424 lines
13 KiB
C
424 lines
13 KiB
C
// SPDX-License-Identifier: GPL-2.0-only
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/*
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* fs/crypto/hooks.c
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*
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* Encryption hooks for higher-level filesystem operations.
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*/
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#include "fscrypt_private.h"
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/**
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* fscrypt_file_open() - prepare to open a possibly-encrypted regular file
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* @inode: the inode being opened
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* @filp: the struct file being set up
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*
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* Currently, an encrypted regular file can only be opened if its encryption key
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* is available; access to the raw encrypted contents is not supported.
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* Therefore, we first set up the inode's encryption key (if not already done)
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* and return an error if it's unavailable.
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*
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* We also verify that if the parent directory (from the path via which the file
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* is being opened) is encrypted, then the inode being opened uses the same
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* encryption policy. This is needed as part of the enforcement that all files
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* in an encrypted directory tree use the same encryption policy, as a
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* protection against certain types of offline attacks. Note that this check is
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* needed even when opening an *unencrypted* file, since it's forbidden to have
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* an unencrypted file in an encrypted directory.
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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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*/
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int fscrypt_file_open(struct inode *inode, struct file *filp)
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{
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int err;
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struct dentry *dir;
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err = fscrypt_require_key(inode);
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if (err)
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return err;
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dir = dget_parent(file_dentry(filp));
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if (IS_ENCRYPTED(d_inode(dir)) &&
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!fscrypt_has_permitted_context(d_inode(dir), inode)) {
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fscrypt_warn(inode,
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"Inconsistent encryption context (parent directory: %lu)",
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d_inode(dir)->i_ino);
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err = -EPERM;
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}
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dput(dir);
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return err;
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}
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EXPORT_SYMBOL_GPL(fscrypt_file_open);
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int __fscrypt_prepare_link(struct inode *inode, struct inode *dir,
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struct dentry *dentry)
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{
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int err;
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err = fscrypt_require_key(dir);
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if (err)
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return err;
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/* ... in case we looked up no-key name before key was added */
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if (fscrypt_is_nokey_name(dentry))
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return -ENOKEY;
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if (!fscrypt_has_permitted_context(dir, inode))
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return -EXDEV;
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return 0;
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}
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EXPORT_SYMBOL_GPL(__fscrypt_prepare_link);
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int __fscrypt_prepare_rename(struct inode *old_dir, struct dentry *old_dentry,
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struct inode *new_dir, struct dentry *new_dentry,
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unsigned int flags)
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{
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int err;
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err = fscrypt_require_key(old_dir);
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if (err)
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return err;
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err = fscrypt_require_key(new_dir);
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if (err)
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return err;
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/* ... in case we looked up no-key name(s) before key was added */
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if (fscrypt_is_nokey_name(old_dentry) ||
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fscrypt_is_nokey_name(new_dentry))
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return -ENOKEY;
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if (old_dir != new_dir) {
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if (IS_ENCRYPTED(new_dir) &&
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!fscrypt_has_permitted_context(new_dir,
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d_inode(old_dentry)))
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return -EXDEV;
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if ((flags & RENAME_EXCHANGE) &&
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IS_ENCRYPTED(old_dir) &&
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!fscrypt_has_permitted_context(old_dir,
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d_inode(new_dentry)))
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return -EXDEV;
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}
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return 0;
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}
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EXPORT_SYMBOL_GPL(__fscrypt_prepare_rename);
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int __fscrypt_prepare_lookup(struct inode *dir, struct dentry *dentry,
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struct fscrypt_name *fname)
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{
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int err = fscrypt_setup_filename(dir, &dentry->d_name, 1, fname);
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if (err && err != -ENOENT)
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return err;
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if (fname->is_nokey_name) {
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spin_lock(&dentry->d_lock);
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dentry->d_flags |= DCACHE_NOKEY_NAME;
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spin_unlock(&dentry->d_lock);
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d_set_d_op(dentry, &fscrypt_d_ops);
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}
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return err;
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}
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EXPORT_SYMBOL_GPL(__fscrypt_prepare_lookup);
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/**
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* fscrypt_prepare_setflags() - prepare to change flags with FS_IOC_SETFLAGS
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* @inode: the inode on which flags are being changed
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* @oldflags: the old flags
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* @flags: the new flags
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*
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* The caller should be holding i_rwsem for write.
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*
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* Return: 0 on success; -errno if the flags change isn't allowed or if
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* another error occurs.
