linuxdebug/fs/crypto/hooks.c

427 lines
13 KiB
C

// 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);
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),
&disk_link->len))
return -ENAMETOOLONG;
disk_link->len += sizeof(struct fscrypt_symlink_data);
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);
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(!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))
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) - 1 > 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);