fs/crypto/policy.c - arm/linux - Git at Google

 // SPDX-License-Identifier: GPL-2.0
 /*
  * Encryption policy functions for per-file encryption support.
  *
  * Copyright (C) 2015, Google, Inc.
  * Copyright (C) 2015, Motorola Mobility.
  *
  * Written by Michael Halcrow, 2015.
  * Modified by Jaegeuk Kim, 2015.
  */

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

 /*
  * check whether an encryption policy is consistent with an encryption context
  */
 static bool is_encryption_context_consistent_with_policy(
 				const struct fscrypt_context *ctx,
 				const struct fscrypt_policy *policy)
 {
 	return memcmp(ctx->master_key_descriptor, policy->master_key_descriptor,
 		      FS_KEY_DESCRIPTOR_SIZE) == 0 &&
 		(ctx->flags == policy->flags) &&
 		(ctx->contents_encryption_mode ==
 		 policy->contents_encryption_mode) &&
 		(ctx->filenames_encryption_mode ==
 		 policy->filenames_encryption_mode);
 }

 static int create_encryption_context_from_policy(struct inode *inode,
 				const struct fscrypt_policy *policy)
 {
 	struct fscrypt_context ctx;

 	ctx.format = FS_ENCRYPTION_CONTEXT_FORMAT_V1;
 	memcpy(ctx.master_key_descriptor, policy->master_key_descriptor,
 					FS_KEY_DESCRIPTOR_SIZE);

 	if (!fscrypt_valid_enc_modes(policy->contents_encryption_mode,
 				     policy->filenames_encryption_mode))
 		return -EINVAL;

 	if (policy->flags & ~FS_POLICY_FLAGS_VALID)
 		return -EINVAL;

 	ctx.contents_encryption_mode = policy->contents_encryption_mode;
 	ctx.filenames_encryption_mode = policy->filenames_encryption_mode;
 	ctx.flags = policy->flags;
 	BUILD_BUG_ON(sizeof(ctx.nonce) != FS_KEY_DERIVATION_NONCE_SIZE);
 	get_random_bytes(ctx.nonce, FS_KEY_DERIVATION_NONCE_SIZE);

 	return inode->i_sb->s_cop->set_context(inode, &ctx, sizeof(ctx), NULL);
 }

 int fscrypt_ioctl_set_policy(struct file *filp, const void __user *arg)
 {
 	struct fscrypt_policy policy;
 	struct inode *inode = file_inode(filp);
 	int ret;
 	struct fscrypt_context ctx;

 	if (copy_from_user(&policy, arg, sizeof(policy)))
 		return -EFAULT;

 	if (!inode_owner_or_capable(inode))
 		return -EACCES;

 	if (policy.version != 0)
 		return -EINVAL;

 	ret = mnt_want_write_file(filp);
 	if (ret)
 		return ret;

 	inode_lock(inode);

 	ret = inode->i_sb->s_cop->get_context(inode, &ctx, sizeof(ctx));
 	if (ret == -ENODATA) {
 		if (!S_ISDIR(inode->i_mode))
 			ret = -ENOTDIR;
 		else if (!inode->i_sb->s_cop->empty_dir(inode))
 			ret = -ENOTEMPTY;
 		else
 			ret = create_encryption_context_from_policy(inode,
 								    &policy);
 	} else if (ret == sizeof(ctx) &&
 		   is_encryption_context_consistent_with_policy(&ctx,
 								&policy)) {
 		/* The file already uses the same encryption policy. */
 		ret = 0;
 	} else if (ret >= 0 || ret == -ERANGE) {
 		/* The file already uses a different encryption policy. */
 		ret = -EEXIST;
 	}

 	inode_unlock(inode);

 	mnt_drop_write_file(filp);
 	return ret;
 }
 EXPORT_SYMBOL(fscrypt_ioctl_set_policy);

 int fscrypt_ioctl_get_policy(struct file *filp, void __user *arg)
 {
 	struct inode *inode = file_inode(filp);
 	struct fscrypt_context ctx;
 	struct fscrypt_policy policy;
 	int res;

 	if (!inode->i_sb->s_cop->is_encrypted(inode))
 		return -ENODATA;

 	res = inode->i_sb->s_cop->get_context(inode, &ctx, sizeof(ctx));
 	if (res < 0 && res != -ERANGE)
 		return res;
 	if (res != sizeof(ctx))
 		return -EINVAL;
 	if (ctx.format != FS_ENCRYPTION_CONTEXT_FORMAT_V1)
 		return -EINVAL;

 	policy.version = 0;
 	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,
 				FS_KEY_DESCRIPTOR_SIZE);

 	if (copy_to_user(arg, &policy, sizeof(policy)))
 		return -EFAULT;
 	return 0;
 }
 EXPORT_SYMBOL(fscrypt_ioctl_get_policy);

