encrypted-keys: add ecryptfs format support

The 'encrypted' key type defines its own payload format which contains a
symmetric key randomly generated that cannot be used directly to mount
an eCryptfs filesystem, because it expects an authentication token
structure.

This patch introduces the new format 'ecryptfs' that allows to store an
authentication token structure inside the encrypted key payload containing
a randomly generated symmetric key, as the same for the format 'default'.

More details about the usage of encrypted keys with the eCryptfs
filesystem can be found in the file 'Documentation/keys-ecryptfs.txt'.

Signed-off-by: Roberto Sassu <roberto.sassu@polito.it>
Acked-by: Gianluca Ramunno <ramunno@polito.it>
Acked-by: Tyler Hicks <tyhicks@linux.vnet.ibm.com>
Signed-off-by: Mimi Zohar <zohar@linux.vnet.ibm.com>

4 files changed, 180 insertions, 8 deletions

diff --git a/security/keys/Makefile b/security/keys/Makefile
index 1bf090a..b34cc6e 100644
--- a/security/keys/Makefile
+++ b/security/keys/Makefile
@@ -14,7 +14,7 @@ obj-y := \
 	user_defined.o
 
 obj-$(CONFIG_TRUSTED_KEYS) += trusted.o
-obj-$(CONFIG_ENCRYPTED_KEYS) += encrypted.o
+obj-$(CONFIG_ENCRYPTED_KEYS) += ecryptfs_format.o encrypted.o
 obj-$(CONFIG_KEYS_COMPAT) += compat.o
 obj-$(CONFIG_PROC_FS) += proc.o
 obj-$(CONFIG_SYSCTL) += sysctl.o
diff --git a/security/keys/ecryptfs_format.c b/security/keys/ecryptfs_format.c
new file mode 100644
index 0000000..6daa3b6
--- /dev/null
+++ b/security/keys/ecryptfs_format.c
@@ -0,0 +1,81 @@
+/*
+ * ecryptfs_format.c: helper functions for the encrypted key type
+ *
+ * Copyright (C) 2006 International Business Machines Corp.
+ * Copyright (C) 2010 Politecnico di Torino, Italy
+ *                    TORSEC group -- http://security.polito.it
+ *
+ * Authors:
+ * Michael A. Halcrow <mahalcro@us.ibm.com>
+ * Tyler Hicks <tyhicks@ou.edu>
+ * Roberto Sassu <roberto.sassu@polito.it>
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, version 2 of the License.
+ */
+
+#include <linux/module.h>
+#include "ecryptfs_format.h"
+
+u8 *ecryptfs_get_auth_tok_key(struct ecryptfs_auth_tok *auth_tok)
+{
+	return auth_tok->token.password.session_key_encryption_key;
+}
+EXPORT_SYMBOL(ecryptfs_get_auth_tok_key);
+
+/*
+ * ecryptfs_get_versions()
+ *
+ * Source code taken from the software 'ecryptfs-utils' version 83.
+ *
+ */
+void ecryptfs_get_versions(int *major, int *minor, int *file_version)
+{
+	*major = ECRYPTFS_VERSION_MAJOR;
+	*minor = ECRYPTFS_VERSION_MINOR;
+	if (file_version)
+		*file_version = ECRYPTFS_SUPPORTED_FILE_VERSION;
+}
+EXPORT_SYMBOL(ecryptfs_get_versions);
+
+/*
+ * ecryptfs_fill_auth_tok - fill the ecryptfs_auth_tok structure
+ *
+ * Fill the ecryptfs_auth_tok structure with required ecryptfs data.
+ * The source code is inspired to the original function generate_payload()
+ * shipped with the software 'ecryptfs-utils' version 83.
+ *
+ */
+int ecryptfs_fill_auth_tok(struct ecryptfs_auth_tok *auth_tok,
+			   const char *key_desc)
+{
+	int major, minor;
+
+	ecryptfs_get_versions(&major, &minor, NULL);
+	auth_tok->version = (((uint16_t)(major << 8) & 0xFF00)
+			     | ((uint16_t)minor & 0x00FF));
+	auth_tok->token_type = ECRYPTFS_PASSWORD;
+	strncpy((char *)auth_tok->token.password.signature, key_desc,
+		ECRYPTFS_PASSWORD_SIG_SIZE);
+	auth_tok->token.password.session_key_encryption_key_bytes =
+		ECRYPTFS_MAX_KEY_BYTES;
+	/*
+	 * Removed auth_tok->token.password.salt and
+	 * auth_tok->token.password.session_key_encryption_key
+	 * initialization from the original code
+	 */
+	/* TODO: Make the hash parameterizable via policy */
+	auth_tok->token.password.flags |=
+		ECRYPTFS_SESSION_KEY_ENCRYPTION_KEY_SET;
+	/* The kernel code will encrypt the session key. */
+	auth_tok->session_key.encrypted_key[0] = 0;
+	auth_tok->session_key.encrypted_key_size = 0;
+	/* Default; subject to change by kernel eCryptfs */
+	auth_tok->token.password.hash_algo = PGP_DIGEST_ALGO_SHA512;
+	auth_tok->token.password.flags &= ~(ECRYPTFS_PERSISTENT_PASSWORD);
+	return 0;
+}
+EXPORT_SYMBOL(ecryptfs_fill_auth_tok);
+
+MODULE_LICENSE("GPL");
diff --git a/security/keys/ecryptfs_format.h b/security/keys/ecryptfs_format.h
new file mode 100644
index 0000000..40294de
--- /dev/null
+++ b/security/keys/ecryptfs_format.h
@@ -0,0 +1,30 @@
+/*
+ * ecryptfs_format.h: helper functions for the encrypted key type
+ *
+ * Copyright (C) 2006 International Business Machines Corp.
+ * Copyright (C) 2010 Politecnico di Torino, Italy
+ *                    TORSEC group -- http://security.polito.it
+ *
+ * Authors:
+ * Michael A. Halcrow <mahalcro@us.ibm.com>
+ * Tyler Hicks <tyhicks@ou.edu>
+ * Roberto Sassu <roberto.sassu@polito.it>
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, version 2 of the License.
+ */
+
+#ifndef __KEYS_ECRYPTFS_H
+#define __KEYS_ECRYPTFS_H
+
+#include <linux/ecryptfs.h>
+
+#define PGP_DIGEST_ALGO_SHA512   10
+
+u8 *ecryptfs_get_auth_tok_key(struct ecryptfs_auth_tok *auth_tok);
+void ecryptfs_get_versions(int *major, int *minor, int *file_version);
+int ecryptfs_fill_auth_tok(struct ecryptfs_auth_tok *auth_tok,
+			   const char *key_desc);
+
+#endif /* __KEYS_ECRYPTFS_H */
diff --git a/security/keys/encrypted.c b/security/keys/encrypted.c
index 89981c9..e7eca9e 100644
--- a/security/keys/encrypted.c
+++ b/security/keys/encrypted.c
@@ -29,11 +29,13 @@
 #include <linux/rcupdate.h>
 #include <linux/scatterlist.h>
 #include <linux/crypto.h>
+#include <linux/ctype.h>
 #include <crypto/hash.h>
 #include <crypto/sha.h>
 #include <crypto/aes.h>
 
