY_NAME on the dentry if the key is unavailable. * However, this function doesn't set up a struct fscrypt_name for the filename. * * Return: 0 on success; -errno on error. Note that the encryption key being * unavailable is not considered an error. It is also not an error if * the encryption policy is unsupported by this kernel; that is treated * like the key being unavailable, so that files can still be deleted. */ int fscrypt_prepare_lookup_partial(struct inode *dir, struct dentry *dentry) { int err = fscrypt_get_encryption_info(dir, true); bool is_nokey_name = (!err && !fscrypt_has_encryption_key(dir)); fscrypt_prepare_dentry(dentry, is_nokey_name); return err; } EXPORT_SYMBOL_GPL(fscrypt_prepare_lookup_partial); int __fscrypt_prepare_readdir(struct inode *dir) { return fscrypt_get_encryption_info(dir, true); } EXPORT_SYMBOL_GPL(__fscrypt_prepare_readdir); int __fscrypt_prepare_setattr(struct dentry *dentry, struct iattr *attr) { if (attr->ia_valid & ATTR_SIZE) return fscrypt_require_key(d_inode(dentry)); return 0; } EXPORT_SYMBOL_GPL(__fscrypt_prepare_setattr); /** * fscrypt_prepare_setflags() - prepare to change flags with FS_IOC_SETFLAGS * @inode: the inode on which flags are being changed * @oldflags: the old flags * @flags: the new flags * * The caller should be holding i_rwsem for write. * * Return: 0 on success; -errno if the flags change isn't allowed or if * another error occurs. */ int fscrypt_prepare_setflags(struct inode *inode, unsigned int oldflags, unsigned int flags) { struct fscrypt_inode_info *ci; struct fscrypt_master_key *mk; int err; /* * When the CASEFOLD flag is set on an encrypted directory, we must * derive the secret key needed for the dirhash. This is only possible * if the directory uses a v2 encryption policy. */ if (IS_ENCRYPTED(inode) && (flags & ~oldflags & FS_CASEFOLD_FL)) { err = fscrypt_require_key(inode); if (err) return err; ci = fscrypt_get_inode_info_raw(inode); if (ci->ci_policy.version != FSCRYPT_POLICY_V2) return -EINVAL; mk = ci->ci_master_key; down_read(&mk->mk_sem); if (mk->mk_present) fscrypt_derive_dirhash_key(ci, mk); else err = -ENOKEY; up_read(&mk->mk_sem); return err; } return 0; } /** * fscrypt_prepare_symlink() - prepare to create a possibly-encrypted symlink * @dir: directory in which the symlink is being created * @target: plaintext symlink target * @len: length of @target excluding null terminator * @max_len: space the filesystem has available to store the symlink target * @disk_link: (out) the on-disk symlink target being prepared * * This function computes the size the symlink target will require on-disk, * stores it in @disk_link->len, and validates it against @max_len. An * encrypted symlink may be longer than the original. * * Additionally, @disk_link->name is set to @target if the symlink will be * unencrypted, but left NULL if the symlink will be encrypted. For encrypted * symlinks, the filesystem must call fscrypt_encrypt_symlink() to create the * on-disk target later. (The reason for the two-step process is that some * filesystems need to know the size of the symlink target before creating the * inode, e.g. to determine whether it will be a "fast" or "slow" symlink.) * * Return: 0 on success, -ENAMETOOLONG if the symlink target is too long, * -ENOKEY if the encryption key is missing, or another -errno code if a problem * occurred while setting up the encryption key. */ int fscrypt_prepare_symlink(struct inode *dir, const char *target, unsigned int len, unsigned int max_len, struct fscrypt_str *disk_link) { const union fscrypt_policy *policy; /* * 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. */ policy = fscrypt_policy_to_inherit(dir); if (policy == NULL) { /* Not encrypted */ disk_link->name = (unsigned char *)target; disk_link->len = len + 1; if (disk_link->len > max_len) return -ENAMETOOLONG; return 0; } if (IS_ERR(policy)) return PTR_ERR(policy); /* * 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(policy, len, max_len - sizeof(struct fscrypt_symlink_data) - 1, &disk_link->len)) return -ENAMETOOLONG; disk_link->len += sizeof(struct fscrypt_symlink_data) + 1; 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; /* * fscrypt_prepare_new_inode() should have already set up the new * symlink inode's encryption key. We don't wait until now to do it, * since we may be in a filesystem transaction now. */ if (WARN_ON_ONCE(!fscrypt_has_encryption_key(inode))) return -ENOKEY; 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) - 1; sd->len = cpu_to_le16(ciphertext_len); err = fscrypt_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_ONCE(!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, false); 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) + 1) 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) > max_size) return ERR_PTR(-EUCLEAN); err = fscrypt_fname_alloc_buffer(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); /** * fscrypt_symlink_getattr() - set the correct st_size for encrypted symlinks * @path: the path for the encrypted symlink being queried * @stat: the struct being filled with the symlink's attributes * * Override st_size of encrypted symlinks to be the length of the decrypted * symlink target (or the no-key encoded symlink target, if the key is * unavailable) rather than the length of the encrypted symlink target. This is * necessary for st_size to match the symlink target that userspace actually * sees. POSIX requires this, and some userspace programs depend on it. * * This requires reading the symlink target from disk if needed, setting up the * inode's encryption key if possible, and then decrypting or encoding the * symlink target. This makes lstat() more heavyweight than is normally the * case. However, decrypted symlink targets will be cached in ->i_link, so * usually the symlink won't have to be read and decrypted again later if/when * it is actually followed, readlink() is called, or lstat() is called again. * * Return: 0 on success, -errno on failure */ int fscrypt_symlink_getattr(const struct path *path, struct kstat *stat) { struct dentry *dentry = path->dentry; struct inode *inode = d_inode(dentry); const char *link; DEFINE_DELAYED_CALL(done); /* * To get the symlink target that userspace will see (whether it's the * decrypted target or the no-key encoded target), we can just get it in * the same way the VFS does during path resolution and readlink(). */ link = READ_ONCE(inode->i_link); if (!link) { link = inode->i_op->get_link(dentry, inode, &done); if (IS_ERR(link)) return PTR_ERR(link); } stat->size = strlen(link); do_delayed_call(&done); return 0; } EXPORT_SYMBOL_GPL(fscrypt_symlink_getattr);
