![Theodore Ts'o](/assets/img/avatar_default.png)
This obscures the length of the filenames, to decrease the amount of information leakage. By default, we pad the filenames to the next 4 byte boundaries. This costs nothing, since the directory entries are aligned to 4 byte boundaries anyway. Filenames can also be padded to 8, 16, or 32 bytes, which will consume more directory space. Change-Id: Ibb7a0fb76d2c48e2061240a709358ff40b14f322 Signed-off-by: Theodore Ts'o <tytso@mit.edu>
199 lines
6 KiB
C
199 lines
6 KiB
C
/*
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* linux/fs/ext4/crypto_policy.c
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*
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* Copyright (C) 2015, Google, Inc.
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*
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* This contains encryption policy functions for ext4
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*
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* Written by Michael Halcrow, 2015.
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*/
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#include <linux/random.h>
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#include <linux/string.h>
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#include <linux/types.h>
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#include "ext4.h"
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#include "xattr.h"
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static int ext4_inode_has_encryption_context(struct inode *inode)
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{
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int res = ext4_xattr_get(inode, EXT4_XATTR_INDEX_ENCRYPTION,
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EXT4_XATTR_NAME_ENCRYPTION_CONTEXT, NULL, 0);
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return (res > 0);
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}
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/*
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* check whether the policy is consistent with the encryption context
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* for the inode
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*/
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static int ext4_is_encryption_context_consistent_with_policy(
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struct inode *inode, const struct ext4_encryption_policy *policy)
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{
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struct ext4_encryption_context ctx;
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int res = ext4_xattr_get(inode, EXT4_XATTR_INDEX_ENCRYPTION,
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EXT4_XATTR_NAME_ENCRYPTION_CONTEXT, &ctx,
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sizeof(ctx));
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if (res != sizeof(ctx))
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return 0;
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return (memcmp(ctx.master_key_descriptor, policy->master_key_descriptor,
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EXT4_KEY_DESCRIPTOR_SIZE) == 0 &&
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(ctx.flags ==
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policy->flags) &&
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(ctx.contents_encryption_mode ==
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policy->contents_encryption_mode) &&
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(ctx.filenames_encryption_mode ==
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policy->filenames_encryption_mode));
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}
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static int ext4_create_encryption_context_from_policy(
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struct inode *inode, const struct ext4_encryption_policy *policy)
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{
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struct ext4_encryption_context ctx;
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int res = 0;
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ctx.format = EXT4_ENCRYPTION_CONTEXT_FORMAT_V1;
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memcpy(ctx.master_key_descriptor, policy->master_key_descriptor,
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EXT4_KEY_DESCRIPTOR_SIZE);
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if (!ext4_valid_contents_enc_mode(policy->contents_encryption_mode)) {
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printk(KERN_WARNING
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"%s: Invalid contents encryption mode %d\n", __func__,
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policy->contents_encryption_mode);
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return -EINVAL;
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}
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if (!ext4_valid_filenames_enc_mode(policy->filenames_encryption_mode)) {
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printk(KERN_WARNING
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"%s: Invalid filenames encryption mode %d\n", __func__,
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policy->filenames_encryption_mode);
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return -EINVAL;
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}
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if (policy->flags & ~EXT4_POLICY_FLAGS_VALID)
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return -EINVAL;
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ctx.contents_encryption_mode = policy->contents_encryption_mode;
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ctx.filenames_encryption_mode = policy->filenames_encryption_mode;
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ctx.flags = policy->flags;
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BUILD_BUG_ON(sizeof(ctx.nonce) != EXT4_KEY_DERIVATION_NONCE_SIZE);
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get_random_bytes(ctx.nonce, EXT4_KEY_DERIVATION_NONCE_SIZE);
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res = ext4_xattr_set(inode, EXT4_XATTR_INDEX_ENCRYPTION,
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EXT4_XATTR_NAME_ENCRYPTION_CONTEXT, &ctx,
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sizeof(ctx), 0);
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if (!res)
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ext4_set_inode_flag(inode, EXT4_INODE_ENCRYPT);
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return res;
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}
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int ext4_process_policy(const struct ext4_encryption_policy *policy,
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struct inode *inode)
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{
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if (policy->version != 0)
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return -EINVAL;
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if (!ext4_inode_has_encryption_context(inode)) {
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if (!ext4_empty_dir(inode))
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return -ENOTEMPTY;
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return ext4_create_encryption_context_from_policy(inode,
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policy);
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}
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if (ext4_is_encryption_context_consistent_with_policy(inode, policy))
