ext4 crypto: add encryption policy and password salt support

Signed-off-by: Michael Halcrow <mhalcrow@google.com>
Signed-off-by: Theodore Ts'o <tytso@mit.edu>
Signed-off-by: Ildar Muslukhov <muslukhovi@gmail.com>

fs/ext4/Makefile

@@ -12,3 +12,4 @@ ext4-y	:= balloc.o bitmap.o dir.o file.o fsync.o ialloc.o inode.o page-io.o \
 
 ext4-$(CONFIG_EXT4_FS_POSIX_ACL)	+= acl.o
 ext4-$(CONFIG_EXT4_FS_SECURITY)		+= xattr_security.o
+ext4-$(CONFIG_EXT4_FS_ENCRYPTION)	+= crypto_policy.o

fs/ext4/crypto_policy.c

@@ -0,0 +1,167 @@
+/*
+ * linux/fs/ext4/crypto_policy.c
+ *
+ * Copyright (C) 2015, Google, Inc.
+ *
+ * This contains encryption policy functions for ext4
+ *
+ * Written by Michael Halcrow, 2015.
+ */
+
+#include <linux/random.h>
+#include <linux/string.h>
+#include <linux/types.h>
+
+#include "ext4.h"
+#include "xattr.h"
+
+static int ext4_inode_has_encryption_context(struct inode *inode)
+{
+	int res = ext4_xattr_get(inode, EXT4_XATTR_INDEX_ENCRYPTION,
+				 EXT4_XATTR_NAME_ENCRYPTION_CONTEXT, NULL, 0);
+	return (res > 0);
+}
+
+/*
+ * check whether the policy is consistent with the encryption context
+ * for the inode
+ */
+static int ext4_is_encryption_context_consistent_with_policy(
+	struct inode *inode, const struct ext4_encryption_policy *policy)
+{
+	struct ext4_encryption_context ctx;
+	int res = ext4_xattr_get(inode, EXT4_XATTR_INDEX_ENCRYPTION,
+				 EXT4_XATTR_NAME_ENCRYPTION_CONTEXT, &ctx,
+				 sizeof(ctx));
+	if (res != sizeof(ctx))
+		return 0;
+	return (memcmp(ctx.master_key_descriptor, policy->master_key_descriptor,
+			EXT4_KEY_DESCRIPTOR_SIZE) == 0 &&
+		(ctx.contents_encryption_mode ==
+		 policy->contents_encryption_mode) &&
+		(ctx.filenames_encryption_mode ==
+		 policy->filenames_encryption_mode));
+}
+
+static int ext4_create_encryption_context_from_policy(
+	struct inode *inode, const struct ext4_encryption_policy *policy)
+{
+	struct ext4_encryption_context ctx;
+	int res = 0;
+
+	ctx.format = EXT4_ENCRYPTION_CONTEXT_FORMAT_V1;
+	memcpy(ctx.master_key_descriptor, policy->master_key_descriptor,
+	       EXT4_KEY_DESCRIPTOR_SIZE);
+	ctx.contents_encryption_mode = policy->contents_encryption_mode;
+	ctx.filenames_encryption_mode = policy->filenames_encryption_mode;
+	BUILD_BUG_ON(sizeof(ctx.nonce) != EXT4_KEY_DERIVATION_NONCE_SIZE);
+	get_random_bytes(ctx.nonce, EXT4_KEY_DERIVATION_NONCE_SIZE);
+
+	res = ext4_xattr_set(inode, EXT4_XATTR_INDEX_ENCRYPTION,
+			     EXT4_XATTR_NAME_ENCRYPTION_CONTEXT, &ctx,
+			     sizeof(ctx), 0);
+	if (!res)
+		ext4_set_inode_flag(inode, EXT4_INODE_ENCRYPT);
+	return res;
+}
+
+int ext4_process_policy(const struct ext4_encryption_policy *policy,
+			struct inode *inode)
+{
+	if (policy->version != 0)
+		return -EINVAL;
+
+	if (!ext4_inode_has_encryption_context(inode)) {
+		if (!ext4_empty_dir(inode))
+			return -ENOTEMPTY;
