Viewing: policy.c
// SPDX-License-Identifier: GPL-2.0
/*
* Encryption policy functions for per-file encryption support.
*
* Copyright (C) 2015, Google, Inc.
* Copyright (C) 2015, Motorola Mobility.
*
* Originally written by Michael Halcrow, 2015.
* Modified by Jaegeuk Kim, 2015.
* Modified by Eric Biggers, 2019 for v2 policy support.
*/
/*
* Linux commit 219d54332a09
* tags/v5.4
*/
#include <linux/random.h>
#include <linux/string.h>
#include <linux/mount.h>
#include <lustre_compat.h>
#include "llcrypt_private.h"
/**
* llcrypt_policies_equal - check whether two encryption policies are the same
*
* Return: %true if equal, else %false
*/
bool llcrypt_policies_equal(const union llcrypt_policy *policy1,
const union llcrypt_policy *policy2)
{
if (policy1->version != policy2->version)
return false;
return !memcmp(policy1, policy2, llcrypt_policy_size(policy1));
}
/**
* llcrypt_supported_policy - check whether an encryption policy is supported
*
* Given an encryption policy, check whether all its encryption modes and other
* settings are supported by this kernel. (But we don't currently don't check
* for crypto API support here, so attempting to use an algorithm not configured
* into the crypto API will still fail later.)
*
* Return: %true if supported, else %false
*/
bool llcrypt_supported_policy(const union llcrypt_policy *policy_u,
const struct inode *inode)
{
switch (policy_u->version) {
case LLCRYPT_POLICY_V1: {
const struct llcrypt_policy_v1 *policy = &policy_u->v1;
if (!llcrypt_valid_enc_modes(policy->contents_encryption_mode,
policy->filenames_encryption_mode)) {
llcrypt_warn(inode,
"Unsupported encryption modes (contents %d, filenames %d)",
policy->contents_encryption_mode,
policy->filenames_encryption_mode);
return false;
}
if (policy->flags & ~LLCRYPT_POLICY_FLAGS_VALID) {
llcrypt_warn(inode,
"Unsupported encryption flags (0x%02x)",
policy->flags);
return false;
}
return true;
}
case LLCRYPT_POLICY_V2: {
const struct llcrypt_policy_v2 *policy = &policy_u->v2;
if (!llcrypt_valid_enc_modes(policy->contents_encryption_mode,
policy->filenames_encryption_mode)) {
llcrypt_warn(inode,
"Unsupported encryption modes (contents %d, filenames %d)",
policy->contents_encryption_mode,
policy->filenames_encryption_mode);
return false;
}
if (policy->flags & ~LLCRYPT_POLICY_FLAGS_VALID) {
llcrypt_warn(inode,
"Unsupported encryption flags (0x%02x)",
policy->flags);
return false;
}
if (memchr_inv(policy->__reserved, 0,
sizeof(policy->__reserved))) {
llcrypt_warn(inode,
"Reserved bits set in encryption policy");
return false;
}
return true;
}
}
return false;
}
/**
* llcrypt_new_context_from_policy - create a new llcrypt_context from a policy
*
* Create an llcrypt_context for an inode that is being assigned the given
* encryption policy. A new nonce is randomly generated.
*
* Return: the size of the new context in bytes.