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return 0;
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printk(KERN_WARNING "%s: Policy inconsistent with encryption context\n",
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__func__);
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return -EINVAL;
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}
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int ext4_get_policy(struct inode *inode, struct ext4_encryption_policy *policy)
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{
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struct ext4_encryption_context ctx;
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int res = ext4_xattr_get(inode, EXT4_XATTR_INDEX_ENCRYPTION,
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EXT4_XATTR_NAME_ENCRYPTION_CONTEXT,
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&ctx, sizeof(ctx));
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if (res != sizeof(ctx))
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return -ENOENT;
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if (ctx.format != EXT4_ENCRYPTION_CONTEXT_FORMAT_V1)
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return -EINVAL;
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policy->version = 0;
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policy->contents_encryption_mode = ctx.contents_encryption_mode;
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policy->filenames_encryption_mode = ctx.filenames_encryption_mode;
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policy->flags = ctx.flags;
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memcpy(&policy->master_key_descriptor, ctx.master_key_descriptor,
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EXT4_KEY_DESCRIPTOR_SIZE);
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return 0;
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}
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int ext4_is_child_context_consistent_with_parent(struct inode *parent,
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struct inode *child)
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{
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struct ext4_encryption_context parent_ctx, child_ctx;
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int res;
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if ((parent == NULL) || (child == NULL)) {
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pr_err("parent %p child %p\n", parent, child);
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BUG_ON(1);
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}
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/* no restrictions if the parent directory is not encrypted */
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if (!ext4_encrypted_inode(parent))
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return 1;
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res = ext4_xattr_get(parent, EXT4_XATTR_INDEX_ENCRYPTION,
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EXT4_XATTR_NAME_ENCRYPTION_CONTEXT,
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&parent_ctx, sizeof(parent_ctx));
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if (res != sizeof(parent_ctx))
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return 0;
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/* if the child directory is not encrypted, this is always a problem */
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if (!ext4_encrypted_inode(child))
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return 0;
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res = ext4_xattr_get(child, EXT4_XATTR_INDEX_ENCRYPTION,
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EXT4_XATTR_NAME_ENCRYPTION_CONTEXT,
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&child_ctx, sizeof(child_ctx));
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if (res != sizeof(child_ctx))
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return 0;
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return (memcmp(parent_ctx.master_key_descriptor,
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child_ctx.master_key_descriptor,
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EXT4_KEY_DESCRIPTOR_SIZE) == 0 &&
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(parent_ctx.contents_encryption_mode ==
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child_ctx.contents_encryption_mode) &&
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(parent_ctx.filenames_encryption_mode ==
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child_ctx.filenames_encryption_mode));
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}
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/**
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* ext4_inherit_context() - Sets a child context from its parent
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* @parent: Parent inode from which the context is inherited.
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* @child: Child inode that inherits the context from @parent.
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*
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* Return: Zero on success, non-zero otherwise
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*/
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int ext4_inherit_context(struct inode *parent, struct inode *child)
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{
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struct ext4_encryption_context ctx;
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int res = ext4_xattr_get(parent, EXT4_XATTR_INDEX_ENCRYPTION,
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EXT4_XATTR_NAME_ENCRYPTION_CONTEXT,
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&ctx, sizeof(ctx));
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if (res != sizeof(ctx)) {
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if (DUMMY_ENCRYPTION_ENABLED(EXT4_SB(parent->i_sb))) {
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ctx.format = EXT4_ENCRYPTION_CONTEXT_FORMAT_V1;
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ctx.contents_encryption_mode =
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EXT4_ENCRYPTION_MODE_AES_256_XTS;
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ctx.filenames_encryption_mode =
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EXT4_ENCRYPTION_MODE_AES_256_CTS;
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ctx.flags = 0;
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memset(ctx.master_key_descriptor, 0x42,
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EXT4_KEY_DESCRIPTOR_SIZE);
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res = 0;
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} else {
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goto out;
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}
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}
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get_random_bytes(ctx.nonce, EXT4_KEY_DERIVATION_NONCE_SIZE);
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res = ext4_xattr_set(child, EXT4_XATTR_INDEX_ENCRYPTION,
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EXT4_XATTR_NAME_ENCRYPTION_CONTEXT, &ctx,
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sizeof(ctx), 0);
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out:
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if (!res)
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ext4_set_inode_flag(child, EXT4_INODE_ENCRYPT);
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return res;
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}
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