path: root/fs/crypto/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.
 */

#include <linux/random.h>
#include <linux/string.h>
#include <linux/mount.h>
#include "fscrypt_private.h"

/**
 * fscrypt_policies_equal - check whether two encryption policies are the same
 *
 * Return: %true if equal, else %false
 */
bool fscrypt_policies_equal(const union fscrypt_policy *policy1,
			    const union fscrypt_policy *policy2)
{
	if (policy1->version != policy2->version)
		return false;

	return !memcmp(policy1, policy2, fscrypt_policy_size(policy1));
}

static bool fscrypt_valid_enc_modes(u32 contents_mode, u32 filenames_mode)
{
	if (contents_mode == FSCRYPT_MODE_AES_256_XTS &&
	    filenames_mode == FSCRYPT_MODE_AES_256_CTS)
		return true;

	if (contents_mode == FSCRYPT_MODE_AES_128_CBC &&
	    filenames_mode == FSCRYPT_MODE_AES_128_CTS)
		return true;

	if (contents_mode == FSCRYPT_MODE_ADIANTUM &&
	    filenames_mode == FSCRYPT_MODE_ADIANTUM)
		return true;

	return false;
}

static bool supported_direct_key_modes(const struct inode *inode,
				       u32 contents_mode, u32 filenames_mode)
{
	const struct fscrypt_mode *mode;

	if (contents_mode != filenames_mode) {
		fscrypt_warn(inode,
			     "Direct key flag not allowed with different contents and filenames modes");
		return false;
	}
	mode = &fscrypt_modes[contents_mode];

	if (mode->ivsize < offsetofend(union fscrypt_iv, nonce)) {
		fscrypt_warn(inode, "Direct key flag not allowed with %s",
			     mode->friendly_name);
		return false;
	}
	return true;
}

static bool supported_iv_ino_lblk_64_policy(
					const struct fscrypt_policy_v2 *policy,
					const struct inode *inode)
{
	struct super_block *sb = inode->i_sb;
	int ino_bits = 64, lblk_bits = 64;

	if (policy->flags & FSCRYPT_POLICY_FLAG_DIRECT_KEY) {
		fscrypt_warn(inode,
			     "The DIRECT_KEY and IV_INO_LBLK_64 flags are mutually exclusive");
		return false;
	}
	/*
	 * It's unsafe to include inode numbers in the IVs if the filesystem can
	 * potentially renumber inodes, e.g. via filesystem shrinking.
	 */
	if (!sb->s_cop->has_stable_inodes ||
	    !sb->s_cop->has_stable_inodes(sb)) {
		fscrypt_warn(inode,
			     "Can't use IV_INO_LBLK_64 policy on filesystem '%s' because it doesn't have stable inode numbers",
			     sb->s_id);
		return false;
	}
	if (sb->s_cop->get_ino_and_lblk_bits)
		sb->s_cop->get_ino_and_lblk_bits(sb, &ino_bits, &lblk_bits);
	if (ino_bits > 32 || lblk_bits > 32) {
		fscrypt_warn(inode,
			     "Can't use IV_INO_LBLK_64 policy on filesystem '%s' because it doesn't use 32-bit inode and block numbers",
			     sb->s_id);
		return false;
	}
	return true;
}

static bool fscrypt_supported_v1_policy(const struct fscrypt_policy_v1 *policy,
					const struct inode *inode)
{
	if (!fscrypt_valid_enc_modes(policy->contents_encryption_mode,
				     policy->filenames_encryption_mode)) {
		fscrypt_warn(inode,
			     "Unsupported encryption modes (contents %d, filenames %d)",
			     policy->contents_encryption_mode,
			     policy->filenames_encryption_mode);
		return false;
	}

	if (policy->flags & ~(FSCRYPT_POLICY_FLAGS_PAD_MASK |
			      FSCRYPT_POLICY_FLAG_DIRECT_KEY)) {
		fscrypt_warn(inode, "Unsupported encryption flags (0x%02x)",
			     policy->flags);
		return false;
	}

	if ((policy->flags & FSCRYPT_POLICY_FLAG_DIRECT_KEY) &&
	    !supported_direct_key_modes(inode, policy->contents_encryption_mode,
					policy->filenames_encryption_mode))
		return false;

	if (IS_CASEFOLDED(inode)) {
		/* With v1, there's no way to derive dirhash keys. */
		fscrypt_warn(inode,
			     "v1 policies can't be used on casefolded directories");
		return false;
	}

	return true;
}

static bool fscrypt_supported_v2_policy(const struct fscrypt_policy_v2 *policy,
					const struct inode *inode)
{
	if (!fscrypt_valid_enc_modes(policy->contents_encryption_mode,
				     policy->filenames_encryption_mode)) {
		fscrypt_warn(inode,
			     "Unsupported encryption modes (contents %d, filenames %d)",
			     policy->contents_encryption_mode,
			     policy->filenames_encryption_mode);
		return false;
	}

	if (policy->flags & ~FSCRYPT_POLICY_FLAGS_VALID) {
		fscrypt_warn(inode, "Unsupported encryption flags (0x%02x)",
			     policy->flags);
		return false;
	}

	if ((policy->flags & FSCRYPT_POLICY_FLAG_DIRECT_KEY) &&
	    !supported_direct_key_modes(inode, policy->contents_encryption_mode,
					policy->filenames_encryption_mode))
		return false;

	if ((policy->flags & FSCRYPT_POLICY_FLAG_IV_INO_LBLK_64) &&
	    !supported_iv_ino_lblk_64_policy(policy, inode))
		return false;

	if (memchr_inv(policy->__reserved, 0, sizeof(policy->__reserved))) {
		fscrypt_warn(inode, "Reserved bits set in encryption policy");
		return false;
	}

	return true;
}

/**
 * fscrypt_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 on the given inode.  (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 fscrypt_supported_policy(const union fscrypt_policy *policy_u,
			      const struct inode *inode)
{
	switch (policy_u->version) {
	case FSCRYPT_POLICY_V1:
		return fscrypt_supported_v1_policy(&policy_u->v1, inode);
	case FSCRYPT_POLICY_V2:
		return fscrypt_supported_v2_policy(&policy_u->v2, inode);
	}
	return false;
}

/**
 * fscrypt_new_context_from_policy - create a new fscrypt_context from a policy
 *
 * Create an fscrypt_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 fscrypt_new_context_from_policy(union fscrypt_context *ctx_u,
					   const union fscrypt_policy *policy_u)
{
	memset(ctx_u, 0, sizeof(*ctx_u));

	switch (policy_u->version) {
	case FSCRYPT_POLICY_V1: {
		const struct fscrypt_policy_v1 *policy = &policy_u->v1;
		struct fscrypt_context_v1 *ctx = &ctx_u->v1;

		ctx->version = FSCRYPT_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 FSCRYPT_POLICY_V2: {
		const struct fscrypt_policy_v2 *policy = &policy_u->v2;
		struct fscrypt_context_v2 *ctx = &ctx_u->v2;

		ctx->version = FSCRYPT_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