diff options
Diffstat (limited to 'fs/crypto/hooks.c')
| -rw-r--r-- | fs/crypto/hooks.c | 456 |
1 files changed, 456 insertions, 0 deletions
diff --git a/fs/crypto/hooks.c b/fs/crypto/hooks.c new file mode 100644 index 0000000000..6238dbcadc --- /dev/null +++ b/fs/crypto/hooks.c @@ -0,0 +1,456 @@ +// SPDX-License-Identifier: GPL-2.0-only +/* + * 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) +{ + 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; + + if (fname->is_nokey_name) { + spin_lock(&dentry->d_lock); + dentry->d_flags |= DCACHE_NOKEY_NAME; + spin_unlock(&dentry->d_lock); + } + 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); + + if (!err && !fscrypt_has_encryption_key(dir)) { + spin_lock(&dentry->d_lock); + dentry->d_flags |= DCACHE_NOKEY_NAME; + spin_unlock(&dentry->d_lock); + } + 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_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 = inode->i_crypt_info; + if (ci->ci_policy.version != FSCRYPT_POLICY_V2) + return -EINVAL; + mk = ci->ci_master_key; + down_read(&mk->mk_sem); + if (is_master_key_secret_present(&mk->mk_secret)) + err = 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); |