251 lines
9.1 KiB
C
251 lines
9.1 KiB
C
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/*
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* fscrypt.h: declarations for per-file encryption
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*
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* Filesystems that implement per-file encryption include this header
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* file with the __FS_HAS_ENCRYPTION set according to whether that filesystem
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* is being built with encryption support or not.
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*
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* Copyright (C) 2015, Google, Inc.
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*
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* Written by Michael Halcrow, 2015.
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* Modified by Jaegeuk Kim, 2015.
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*/
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#ifndef _LINUX_FSCRYPT_H
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#define _LINUX_FSCRYPT_H
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#include <linux/fs.h>
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#define FS_CRYPTO_BLOCK_SIZE 16
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struct fscrypt_ctx;
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struct fscrypt_info;
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struct fscrypt_str {
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unsigned char *name;
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u32 len;
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};
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struct fscrypt_name {
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const struct qstr *usr_fname;
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struct fscrypt_str disk_name;
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u32 hash;
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u32 minor_hash;
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struct fscrypt_str crypto_buf;
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};
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#define FSTR_INIT(n, l) { .name = n, .len = l }
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#define FSTR_TO_QSTR(f) QSTR_INIT((f)->name, (f)->len)
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#define fname_name(p) ((p)->disk_name.name)
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#define fname_len(p) ((p)->disk_name.len)
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#if __FS_HAS_ENCRYPTION
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#include <linux/fscrypt_supp.h>
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#else
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#include <linux/fscrypt_notsupp.h>
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#endif
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/**
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* fscrypt_require_key - require an inode's encryption key
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* @inode: the inode we need the key for
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*
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* If the inode is encrypted, set up its encryption key if not already done.
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* Then require that the key be present and return -ENOKEY otherwise.
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*
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* No locks are needed, and the key will live as long as the struct inode --- so
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* it won't go away from under you.
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*
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* Return: 0 on success, -ENOKEY if the key is missing, or another -errno code
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* if a problem occurred while setting up the encryption key.
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*/
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static inline int fscrypt_require_key(struct inode *inode)
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{
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if (IS_ENCRYPTED(inode)) {
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int err = fscrypt_get_encryption_info(inode);
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if (err)
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return err;
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if (!fscrypt_has_encryption_key(inode))
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return -ENOKEY;
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}
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return 0;
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}
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/**
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* fscrypt_prepare_link - prepare to link an inode into a possibly-encrypted directory
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* @old_dentry: an existing dentry for the inode being linked
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* @dir: the target directory
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* @dentry: negative dentry for the target filename
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*
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* A new link can only be added to an encrypted directory if the directory's
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* encryption key is available --- since otherwise we'd have no way to encrypt
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* the filename. Therefore, we first set up the directory's encryption key (if
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* not already done) and return an error if it's unavailable.
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*
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* We also verify that the link will not violate the constraint that all files
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* in an encrypted directory tree use the same encryption policy.
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*
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* Return: 0 on success, -ENOKEY if the directory's encryption key is missing,
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* -EPERM if the link would result in an inconsistent encryption policy, or
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* another -errno code.
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*/
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static inline int fscrypt_prepare_link(struct dentry *old_dentry,
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struct inode *dir,
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struct dentry *dentry)
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{
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if (IS_ENCRYPTED(dir))
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return __fscrypt_prepare_link(d_inode(old_dentry), dir);
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return 0;
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}
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/**
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* fscrypt_prepare_rename - prepare for a rename between possibly-encrypted directories
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* @old_dir: source directory
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* @old_dentry: dentry for source file
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* @new_dir: target directory
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* @new_dentry: dentry for target location (may be negative unless exchanging)
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* @flags: rename flags (we care at least about %RENAME_EXCHANGE)
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*
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* Prepare for ->rename() where the source and/or target directories may be
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* encrypted. A new link can only be added to an encrypted directory if the
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* directory's encryption key is available --- since otherwise we'd have no way
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* to encrypt the filename. A rename to an existing name, on the other hand,
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* *is* cryptographically possible without the key. However, we take the more
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* conservative approach and just forbid all no-key renames.
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*
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* We also verify that the rename will not violate the constraint that all files
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* in an encrypted directory tree use the same encryption policy.
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*
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* Return: 0 on success, -ENOKEY if an encryption key is missing, -EPERM if the
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* rename would cause inconsistent encryption policies, or another -errno code.
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*/
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static inline int fscrypt_prepare_rename(struct inode *old_dir,
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struct dentry *old_dentry,
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struct inode *new_dir,
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struct dentry *new_dentry,
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unsigned int flags)
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{
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if (IS_ENCRYPTED(old_dir) || IS_ENCRYPTED(new_dir))
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return __fscrypt_prepare_rename(old_dir, old_dentry,
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new_dir, new_dentry, flags);
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return 0;
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}
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/**
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* fscrypt_prepare_lookup - prepare to lookup a name in a possibly-encrypted directory
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* @dir: directory being searched
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* @dentry: filename being looked up
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* @flags: lookup flags
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*
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* Prepare for ->lookup() in a directory which may be encrypted. Lookups can be
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* done with or without the directory's encryption key; without the key,
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* filenames are presented in encrypted form. Therefore, we'll try to set up
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* the directory's encryption key, but even without it the lookup can continue.
