// 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: %llu)",			     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);