ext4 crypto: add encryption key management facilities

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

4 files changed, 179 insertions, 1 deletions

diff --git a/fs/ext4/Makefile b/fs/ext4/Makefile
index 1b1c5619523d..4e5af21f1050 100644
--- a/fs/ext4/Makefile
+++ b/fs/ext4/Makefile
@@ -12,4 +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-$(CONFIG_EXT4_FS_ENCRYPTION)       += crypto_policy.o crypto.o
+ext4-$(CONFIG_EXT4_FS_ENCRYPTION)       += crypto_policy.o crypto.o crypto_key.o
diff --git a/fs/ext4/crypto_key.c b/fs/ext4/crypto_key.c
new file mode 100644
index 000000000000..572bd97f58dd
--- /dev/null
+++ b/fs/ext4/crypto_key.c
@@ -0,0 +1,162 @@
+/*
+ * linux/fs/ext4/crypto_key.c
+ *
+ * Copyright (C) 2015, Google, Inc.
+ *
+ * This contains encryption key functions for ext4
+ *
+ * Written by Michael Halcrow, Ildar Muslukhov, and Uday Savagaonkar, 2015.
+ */
+
+#include <keys/encrypted-type.h>
+#include <keys/user-type.h>
+#include <linux/random.h>
+#include <linux/scatterlist.h>
+#include <uapi/linux/keyctl.h>
+
+#include "ext4.h"
+#include "xattr.h"
+
+static void derive_crypt_complete(struct crypto_async_request *req, int rc)
+{
+        struct ext4_completion_result *ecr = req->data;
+
+        if (rc == -EINPROGRESS)
+                return;
+
+        ecr->res = rc;
+        complete(&ecr->completion);
+}
+
+/**
+ * ext4_derive_key_aes() - Derive a key using AES-128-ECB
+ * @deriving_key: Encryption key used for derivatio.
+ * @source_key:   Source key to which to apply derivation.
+ * @derived_key:  Derived key.
+ *
+ * Return: Zero on success; non-zero otherwise.
+ */
+static int ext4_derive_key_aes(char deriving_key[EXT4_AES_128_ECB_KEY_SIZE],
+                               char source_key[EXT4_AES_256_XTS_KEY_SIZE],
+                               char derived_key[EXT4_AES_256_XTS_KEY_SIZE])
+{
+        int res = 0;
+        struct ablkcipher_request *req = NULL;
+        DECLARE_EXT4_COMPLETION_RESULT(ecr);
+        struct scatterlist src_sg, dst_sg;
+        struct crypto_ablkcipher *tfm = crypto_alloc_ablkcipher("ecb(aes)", 0,
+                                                                0);
+
+        if (IS_ERR(tfm)) {
+                res = PTR_ERR(tfm);
+                tfm = NULL;
+                goto out;
+        }
+        crypto_ablkcipher_set_flags(tfm, CRYPTO_TFM_REQ_WEAK_KEY);
+        req = ablkcipher_request_alloc(tfm, GFP_NOFS);
+        if (!req) {
+                res = -ENOMEM;
+                goto out;
+        }
+        ablkcipher_request_set_callback(req,
+                        CRYPTO_TFM_REQ_MAY_BACKLOG | CRYPTO_TFM_REQ_MAY_SLEEP,
+                        derive_crypt_complete, &ecr);
+        res = crypto_ablkcipher_setkey(tfm, deriving_key,
+                                       EXT4_AES_128_ECB_KEY_SIZE);
+        if (res < 0)
+                goto out;
+        sg_init_one(&src_sg, source_key, EXT4_AES_256_XTS_KEY_SIZE);
+        sg_init_one(&dst_sg, derived_key, EXT4_AES_256_XTS_KEY_SIZE);
+        ablkcipher_request_set_crypt(req, &src_sg, &dst_sg,
+                                     EXT4_AES_256_XTS_KEY_SIZE, NULL);
+        res = crypto_ablkcipher_encrypt(req);
+        if (res == -EINPROGRESS || res == -EBUSY) {
+                BUG_ON(req->base.data != &ecr);
+                wait_for_completion(&ecr.completion);
+                res = ecr.res;
+        }
+
+out:
+        if (req)
+                ablkcipher_request_free(req);
+        if (tfm)
+                crypto_free_ablkcipher(tfm);
+        return res;
+}
+
+/**
+ * ext4_generate_encryption_key() - generates an encryption key
+ * @inode: The inode to generate the encryption key for.
+ */
+int ext4_generate_encryption_key(struct inode *inode)
+{
+        struct ext4_inode_info *ei = EXT4_I(inode);