*/
static int llcrypt_new_context_from_policy(union llcrypt_context *ctx_u,
const union llcrypt_policy *policy_u)
{
memset(ctx_u, 0, sizeof(*ctx_u));
switch (policy_u->version) {
case LLCRYPT_POLICY_V1: {
const struct llcrypt_policy_v1 *policy = &policy_u->v1;
struct llcrypt_context_v1 *ctx = &ctx_u->v1;
ctx->version = LLCRYPT_CONTEXT_V1;
ctx->contents_encryption_mode =
policy->contents_encryption_mode;
ctx->filenames_encryption_mode =
policy->filenames_encryption_mode;
ctx->flags = policy->flags;
memcpy(ctx->master_key_descriptor,
policy->master_key_descriptor,
sizeof(ctx->master_key_descriptor));
get_random_bytes(ctx->nonce, sizeof(ctx->nonce));
return sizeof(*ctx);
}
case LLCRYPT_POLICY_V2: {
const struct llcrypt_policy_v2 *policy = &policy_u->v2;
struct llcrypt_context_v2 *ctx = &ctx_u->v2;
ctx->version = LLCRYPT_CONTEXT_V2;
ctx->contents_encryption_mode =
policy->contents_encryption_mode;
ctx->filenames_encryption_mode =
policy->filenames_encryption_mode;
ctx->flags = policy->flags;
memcpy(ctx->master_key_identifier,
policy->master_key_identifier,
sizeof(ctx->master_key_identifier));
get_random_bytes(ctx->nonce, sizeof(ctx->nonce));
return sizeof(*ctx);
}
}
BUG();
}
/**
* llcrypt_policy_from_context - convert an llcrypt_context to an llcrypt_policy
*
* Given an llcrypt_context, build the corresponding llcrypt_policy.
*
* Return: 0 on success, or -EINVAL if the llcrypt_context has an unrecognized
* version number or size.
*
* This does *not* validate the settings within the policy itself, e.g. the
* modes, flags, and reserved bits. Use llcrypt_supported_policy() for that.
*/
int llcrypt_policy_from_context(union llcrypt_policy *policy_u,
const union llcrypt_context *ctx_u,
int ctx_size)
{
memset(policy_u, 0, sizeof(*policy_u));
if (ctx_size <= 0 || ctx_size != llcrypt_context_size(ctx_u))
return -EINVAL;
switch (ctx_u->version) {
case LLCRYPT_CONTEXT_V1: {
const struct llcrypt_context_v1 *ctx = &ctx_u->v1;
struct llcrypt_policy_v1 *policy = &policy_u->v1;
policy->version = LLCRYPT_POLICY_V1;
policy->contents_encryption_mode =
ctx->contents_encryption_mode;
policy->filenames_encryption_mode =
ctx->filenames_encryption_mode;
policy->flags = ctx->flags;
memcpy(policy->master_key_descriptor,
ctx->master_key_descriptor,
sizeof(policy->master_key_descriptor));
return 0;
}
case LLCRYPT_CONTEXT_V2: {
const struct llcrypt_context_v2 *ctx = &ctx_u->v2;
struct llcrypt_policy_v2 *policy = &policy_u->v2;
policy->version = LLCRYPT_POLICY_V2;
policy->contents_encryption_mode =
ctx->contents_encryption_mode;
policy->filenames_encryption_mode =
ctx->filenames_encryption_mode;
policy->flags = ctx->flags;
memcpy(policy->__reserved, ctx->__reserved,
sizeof(policy->__reserved));
memcpy(policy->master_key_identifier,
ctx->master_key_identifier,
sizeof(policy->master_key_identifier));
return 0;
}
}
/* unreachable */
return -EINVAL;
}
/* Retrieve an inode's encryption policy */
static int llcrypt_get_policy(struct inode *inode, union llcrypt_policy *policy)
{
const struct llcrypt_info *ci;
union llcrypt_context ctx;
struct lustre_sb_info *lsi = s2lsi(inode->i_sb);
int ret;
ci = (struct llcrypt_info *)READ_ONCE(llcrypt_info_nocast(inode));
if (ci) {
/* key available, use the cached policy */
*policy = ci->ci_policy;
return 0;
}
if (!IS_ENCRYPTED(inode))
return -ENODATA;
if (!lsi)
return -ENODATA;
ret = lsi->lsi_cop->get_context(inode, &ctx, sizeof(ctx));
if (ret < 0)
return (ret == -ERANGE) ? -EINVAL : ret;
return llcrypt_policy_from_context(policy, &ctx, ret);
}
static int set_encryption_policy(struct inode *inode,
const union llcrypt_policy *policy)
{
union llcrypt_context ctx;
int ctxsize;
struct lustre_sb_info *lsi = s2lsi(inode->i_sb);
int err;
if (!llcrypt_supported_policy(policy, inode))
return -EINVAL;
switch (policy->version) {
case LLCRYPT_POLICY_V1:
/*
* The original encryption policy version provided no way of
* verifying that the correct master key was supplied, which was
* insecure in scenarios where multiple users have access to the
* same encrypted files (even just read-only access). The new
* encryption policy version fixes this and also implies use of
* an improved key derivation function and allows non-root users
* to securely remove keys. So as long as compatibility with
* old kernels isn't required, it is recommended to use the new
* policy version for all new encrypted directories.