+		return ext4_create_encryption_context_from_policy(inode,
+								  policy);
+	}
+
+	if (ext4_is_encryption_context_consistent_with_policy(inode, policy))
+		return 0;
+
+	printk(KERN_WARNING "%s: Policy inconsistent with encryption context\n",
+	       __func__);
+	return -EINVAL;
+}
+
+int ext4_get_policy(struct inode *inode, struct ext4_encryption_policy *policy)
+{
+	struct ext4_encryption_context ctx;
+
+	int res = ext4_xattr_get(inode, EXT4_XATTR_INDEX_ENCRYPTION,
+				 EXT4_XATTR_NAME_ENCRYPTION_CONTEXT,
+				 &ctx, sizeof(ctx));
+	if (res != sizeof(ctx))
+		return -ENOENT;
+	if (ctx.format != EXT4_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;
+	memcpy(&policy->master_key_descriptor, ctx.master_key_descriptor,
+	       EXT4_KEY_DESCRIPTOR_SIZE);
+	return 0;
+}
+
+int ext4_is_child_context_consistent_with_parent(struct inode *parent,
+						 struct inode *child)
+{
+	struct ext4_encryption_context parent_ctx, child_ctx;
+	int res;
+
+	if ((parent == NULL) || (child == NULL)) {
+		pr_err("parent %p child %p\n", parent, child);
+		BUG_ON(1);
+	}
+	/* no restrictions if the parent directory is not encrypted */
+	if (!ext4_encrypted_inode(parent))
+		return 1;
+	res = ext4_xattr_get(parent, EXT4_XATTR_INDEX_ENCRYPTION,
+			     EXT4_XATTR_NAME_ENCRYPTION_CONTEXT,
+			     &parent_ctx, sizeof(parent_ctx));
+	if (res != sizeof(parent_ctx))
+		return 0;
+	/* if the child directory is not encrypted, this is always a problem */
+	if (!ext4_encrypted_inode(child))
+		return 0;
+	res = ext4_xattr_get(child, EXT4_XATTR_INDEX_ENCRYPTION,
+			     EXT4_XATTR_NAME_ENCRYPTION_CONTEXT,
+			     &child_ctx, sizeof(child_ctx));
+	if (res != sizeof(child_ctx))
+		return 0;
+	return (memcmp(parent_ctx.master_key_descriptor,
+		       child_ctx.master_key_descriptor,
+		       EXT4_KEY_DESCRIPTOR_SIZE) == 0 &&
+		(parent_ctx.contents_encryption_mode ==
+		 child_ctx.contents_encryption_mode) &&
+		(parent_ctx.filenames_encryption_mode ==
+		 child_ctx.filenames_encryption_mode));
+}
+
+/**
+ * ext4_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.
+ *
+ * Return: Zero on success, non-zero otherwise
+ */
+int ext4_inherit_context(struct inode *parent, struct inode *child)
+{
+	struct ext4_encryption_context ctx;
+	int res = ext4_xattr_get(parent, EXT4_XATTR_INDEX_ENCRYPTION,
+				 EXT4_XATTR_NAME_ENCRYPTION_CONTEXT,
+				 &ctx, sizeof(ctx));
+
+	if (res != sizeof(ctx))
+		return -ENOENT;
+
+	get_random_bytes(ctx.nonce, EXT4_KEY_DERIVATION_NONCE_SIZE);
+	res = ext4_xattr_set(child, EXT4_XATTR_INDEX_ENCRYPTION,
+			     EXT4_XATTR_NAME_ENCRYPTION_CONTEXT, &ctx,
+			     sizeof(ctx), 0);
+	if (!res)
+		ext4_set_inode_flag(child, EXT4_INODE_ENCRYPT);
+	return res;
+}

fs/ext4/ext4.h

@@ -589,6 +589,8 @@ enum {
 #define EXT4_ENCRYPTION_MODE_AES_256_CBC	3
 #define EXT4_ENCRYPTION_MODE_AES_256_CTS	4
 