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*/
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int fscrypt_prepare_setflags(struct inode *inode,
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unsigned int oldflags, unsigned int flags)
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{
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struct fscrypt_info *ci;
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struct fscrypt_master_key *mk;
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int err;
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/*
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* When the CASEFOLD flag is set on an encrypted directory, we must
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* derive the secret key needed for the dirhash. This is only possible
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* if the directory uses a v2 encryption policy.
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*/
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if (IS_ENCRYPTED(inode) && (flags & ~oldflags & FS_CASEFOLD_FL)) {
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err = fscrypt_require_key(inode);
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if (err)
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return err;
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ci = inode->i_crypt_info;
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if (ci->ci_policy.version != FSCRYPT_POLICY_V2)
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return -EINVAL;
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mk = ci->ci_master_key;
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down_read(&mk->mk_sem);
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if (is_master_key_secret_present(&mk->mk_secret))
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err = fscrypt_derive_dirhash_key(ci, mk);
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else
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err = -ENOKEY;
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up_read(&mk->mk_sem);
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return err;
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}
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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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int fscrypt_prepare_symlink(struct inode *dir, const char *target,
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unsigned int len, unsigned int max_len,
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struct fscrypt_str *disk_link)
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{
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const union fscrypt_policy *policy;
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/*
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* To calculate the size of the encrypted symlink target we need to know
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* the amount of NUL padding, which is determined by the flags set in
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* the encryption policy which will be inherited from the directory.
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*/
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policy = fscrypt_policy_to_inherit(dir);
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if (policy == NULL) {
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/* Not encrypted */
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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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if (IS_ERR(policy))
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return PTR_ERR(policy);
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/*
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* Calculate the size of the encrypted symlink and verify it won't
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* exceed max_len. Note that for historical reasons, encrypted symlink
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* targets are prefixed with the ciphertext length, despite this
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* actually being redundant with i_size. This decreases by 2 bytes the
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* longest symlink target we can accept.
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*
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* We could recover 1 byte by not counting a null terminator, but
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* counting it (even though it is meaningless for ciphertext) is simpler
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* for now since filesystems will assume it is there and subtract it.
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*/
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if (!fscrypt_fname_encrypted_size(policy, len,
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max_len - sizeof(struct fscrypt_symlink_data),
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&disk_link->len))
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return -ENAMETOOLONG;
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disk_link->len += sizeof(struct fscrypt_symlink_data);
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disk_link->name = NULL;
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return 0;
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}
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EXPORT_SYMBOL_GPL(fscrypt_prepare_symlink);
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int __fscrypt_encrypt_symlink(struct inode *inode, const char *target,
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unsigned int len, struct fscrypt_str *disk_link)
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{
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int err;
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struct qstr iname = QSTR_INIT(target, len);
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struct fscrypt_symlink_data *sd;
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unsigned int ciphertext_len;
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/*
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* fscrypt_prepare_new_inode() should have already set up the new
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* symlink inode's encryption key. We don't wait until now to do it,
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* since we may be in a filesystem transaction now.
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*/
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if (WARN_ON_ONCE(!fscrypt_has_encryption_key(inode)))
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return -ENOKEY;
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if (disk_link->name) {
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/* filesystem-provided buffer */
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sd = (struct fscrypt_symlink_data *)disk_link->name;
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} else {
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sd = kmalloc(disk_link->len, GFP_NOFS);
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if (!sd)
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return -ENOMEM;
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}
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ciphertext_len = disk_link->len - sizeof(*sd);
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sd->len = cpu_to_le16(ciphertext_len);
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err = fscrypt_fname_encrypt(inode, &iname, sd->encrypted_path,
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ciphertext_len);
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if (err)
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goto err_free_sd;
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/*
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* Null-terminating the ciphertext doesn't make sense, but we still
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* count the null terminator in the length, so we might as well
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* initialize it just in case the filesystem writes it out.
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*/
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sd->encrypted_path[ciphertext_len] = '\0';
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/* Cache the plaintext symlink target for later use by get_link() */
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err = -ENOMEM;
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inode->i_link = kmemdup(target, len + 1, GFP_NOFS);
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if (!inode->i_link)
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goto err_free_sd;
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if (!disk_link->name)
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disk_link->name = (unsigned char *)sd;
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return 0;
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err_free_sd:
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if (!disk_link->name)
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kfree(sd);
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return err;
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}
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EXPORT_SYMBOL_GPL(__fscrypt_encrypt_symlink);
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/**
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* fscrypt_get_symlink() - get the target of an encrypted symlink
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* @inode: the symlink inode
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* @caddr: the on-disk contents of the symlink
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* @max_size: size of @caddr buffer
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* @done: if successful, will be set up to free the returned target if needed
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*
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* If the symlink's encryption key is available, we decrypt its target.