*/
pr_warn_once("%s (pid %d) is setting deprecated v1 encryption policy; recommend upgrading to v2.\n",
current->comm, current->pid);
break;
case LLCRYPT_POLICY_V2:
err = llcrypt_verify_key_added(inode->i_sb,
policy->v2.master_key_identifier);
if (err)
return err;
break;
default:
WARN_ON(1);
return -EINVAL;
}
ctxsize = llcrypt_new_context_from_policy(&ctx, policy);
if (!lsi)
return -EINVAL;
return lsi->lsi_cop->set_context(inode, &ctx, ctxsize, NULL);
}
/* Tell if an inode's encryption policy has filename encryption */
bool llcrypt_policy_has_filename_enc(struct inode *inode)
{
union llcrypt_policy policy;
int err;
err = llcrypt_get_policy(inode, &policy);
if (err)
return true;
if ((policy.version == LLCRYPT_POLICY_V1 &&
policy.v1.filenames_encryption_mode == LLCRYPT_MODE_NULL) ||
(policy.version == LLCRYPT_POLICY_V2 &&
policy.v2.filenames_encryption_mode == LLCRYPT_MODE_NULL))
return false;
return true;
}
EXPORT_SYMBOL(llcrypt_policy_has_filename_enc);
int llcrypt_ioctl_set_policy(struct file *filp, const void __user *arg)
{
union llcrypt_policy policy;
union llcrypt_policy existing_policy;
struct inode *inode = file_inode(filp);
struct lustre_sb_info *lsi = s2lsi(inode->i_sb);
u8 version;
int size;
int ret;
if (get_user(policy.version, (const u8 __user *)arg))
return -EFAULT;
size = llcrypt_policy_size(&policy);
if (size <= 0)
return -EINVAL;
/*
* We should just copy the remaining 'size - 1' bytes here, but a
* bizarre bug in gcc 7 and earlier (fixed by gcc r255731) causes gcc to
* think that size can be 0 here (despite the check above!) *and* that
* it's a compile-time constant. Thus it would think copy_from_user()
* is passed compile-time constant ULONG_MAX, causing the compile-time
* buffer overflow check to fail, breaking the build. This only occurred
* when building an i386 kernel with -Os and branch profiling enabled.
*
* Work around it by just copying the first byte again...
*/
version = policy.version;
if (copy_from_user(&policy, arg, size))
return -EFAULT;
policy.version = version;
/* Force file/directory name encryption policy to null if
* LSI_FILENAME_ENC flag is not set on sb.
* This allows enabling filename encryption separately from data
* encryption, and can be useful for interoperability with
* encryption-unaware clients.