+#include "ext4_crypto.h"
+
 /*
  * ioctl commands
  */
@@ -610,6 +612,9 @@ enum {
 #define EXT4_IOC_RESIZE_FS		_IOW('f', 16, __u64)
 #define EXT4_IOC_SWAP_BOOT		_IO('f', 17)
 #define EXT4_IOC_PRECACHE_EXTENTS	_IO('f', 18)
+#define EXT4_IOC_SET_ENCRYPTION_POLICY	_IOR('f', 19, struct ext4_encryption_policy)
+#define EXT4_IOC_GET_ENCRYPTION_PWSALT	_IOW('f', 20, __u8[16])
+#define EXT4_IOC_GET_ENCRYPTION_POLICY	_IOW('f', 21, struct ext4_encryption_policy)
 
 #if defined(__KERNEL__) && defined(CONFIG_COMPAT)
 /*
@@ -2011,6 +2016,16 @@ extern unsigned ext4_free_clusters_after_init(struct super_block *sb,
 					      struct ext4_group_desc *gdp);
 ext4_fsblk_t ext4_inode_to_goal_block(struct inode *);
 
+/* crypto_policy.c */
+int ext4_is_child_context_consistent_with_parent(struct inode *parent,
+						 struct inode *child);
+int ext4_inherit_context(struct inode *parent, struct inode *child);
+void ext4_to_hex(char *dst, char *src, size_t src_size);
+int ext4_process_policy(const struct ext4_encryption_policy *policy,
+			struct inode *inode);
+int ext4_get_policy(struct inode *inode,
+		    struct ext4_encryption_policy *policy);
+
 /* dir.c */
 extern int __ext4_check_dir_entry(const char *, unsigned int, struct inode *,
 				  struct file *,

fs/ext4/ext4_crypto.h

@@ -0,0 +1,49 @@
+/*
+ * linux/fs/ext4/ext4_crypto.h
+ *
+ * Copyright (C) 2015, Google, Inc.
+ *
+ * This contains encryption header content for ext4
+ *
+ * Written by Michael Halcrow, 2015.
+ */
+
+#ifndef _EXT4_CRYPTO_H
+#define _EXT4_CRYPTO_H
+
+#include <linux/fs.h>
+
+#define EXT4_KEY_DESCRIPTOR_SIZE 8
+
+/* Policy provided via an ioctl on the topmost directory */
+struct ext4_encryption_policy {
+	char version;
+	char contents_encryption_mode;
+	char filenames_encryption_mode;
+	char master_key_descriptor[EXT4_KEY_DESCRIPTOR_SIZE];
+} __attribute__((__packed__));
+
+#define EXT4_ENCRYPTION_CONTEXT_FORMAT_V1 1
+#define EXT4_KEY_DERIVATION_NONCE_SIZE 16
+
+/**
+ * Encryption context for inode
+ *
+ * Protector format:
+ *  1 byte: Protector format (1 = this version)
+ *  1 byte: File contents encryption mode
+ *  1 byte: File names encryption mode
+ *  1 byte: Reserved
+ *  8 bytes: Master Key descriptor
+ *  16 bytes: Encryption Key derivation nonce
+ */
+struct ext4_encryption_context {
+	char format;
+	char contents_encryption_mode;
+	char filenames_encryption_mode;
+	char reserved;
+	char master_key_descriptor[EXT4_KEY_DESCRIPTOR_SIZE];
+	char nonce[EXT4_KEY_DERIVATION_NONCE_SIZE];
+} __attribute__((__packed__));
+
+#endif	/* _EXT4_CRYPTO_H */

fs/ext4/ioctl.c

@@ -13,6 +13,7 @@
 #include <linux/compat.h>
 #include <linux/mount.h>
 #include <linux/file.h>
+#include <linux/random.h>
 #include <asm/uaccess.h>
 #include "ext4_jbd2.h"
 #include "ext4.h"
@@ -195,6 +196,16 @@ journal_err_out:
 	return err;
 }
 