 /**
  * fscrypt_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.  If forbidden, the caller must fail
  * the filesystem operation with EPERM.
  */
 int fscrypt_has_permitted_context(struct inode *parent, struct inode *child)
 {
 	const struct fscrypt_operations *cops = parent->i_sb->s_cop;
 	const struct fscrypt_info *parent_ci, *child_ci;
 	struct fscrypt_context parent_ctx, child_ctx;
 	int res;

 	/* 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 (!cops->is_encrypted(parent))
 		return 1;

 	/* Encrypted directories must not contain unencrypted files */
 	if (!cops->is_encrypted(child))
 		return 0;

 	/*
 	 * Both parent and child are encrypted, so verify they use the same
 	 * encryption policy.  Compare the fscrypt_info structs if the keys are
 	 * available, otherwise retrieve and compare the fscrypt_contexts.
 	 *
 	 * Note that the fscrypt_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 fscrypt_context retrieval and keyring search.
 	 *
 	 * In any case, if an unexpected error occurs, fall back to "forbidden".
 	 */

 	res = fscrypt_get_encryption_info(parent);
 	if (res)
 		return 0;
 	res = fscrypt_get_encryption_info(child);
 	if (res)
 		return 0;
 	parent_ci = parent->i_crypt_info;
 	child_ci = child->i_crypt_info;

 	if (parent_ci && child_ci) {
 		return memcmp(parent_ci->ci_master_key, child_ci->ci_master_key,
 			      FS_KEY_DESCRIPTOR_SIZE) == 0 &&
 			(parent_ci->ci_data_mode == child_ci->ci_data_mode) &&
 			(parent_ci->ci_filename_mode ==
 			 child_ci->ci_filename_mode) &&
 			(parent_ci->ci_flags == child_ci->ci_flags);
 	}

 	res = cops->get_context(parent, &parent_ctx, sizeof(parent_ctx));
 	if (res != sizeof(parent_ctx))
 		return 0;

 	res = cops->get_context(child, &child_ctx, sizeof(child_ctx));
 	if (res != sizeof(child_ctx))
 		return 0;

 	return memcmp(parent_ctx.master_key_descriptor,
 		      child_ctx.master_key_descriptor,
 		      FS_KEY_DESCRIPTOR_SIZE) == 0 &&
 		(parent_ctx.contents_encryption_mode ==
 		 child_ctx.contents_encryption_mode) &&
 		(parent_ctx.filenames_encryption_mode ==
 		 child_ctx.filenames_encryption_mode) &&
 		(parent_ctx.flags == child_ctx.flags);
 }
 EXPORT_SYMBOL(fscrypt_has_permitted_context);

 /**
  * fscrypt_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 i_crypt_info if true
  *
  * Return: 0 on success, -errno on failure
  */
 int fscrypt_inherit_context(struct inode *parent, struct inode *child,
 						void *fs_data, bool preload)
 {
 	struct fscrypt_context ctx;
 	struct fscrypt_info *ci;
 	int res;

 	res = fscrypt_get_encryption_info(parent);
 	if (res < 0)
 		return res;

 	ci = parent->i_crypt_info;
 	if (ci == NULL)
 		return -ENOKEY;

 	ctx.format = FS_ENCRYPTION_CONTEXT_FORMAT_V1;
 	ctx.contents_encryption_mode = ci->ci_data_mode;
 	ctx.filenames_encryption_mode = ci->ci_filename_mode;
 	ctx.flags = ci->ci_flags;
 	memcpy(ctx.master_key_descriptor, ci->ci_master_key,
 	       FS_KEY_DESCRIPTOR_SIZE);
 	get_random_bytes(ctx.nonce, FS_KEY_DERIVATION_NONCE_SIZE);
 	BUILD_BUG_ON(sizeof(ctx) != FSCRYPT_SET_CONTEXT_MAX_SIZE);
 	res = parent->i_sb->s_cop->set_context(child, &ctx,
 						sizeof(ctx), fs_data);
 	if (res)
 		return res;
 	return preload ? fscrypt_get_encryption_info(child): 0;
 }
 EXPORT_SYMBOL(fscrypt_inherit_context);
	// SPDX-License-Identifier: GPL-2.0
	/*
	* Encryption policy functions for per-file encryption support.
	*
	* Copyright (C) 2015, Google, Inc.
	* Copyright (C) 2015, Motorola Mobility.
	*
	* Written by Michael Halcrow, 2015.
	* Modified by Jaegeuk Kim, 2015.
	*/