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* Otherwise, we encode its target for presentation.
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*
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* This may sleep, so the filesystem must have dropped out of RCU mode already.
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*
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* Return: the presentable symlink target or an ERR_PTR()
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*/
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const char *fscrypt_get_symlink(struct inode *inode, const void *caddr,
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unsigned int max_size,
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struct delayed_call *done)
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{
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const struct fscrypt_symlink_data *sd;
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struct fscrypt_str cstr, pstr;
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bool has_key;
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int err;
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/* This is for encrypted symlinks only */
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if (WARN_ON(!IS_ENCRYPTED(inode)))
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return ERR_PTR(-EINVAL);
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/* If the decrypted target is already cached, just return it. */
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pstr.name = READ_ONCE(inode->i_link);
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if (pstr.name)
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return pstr.name;
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/*
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* Try to set up the symlink's encryption key, but we can continue
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* regardless of whether the key is available or not.
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*/
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err = fscrypt_get_encryption_info(inode);
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if (err)
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return ERR_PTR(err);
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has_key = fscrypt_has_encryption_key(inode);
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/*
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* For historical reasons, encrypted symlink targets are prefixed with
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* the ciphertext length, even though this is redundant with i_size.
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*/
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if (max_size < sizeof(*sd))
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return ERR_PTR(-EUCLEAN);
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sd = caddr;
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cstr.name = (unsigned char *)sd->encrypted_path;
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cstr.len = le16_to_cpu(sd->len);
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if (cstr.len == 0)
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return ERR_PTR(-EUCLEAN);
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if (cstr.len + sizeof(*sd) - 1 > max_size)
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return ERR_PTR(-EUCLEAN);
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err = fscrypt_fname_alloc_buffer(cstr.len, &pstr);
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if (err)
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return ERR_PTR(err);
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err = fscrypt_fname_disk_to_usr(inode, 0, 0, &cstr, &pstr);
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if (err)
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goto err_kfree;
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err = -EUCLEAN;
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if (pstr.name[0] == '\0')
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goto err_kfree;
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pstr.name[pstr.len] = '\0';
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/*
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* Cache decrypted symlink targets in i_link for later use. Don't cache
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* symlink targets encoded without the key, since those become outdated
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* once the key is added. This pairs with the READ_ONCE() above and in
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* the VFS path lookup code.
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*/
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if (!has_key ||
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cmpxchg_release(&inode->i_link, NULL, pstr.name) != NULL)
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set_delayed_call(done, kfree_link, pstr.name);
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return pstr.name;
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err_kfree:
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kfree(pstr.name);
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return ERR_PTR(err);
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}
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EXPORT_SYMBOL_GPL(fscrypt_get_symlink);
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/**
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* fscrypt_symlink_getattr() - set the correct st_size for encrypted symlinks
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* @path: the path for the encrypted symlink being queried
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* @stat: the struct being filled with the symlink's attributes
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*
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* Override st_size of encrypted symlinks to be the length of the decrypted
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* symlink target (or the no-key encoded symlink target, if the key is
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* unavailable) rather than the length of the encrypted symlink target. This is
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* necessary for st_size to match the symlink target that userspace actually
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* sees. POSIX requires this, and some userspace programs depend on it.
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*
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* This requires reading the symlink target from disk if needed, setting up the
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* inode's encryption key if possible, and then decrypting or encoding the
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* symlink target. This makes lstat() more heavyweight than is normally the
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* case. However, decrypted symlink targets will be cached in ->i_link, so
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* usually the symlink won't have to be read and decrypted again later if/when
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* it is actually followed, readlink() is called, or lstat() is called again.
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*
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* Return: 0 on success, -errno on failure
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*/
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int fscrypt_symlink_getattr(const struct path *path, struct kstat *stat)
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{
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struct dentry *dentry = path->dentry;
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struct inode *inode = d_inode(dentry);
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const char *link;
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DEFINE_DELAYED_CALL(done);
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/*
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* To get the symlink target that userspace will see (whether it's the
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* decrypted target or the no-key encoded target), we can just get it in
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* the same way the VFS does during path resolution and readlink().
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*/
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link = READ_ONCE(inode->i_link);
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if (!link) {
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link = inode->i_op->get_link(dentry, inode, &done);
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if (IS_ERR(link))
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return PTR_ERR(link);
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}
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stat->size = strlen(link);
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do_delayed_call(&done);
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return 0;
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}
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EXPORT_SYMBOL_GPL(fscrypt_symlink_getattr);
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