+        struct ext4_encryption_key *crypt_key = &ei->i_encryption_key;
+        char full_key_descriptor[EXT4_KEY_DESC_PREFIX_SIZE +
+                                 (EXT4_KEY_DESCRIPTOR_SIZE * 2) + 1];
+        struct key *keyring_key = NULL;
+        struct ext4_encryption_key *master_key;
+        struct ext4_encryption_context ctx;
+        struct user_key_payload *ukp;
+        int res = ext4_xattr_get(inode, EXT4_XATTR_INDEX_ENCRYPTION,
+                                 EXT4_XATTR_NAME_ENCRYPTION_CONTEXT,
+                                 &ctx, sizeof(ctx));
+
+        if (res != sizeof(ctx)) {
+                if (res > 0)
+                        res = -EINVAL;
+                goto out;
+        }
+        res = 0;
+
+        memcpy(full_key_descriptor, EXT4_KEY_DESC_PREFIX,
+               EXT4_KEY_DESC_PREFIX_SIZE);
+        sprintf(full_key_descriptor + EXT4_KEY_DESC_PREFIX_SIZE,
+                "%*phN", EXT4_KEY_DESCRIPTOR_SIZE,
+                ctx.master_key_descriptor);
+        full_key_descriptor[EXT4_KEY_DESC_PREFIX_SIZE +
+                            (2 * EXT4_KEY_DESCRIPTOR_SIZE)] = '\0';
+        keyring_key = request_key(&key_type_logon, full_key_descriptor, NULL);
+        if (IS_ERR(keyring_key)) {
+                res = PTR_ERR(keyring_key);
+                keyring_key = NULL;
+                goto out;
+        }
+        BUG_ON(keyring_key->type != &key_type_logon);
+        ukp = ((struct user_key_payload *)keyring_key->payload.data);
+        if (ukp->datalen != sizeof(struct ext4_encryption_key)) {
+                res = -EINVAL;
+                goto out;
+        }
+        master_key = (struct ext4_encryption_key *)ukp->data;
+
+        if (S_ISREG(inode->i_mode))
+                crypt_key->mode = ctx.contents_encryption_mode;
+        else if (S_ISDIR(inode->i_mode) || S_ISLNK(inode->i_mode))
+                crypt_key->mode = ctx.filenames_encryption_mode;
+        else {
+                printk(KERN_ERR "ext4 crypto: Unsupported inode type.\n");
+                BUG();
+        }
+        crypt_key->size = ext4_encryption_key_size(crypt_key->mode);
+        BUG_ON(!crypt_key->size);
+        BUILD_BUG_ON(EXT4_AES_128_ECB_KEY_SIZE !=
+                     EXT4_KEY_DERIVATION_NONCE_SIZE);
+        BUG_ON(master_key->size != EXT4_AES_256_XTS_KEY_SIZE);
+        BUG_ON(crypt_key->size < EXT4_AES_256_CBC_KEY_SIZE);
+        res = ext4_derive_key_aes(ctx.nonce, master_key->raw, crypt_key->raw);
+out:
+        if (keyring_key)
+                key_put(keyring_key);
+        if (res < 0)
+                crypt_key->mode = EXT4_ENCRYPTION_MODE_INVALID;
+        return res;
+}
+
+int ext4_has_encryption_key(struct inode *inode)
+{
+        struct ext4_inode_info *ei = EXT4_I(inode);
+        struct ext4_encryption_key *crypt_key = &ei->i_encryption_key;
+
+        return (crypt_key->mode != EXT4_ENCRYPTION_MODE_INVALID);
+}
diff --git a/fs/ext4/ext4.h b/fs/ext4/ext4.h
index 71619ef72225..99a2d67f65b7 100644
--- a/fs/ext4/ext4.h
+++ b/fs/ext4/ext4.h
@@ -2078,6 +2078,19 @@ static inline int ext4_sb_has_crypto(struct super_block *sb)
 }
 #endif
 
+/* crypto_key.c */
+int ext4_generate_encryption_key(struct inode *inode);
+
+#ifdef CONFIG_EXT4_FS_ENCRYPTION
+int ext4_has_encryption_key(struct inode *inode);
+#else
+static inline int ext4_has_encryption_key(struct inode *inode)
+{
+        return 0;
+}
+#endif
+
+
 /* 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
index 9d5d2e56cc46..6a7c0c06b2be 100644
--- a/fs/ext4/ext4_crypto.h
+++ b/fs/ext4/ext4_crypto.h
@@ -55,6 +55,9 @@ struct ext4_encryption_context {
 #define EXT4_AES_256_XTS_KEY_SIZE 64
 #define EXT4_MAX_KEY_SIZE 64
 
+#define EXT4_KEY_DESC_PREFIX "ext4:"
+#define EXT4_KEY_DESC_PREFIX_SIZE 5
+
 struct ext4_encryption_key {
         uint32_t mode;
         char raw[EXT4_MAX_KEY_SIZE];