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*
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* To allow invalidating stale dentries if the directory's encryption key is
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* added later, we also install a custom ->d_revalidate() method and use the
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* DCACHE_ENCRYPTED_WITH_KEY flag to indicate whether a given dentry is a
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* plaintext name (flag set) or a ciphertext name (flag cleared).
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*
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* Return: 0 on success, -errno if a problem occurred while setting up the
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* encryption key
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*/
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static inline int fscrypt_prepare_lookup(struct inode *dir,
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struct dentry *dentry,
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unsigned int flags)
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{
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if (IS_ENCRYPTED(dir))
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return __fscrypt_prepare_lookup(dir, dentry);
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return 0;
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}
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/**
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* fscrypt_prepare_setattr - prepare to change a possibly-encrypted inode's attributes
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* @dentry: dentry through which the inode is being changed
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* @attr: attributes to change
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*
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* Prepare for ->setattr() on a possibly-encrypted inode. On an encrypted file,
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* most attribute changes are allowed even without the encryption key. However,
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* without the encryption key we do have to forbid truncates. This is needed
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* because the size being truncated to may not be a multiple of the filesystem
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* block size, and in that case we'd have to decrypt the final block, zero the
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* portion past i_size, and re-encrypt it. (We *could* allow truncating to a
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* filesystem block boundary, but it's simpler to just forbid all truncates ---
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* and we already forbid all other contents modifications without the key.)
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*
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* Return: 0 on success, -ENOKEY if the key is missing, or another -errno code
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* if a problem occurred while setting up the encryption key.
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*/
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static inline int fscrypt_prepare_setattr(struct dentry *dentry,
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struct iattr *attr)
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{
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if (attr->ia_valid & ATTR_SIZE)
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return fscrypt_require_key(d_inode(dentry));
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return 0;
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}
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/**
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* fscrypt_prepare_symlink - prepare to create a possibly-encrypted symlink
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* @dir: directory in which the symlink is being created
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* @target: plaintext symlink target
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* @len: length of @target excluding null terminator
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* @max_len: space the filesystem has available to store the symlink target
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* @disk_link: (out) the on-disk symlink target being prepared
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*
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* This function computes the size the symlink target will require on-disk,
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* stores it in @disk_link->len, and validates it against @max_len. An
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* encrypted symlink may be longer than the original.
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*
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* Additionally, @disk_link->name is set to @target if the symlink will be
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* unencrypted, but left NULL if the symlink will be encrypted. For encrypted
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* symlinks, the filesystem must call fscrypt_encrypt_symlink() to create the
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* on-disk target later. (The reason for the two-step process is that some
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* filesystems need to know the size of the symlink target before creating the
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* inode, e.g. to determine whether it will be a "fast" or "slow" symlink.)
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*
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* Return: 0 on success, -ENAMETOOLONG if the symlink target is too long,
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* -ENOKEY if the encryption key is missing, or another -errno code if a problem
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* occurred while setting up the encryption key.
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*/
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static inline int fscrypt_prepare_symlink(struct inode *dir,
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const char *target,
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unsigned int len,
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unsigned int max_len,
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struct fscrypt_str *disk_link)
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{
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if (IS_ENCRYPTED(dir) || fscrypt_dummy_context_enabled(dir))
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return __fscrypt_prepare_symlink(dir, len, max_len, disk_link);
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disk_link->name = (unsigned char *)target;
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disk_link->len = len + 1;
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if (disk_link->len > max_len)
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return -ENAMETOOLONG;
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return 0;
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}
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/**
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* fscrypt_encrypt_symlink - encrypt the symlink target if needed
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* @inode: symlink inode
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* @target: plaintext symlink target
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* @len: length of @target excluding null terminator
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* @disk_link: (in/out) the on-disk symlink target being prepared
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*
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* If the symlink target needs to be encrypted, then this function encrypts it
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* into @disk_link->name. fscrypt_prepare_symlink() must have been called
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* previously to compute @disk_link->len. If the filesystem did not allocate a
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* buffer for @disk_link->name after calling fscrypt_prepare_link(), then one
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* will be kmalloc()'ed and the filesystem will be responsible for freeing it.
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*
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* Return: 0 on success, -errno on failure
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*/
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static inline int fscrypt_encrypt_symlink(struct inode *inode,
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const char *target,
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unsigned int len,
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struct fscrypt_str *disk_link)
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{
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if (IS_ENCRYPTED(inode))
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return __fscrypt_encrypt_symlink(inode, target, len, disk_link);
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return 0;
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}
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#endif /* _LINUX_FSCRYPT_H */
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