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

	/*
	* check whether an encryption policy is consistent with an encryption context
	*/
	static bool is_encryption_context_consistent_with_policy(
	const struct fscrypt_context *ctx,
	const struct fscrypt_policy *policy)
	{
	return memcmp(ctx->master_key_descriptor, policy->master_key_descriptor,
	FS_KEY_DESCRIPTOR_SIZE) == 0 &&
	(ctx->flags == policy->flags) &&
	(ctx->contents_encryption_mode ==
	policy->contents_encryption_mode) &&
	(ctx->filenames_encryption_mode ==
	policy->filenames_encryption_mode);
	}

	static int create_encryption_context_from_policy(struct inode *inode,
	const struct fscrypt_policy *policy)
	{
	struct fscrypt_context ctx;

	ctx.format = FS_ENCRYPTION_CONTEXT_FORMAT_V1;
	memcpy(ctx.master_key_descriptor, policy->master_key_descriptor,
	FS_KEY_DESCRIPTOR_SIZE);

	if (!fscrypt_valid_enc_modes(policy->contents_encryption_mode,
	policy->filenames_encryption_mode))
	return -EINVAL;

	if (policy->flags & ~FS_POLICY_FLAGS_VALID)
	return -EINVAL;

	ctx.contents_encryption_mode = policy->contents_encryption_mode;
	ctx.filenames_encryption_mode = policy->filenames_encryption_mode;
	ctx.flags = policy->flags;
	BUILD_BUG_ON(sizeof(ctx.nonce) != FS_KEY_DERIVATION_NONCE_SIZE);
	get_random_bytes(ctx.nonce, FS_KEY_DERIVATION_NONCE_SIZE);

	return inode->i_sb->s_cop->set_context(inode, &ctx, sizeof(ctx), NULL);
	}

	int fscrypt_ioctl_set_policy(struct file filp, const void __user arg)
	{
	struct fscrypt_policy policy;
	struct inode *inode = file_inode(filp);
	int ret;
	struct fscrypt_context ctx;

	if (copy_from_user(&policy, arg, sizeof(policy)))
	return -EFAULT;

	if (!inode_owner_or_capable(inode))
	return -EACCES;

	if (policy.version != 0)
	return -EINVAL;

	ret = mnt_want_write_file(filp);
	if (ret)
	return ret;

	inode_lock(inode);

	ret = inode->i_sb->s_cop->get_context(inode, &ctx, sizeof(ctx));
	if (ret == -ENODATA) {
	if (!S_ISDIR(inode->i_mode))
	ret = -ENOTDIR;
	else if (!inode->i_sb->s_cop->empty_dir(inode))
	ret = -ENOTEMPTY;
	else
	ret = create_encryption_context_from_policy(inode,
	&policy);
	} else if (ret == sizeof(ctx) &&
	is_encryption_context_consistent_with_policy(&ctx,
	&policy)) {
	/* The file already uses the same encryption policy. */
	ret = 0;
	} else if (ret >= 0 \|\| ret == -ERANGE) {
	/* The file already uses a different encryption policy. */
	ret = -EEXIST;
	}

	inode_unlock(inode);

	mnt_drop_write_file(filp);
	return ret;
	}
	EXPORT_SYMBOL(fscrypt_ioctl_set_policy);

	int fscrypt_ioctl_get_policy(struct file filp, void __user arg)
	{
	struct inode *inode = file_inode(filp);
	struct fscrypt_context ctx;
	struct fscrypt_policy policy;
	int res;

	if (!inode->i_sb->s_cop->is_encrypted(inode))
	return -ENODATA;

	res = inode->i_sb->s_cop->get_context(inode, &ctx, sizeof(ctx));
	if (res < 0 && res != -ERANGE)
	return res;
	if (res != sizeof(ctx))
	return -EINVAL;
	if (ctx.format != FS_ENCRYPTION_CONTEXT_FORMAT_V1)
	return -EINVAL;

	policy.version = 0;
	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,
	FS_KEY_DESCRIPTOR_SIZE);

	if (copy_to_user(arg, &policy, sizeof(policy)))
	return -EFAULT;
	return 0;
	}
	EXPORT_SYMBOL(fscrypt_ioctl_get_policy);