+static int uuid_is_zero(__u8 u[16])
+{
+	int	i;
+
+	for (i = 0; i < 16; i++)
+		if (u[i])
+			return 0;
+	return 1;
+}
+
 long ext4_ioctl(struct file *filp, unsigned int cmd, unsigned long arg)
 {
 	struct inode *inode = file_inode(filp);
@@ -614,7 +625,78 @@ resizefs_out:
 	}
 	case EXT4_IOC_PRECACHE_EXTENTS:
 		return ext4_ext_precache(inode);
+	case EXT4_IOC_SET_ENCRYPTION_POLICY: {
+#ifdef CONFIG_EXT4_FS_ENCRYPTION
+		struct ext4_encryption_policy policy;
+		int err = 0;
 
+		if (copy_from_user(&policy,
+				   (struct ext4_encryption_policy __user *)arg,
+				   sizeof(policy))) {
+			err = -EFAULT;
+			goto encryption_policy_out;
+		}
+
+		err = ext4_process_policy(&policy, inode);
+encryption_policy_out:
+		return err;
+#else
+		return -EOPNOTSUPP;
+#endif
+	}
+	case EXT4_IOC_GET_ENCRYPTION_PWSALT: {
+		int err, err2;
+		struct ext4_sb_info *sbi = EXT4_SB(sb);
+		handle_t *handle;
+
+		if (!ext4_sb_has_crypto(sb))
+			return -EOPNOTSUPP;
+		if (uuid_is_zero(sbi->s_es->s_encrypt_pw_salt)) {
+			err = mnt_want_write_file(filp);
+			if (err)
+				return err;
+			handle = ext4_journal_start_sb(sb, EXT4_HT_MISC, 1);
+			if (IS_ERR(handle)) {
+				err = PTR_ERR(handle);
+				goto pwsalt_err_exit;
+			}
+			err = ext4_journal_get_write_access(handle, sbi->s_sbh);
+			if (err)
+				goto pwsalt_err_journal;
+			generate_random_uuid(sbi->s_es->s_encrypt_pw_salt);
+			err = ext4_handle_dirty_metadata(handle, NULL,
+							 sbi->s_sbh);
+		pwsalt_err_journal:
+			err2 = ext4_journal_stop(handle);
+			if (err2 && !err)
+				err = err2;
+		pwsalt_err_exit:
+			mnt_drop_write_file(filp);
+			if (err)
+				return err;
+		}
+		if (copy_to_user((void *) arg, sbi->s_es->s_encrypt_pw_salt,
+				 16))
+			return -EFAULT;
+		return 0;
+	}
+	case EXT4_IOC_GET_ENCRYPTION_POLICY: {
+#ifdef CONFIG_EXT4_FS_ENCRYPTION
+		struct ext4_encryption_policy policy;
+		int err = 0;
+
+		if (!ext4_encrypted_inode(inode))
+			return -ENOENT;
+		err = ext4_get_policy(inode, &policy);
+		if (err)
+			return err;
+		if (copy_to_user((void *)arg, &policy, sizeof(policy)))
+			return -EFAULT;
+		return 0;
+#else
+		return -EOPNOTSUPP;
+#endif
+	}
 	default:
 		return -ENOTTY;
 	}
@@ -679,6 +761,9 @@ long ext4_compat_ioctl(struct file *file, unsigned int cmd, unsigned long arg)
 	case FITRIM:
 	case EXT4_IOC_RESIZE_FS:
 	case EXT4_IOC_PRECACHE_EXTENTS:
+	case EXT4_IOC_SET_ENCRYPTION_POLICY:
+	case EXT4_IOC_GET_ENCRYPTION_PWSALT:
+	case EXT4_IOC_GET_ENCRYPTION_POLICY:
 		break;
 	default:
 		return -ENOIOCTLCMD;