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>

5 files changed, 317 insertions, 0 deletions

diff --git a/fs/ext4/Makefile b/fs/ext4/Makefile
index cd6f50fce278..3886ee45f556 100644
--- a/fs/ext4/Makefile
+++ b/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
diff --git a/fs/ext4/crypto_policy.c b/fs/ext4/crypto_policy.c
new file mode 100644
index 000000000000..532b69c0afab
--- /dev/null
+++ b/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;
+}
diff --git a/fs/ext4/ext4.h b/fs/ext4/ext4.h
index 180111de2302..ab873aa9955e 100644
--- a/fs/ext4/ext4.h
+++ b/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 *,
diff --git a/fs/ext4/ext4_crypto.h b/fs/ext4/ext4_crypto.h
new file mode 100644
index 000000000000..a69d2ba54bee
--- /dev/null
+++ b/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 */
diff --git a/fs/ext4/ioctl.c b/fs/ext4/ioctl.c
index f1aa32c2277c..2cb9e178d1c5 100644
--- a/fs/ext4/ioctl.c
+++ b/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;