	/**
	* fscrypt_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. If forbidden, the caller must fail
	* the filesystem operation with EPERM.
	*/
	int fscrypt_has_permitted_context(struct inode parent, struct inode child)
	{
	const struct fscrypt_operations *cops = parent->i_sb->s_cop;
	const struct fscrypt_info parent_ci, child_ci;
	struct fscrypt_context parent_ctx, child_ctx;
	int res;

	/* 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 (!cops->is_encrypted(parent))
	return 1;

	/* Encrypted directories must not contain unencrypted files */
	if (!cops->is_encrypted(child))
	return 0;

	/*
	* Both parent and child are encrypted, so verify they use the same
	* encryption policy. Compare the fscrypt_info structs if the keys are
	* available, otherwise retrieve and compare the fscrypt_contexts.
	*
	* Note that the fscrypt_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 fscrypt_context retrieval and keyring search.
	*
	* In any case, if an unexpected error occurs, fall back to "forbidden".
	*/

	res = fscrypt_get_encryption_info(parent);
	if (res)
	return 0;
	res = fscrypt_get_encryption_info(child);
	if (res)
	return 0;
	parent_ci = parent->i_crypt_info;
	child_ci = child->i_crypt_info;

	if (parent_ci && child_ci) {
	return memcmp(parent_ci->ci_master_key, child_ci->ci_master_key,
	FS_KEY_DESCRIPTOR_SIZE) == 0 &&
	(parent_ci->ci_data_mode == child_ci->ci_data_mode) &&
	(parent_ci->ci_filename_mode ==
	child_ci->ci_filename_mode) &&
	(parent_ci->ci_flags == child_ci->ci_flags);
	}

	res = cops->get_context(parent, &parent_ctx, sizeof(parent_ctx));
	if (res != sizeof(parent_ctx))
	return 0;

	res = cops->get_context(child, &child_ctx, sizeof(child_ctx));
	if (res != sizeof(child_ctx))
	return 0;

	return memcmp(parent_ctx.master_key_descriptor,
	child_ctx.master_key_descriptor,
	FS_KEY_DESCRIPTOR_SIZE) == 0 &&
	(parent_ctx.contents_encryption_mode ==
	child_ctx.contents_encryption_mode) &&
	(parent_ctx.filenames_encryption_mode ==
	child_ctx.filenames_encryption_mode) &&
	(parent_ctx.flags == child_ctx.flags);
	}
	EXPORT_SYMBOL(fscrypt_has_permitted_context);

	/**
	* fscrypt_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 i_crypt_info if true
	*
	* Return: 0 on success, -errno on failure
	*/
	int fscrypt_inherit_context(struct inode parent, struct inode child,
	void *fs_data, bool preload)
	{
	struct fscrypt_context ctx;
	struct fscrypt_info *ci;
	int res;

	res = fscrypt_get_encryption_info(parent);
	if (res < 0)
	return res;

	ci = parent->i_crypt_info;
	if (ci == NULL)
	return -ENOKEY;

	ctx.format = FS_ENCRYPTION_CONTEXT_FORMAT_V1;
	ctx.contents_encryption_mode = ci->ci_data_mode;
	ctx.filenames_encryption_mode = ci->ci_filename_mode;
	ctx.flags = ci->ci_flags;
	memcpy(ctx.master_key_descriptor, ci->ci_master_key,
	FS_KEY_DESCRIPTOR_SIZE);
	get_random_bytes(ctx.nonce, FS_KEY_DERIVATION_NONCE_SIZE);
	BUILD_BUG_ON(sizeof(ctx) != FSCRYPT_SET_CONTEXT_MAX_SIZE);
	res = parent->i_sb->s_cop->set_context(child, &ctx,
	sizeof(ctx), fs_data);
	if (res)
	return res;
	return preload ? fscrypt_get_encryption_info(child): 0;
	}
	EXPORT_SYMBOL(fscrypt_inherit_context);