*/
if (!(lsi->lsi_flags & LSI_FILENAME_ENC)) {
CWARN("inode %lu: forcing policy filenames_encryption_mode to null\n",
inode->i_ino);
cfs_tty_write_msg("\n\nForcing policy filenames_encryption_mode to null.\n\n");
switch (policy.version) {
case LLCRYPT_POLICY_V1:
policy.v1.filenames_encryption_mode = LLCRYPT_MODE_NULL;
break;
case LLCRYPT_POLICY_V2:
policy.v2.filenames_encryption_mode = LLCRYPT_MODE_NULL;
break;
}
}
if (!inode_owner_or_capable(&nop_mnt_idmap, inode))
return -EACCES;
ret = mnt_want_write_file(filp);
if (ret)
return ret;
inode_lock(inode);
ret = llcrypt_get_policy(inode, &existing_policy);
if (ret == -ENODATA) {
struct lustre_sb_info *lsi = s2lsi(inode->i_sb);
if (!S_ISDIR(inode->i_mode))
ret = -ENOTDIR;
else if (IS_DEADDIR(inode))
ret = -ENOENT;
else if (lsi && !lsi->lsi_cop->empty_dir(inode))
ret = -ENOTEMPTY;
else
ret = set_encryption_policy(inode, &policy);
} else if (ret == -EINVAL ||
(ret == 0 && !llcrypt_policies_equal(&policy,
&existing_policy))) {
/* The file already uses a different encryption policy. */
ret = -EEXIST;
}
inode_unlock(inode);
mnt_drop_write_file(filp);
return ret;
}
EXPORT_SYMBOL(llcrypt_ioctl_set_policy);
/* Original ioctl version; can only get the original policy version */
int llcrypt_ioctl_get_policy(struct file *filp, void __user *arg)
{
union llcrypt_policy policy;
int err;
err = llcrypt_get_policy(file_inode(filp), &policy);
if (err)
return err;
if (policy.version != LLCRYPT_POLICY_V1)
return -EINVAL;
if (copy_to_user(arg, &policy, sizeof(policy.v1)))
return -EFAULT;
return 0;
}
EXPORT_SYMBOL(llcrypt_ioctl_get_policy);
/* Valid filenames_encryption_mode associated with contents_encryption_mode,
* as imposed by llcrypt_valid_enc_modes()
*/
static inline u8 contents2filenames_encmode(u8 contents_encryption_mode)
{
if (contents_encryption_mode == LLCRYPT_MODE_AES_128_CBC)
return LLCRYPT_MODE_AES_128_CTS;
if (contents_encryption_mode == LLCRYPT_MODE_AES_256_XTS)
return LLCRYPT_MODE_AES_256_CTS;
if (contents_encryption_mode == LLCRYPT_MODE_ADIANTUM)
return LLCRYPT_MODE_ADIANTUM;
return LLCRYPT_MODE_NULL;
}
/* Extended ioctl version; can get policies of any version */
int llcrypt_ioctl_get_policy_ex(struct file *filp, void __user *uarg)
{
struct llcrypt_get_policy_ex_arg arg;
union llcrypt_policy *policy = (union llcrypt_policy *)&arg.policy;
size_t policy_size;
struct inode *inode = file_inode(filp);
int err;
/* arg is policy_size, then policy */
BUILD_BUG_ON(offsetof(typeof(arg), policy_size) != 0);
BUILD_BUG_ON(offsetofend(typeof(arg), policy_size) !=
offsetof(typeof(arg), policy));
BUILD_BUG_ON(sizeof(arg.policy) != sizeof(*policy));
if (copy_from_user(&arg, uarg, sizeof(arg.policy_size)))
return -EFAULT;
err = llcrypt_get_policy(file_inode(filp), policy);
if (err)
return err;
policy_size = llcrypt_policy_size(policy);
if (policy_size > arg.policy_size)
return -EOVERFLOW;
arg.policy_size = policy_size;
/* Do not return null filenames_encryption_mode to userspace, as it is
* unknown. Instead, return valid mode associated with
* contents_encryption_mode, as imposed by llcrypt_valid_enc_modes().
*/
switch (policy->version) {
case LLCRYPT_POLICY_V1:
if (policy->v1.filenames_encryption_mode == LLCRYPT_MODE_NULL) {
policy->v1.filenames_encryption_mode =
contents2filenames_encmode(
policy->v1.contents_encryption_mode);
CWARN("inode %lu: returning policy filenames_encryption_mode as %d, but is in fact null\n",
inode->i_ino,
policy->v1.filenames_encryption_mode);
}
break;
case LLCRYPT_POLICY_V2:
if (policy->v2.filenames_encryption_mode == LLCRYPT_MODE_NULL) {
policy->v2.filenames_encryption_mode =
contents2filenames_encmode(
policy->v2.contents_encryption_mode);
CWARN("inode %lu: returning policy filenames_encryption_mode as %d, but is in fact null\n",
inode->i_ino,
policy->v2.filenames_encryption_mode);
}
break;
}
if (copy_to_user(uarg, &arg, sizeof(arg.policy_size) + policy_size))
return -EFAULT;
return 0;
}
EXPORT_SYMBOL_GPL(llcrypt_ioctl_get_policy_ex);
/**
* llcrypt_has_permitted_context() - is a file's encryption policy permitted
* within its directory?
*
* @parent: inode for parent directory
* @child: inode for file being looked up, opened, or linked into @parent
*
* Filesystems must call this before permitting access to an inode in a
* situation where the parent directory is encrypted (either before allowing
* ->lookup() to succeed, or for a regular file before allowing it to be opened)
* and before any operation that involves linking an inode into an encrypted
* directory, including link, rename, and cross rename. It enforces the
* constraint that within a given encrypted directory tree, all files use the
* same encryption policy. The pre-access check is needed to detect potentially
* malicious offline violations of this constraint, while the link and rename
* checks are needed to prevent online violations of this constraint.
*
* Return: 1 if permitted, 0 if forbidden.
*/
int llcrypt_has_permitted_context(struct inode *parent, struct inode *child)
{
union llcrypt_policy parent_policy, child_policy;
int err;
/* No restrictions on file types which are never encrypted */
if (!S_ISREG(child->i_mode) && !S_ISDIR(child->i_mode) &&
!S_ISLNK(child->i_mode))
return 1;
/* No restrictions if the parent directory is unencrypted */
if (!IS_ENCRYPTED(parent))
return 1;
/* Encrypted directories must not contain unencrypted files */
if (!IS_ENCRYPTED(child))
return 0;
/*
* Both parent and child are encrypted, so verify they use the same
* encryption policy. Compare the llcrypt_info structs if the keys are
* available, otherwise retrieve and compare the llcrypt_contexts.
*
* Note that the llcrypt_context retrieval will be required frequently
* when accessing an encrypted directory tree without the key.
* Performance-wise this is not a big deal because we already don't
* really optimize for file access without the key (to the extent that
* such access is even possible), given that any attempted access
* already causes a llcrypt_context retrieval and keyring search.
*
* In any case, if an unexpected error occurs, fall back to "forbidden".
*/
err = llcrypt_get_encryption_info(parent);
if (err)
return 0;
err = llcrypt_get_encryption_info(child);
if (err)
return 0;
err = llcrypt_get_policy(parent, &parent_policy);
if (err)
return 0;
err = llcrypt_get_policy(child, &child_policy);
if (err)
return 0;
return llcrypt_policies_equal(&parent_policy, &child_policy);
}
EXPORT_SYMBOL(llcrypt_has_permitted_context);
/**
* llcrypt_inherit_context() - Sets a child context from its parent
* @parent: Parent inode from which the context is inherited.
* @child: Child inode that inherits the context from @parent.
* @fs_data: private data given by FS.
* @preload: preload child crypt info if true
*
* Return: 0 on success, -errno on failure
*/
int llcrypt_inherit_context(struct inode *parent, struct inode *child,
void *fs_data, bool preload)
{
union llcrypt_context ctx;
int ctxsize;
struct llcrypt_info *ci;
struct lustre_sb_info *lsi = s2lsi(parent->i_sb);
int res;
res = llcrypt_get_encryption_info(parent);
if (res < 0)
return res;
ci = (struct llcrypt_info *)READ_ONCE(llcrypt_info_nocast(parent));
if (ci == NULL)
return -ENOKEY;
if (!lsi)
return -ENOKEY;
ctxsize = llcrypt_new_context_from_policy(&ctx, &ci->ci_policy);
BUILD_BUG_ON(sizeof(ctx) != LLCRYPT_SET_CONTEXT_MAX_SIZE);
res = lsi->lsi_cop->set_context(child, &ctx, ctxsize, fs_data);
if (res)
return res;
return preload ? llcrypt_get_encryption_info(child): 0;
}
EXPORT_SYMBOL(llcrypt_inherit_context);