 #include "encrypted.h"
+#include "ecryptfs_format.h"
 
 static const char KEY_TRUSTED_PREFIX[] = "trusted:";
 static const char KEY_USER_PREFIX[] = "user:";
@@ -41,11 +43,13 @@ static const char hash_alg[] = "sha256";
 static const char hmac_alg[] = "hmac(sha256)";
 static const char blkcipher_alg[] = "cbc(aes)";
 static const char key_format_default[] = "default";
+static const char key_format_ecryptfs[] = "ecryptfs";
 static unsigned int ivsize;
 static int blksize;
 
 #define KEY_TRUSTED_PREFIX_LEN (sizeof (KEY_TRUSTED_PREFIX) - 1)
 #define KEY_USER_PREFIX_LEN (sizeof (KEY_USER_PREFIX) - 1)
+#define KEY_ECRYPTFS_DESC_LEN 16
 #define HASH_SIZE SHA256_DIGEST_SIZE
 #define MAX_DATA_SIZE 4096
 #define MIN_DATA_SIZE  20
@@ -63,11 +67,12 @@ enum {
 };
 
 enum {
-	Opt_error = -1, Opt_default
+	Opt_error = -1, Opt_default, Opt_ecryptfs
 };
 
 static const match_table_t key_format_tokens = {
 	{Opt_default, "default"},
+	{Opt_ecryptfs, "ecryptfs"},
 	{Opt_error, NULL}
 };
 
@@ -95,6 +100,34 @@ static int aes_get_sizes(void)
 }
 
 /*
+ * valid_ecryptfs_desc - verify the description of a new/loaded encrypted key
+ *
+ * The description of a encrypted key with format 'ecryptfs' must contain
+ * exactly 16 hexadecimal characters.
+ *
+ */
+static int valid_ecryptfs_desc(const char *ecryptfs_desc)
+{
+	int i;
+
+	if (strlen(ecryptfs_desc) != KEY_ECRYPTFS_DESC_LEN) {
+		pr_err("encrypted_key: key description must be %d hexadecimal "
+		       "characters long\n", KEY_ECRYPTFS_DESC_LEN);
+		return -EINVAL;
+	}
+
+	for (i = 0; i < KEY_ECRYPTFS_DESC_LEN; i++) {
+		if (!isxdigit(ecryptfs_desc[i])) {
+			pr_err("encrypted_key: key description must contain "
+			       "only hexadecimal characters\n");
+			return -EINVAL;
+		}
+	}
+
+	return 0;
+}
+
+/*
  * valid_master_desc - verify the 'key-type:desc' of a new/updated master-key
  *
  * key-type:= "trusted:" | "user:"
@@ -158,7 +191,7 @@ static int datablob_parse(char *datablob, const char **format,
 	}
 	key_cmd = match_token(keyword, key_tokens, args);
 
-	/* Get optional format: default */
+	/* Get optional format: default | ecryptfs */
 	p = strsep(&datablob, " \t");
 	if (!p) {
 		pr_err("encrypted_key: insufficient parameters specified\n");
@@ -167,6 +200,7 @@ static int datablob_parse(char *datablob, const char **format,
 
 	key_format = match_token(p, key_format_tokens, args);
 	switch (key_format) {
+	case Opt_ecryptfs:
 	case Opt_default:
 		*format = p;
 		*master_desc = strsep(&datablob, " \t");
@@ -601,6 +635,17 @@ static struct encrypted_key_payload *encrypted_key_alloc(struct key *key,
 	format_len = (!format) ? strlen(key_format_default) : strlen(format);
 	decrypted_datalen = dlen;
 	payload_datalen = decrypted_datalen;
+	if (format && !strcmp(format, key_format_ecryptfs)) {
+		if (dlen != ECRYPTFS_MAX_KEY_BYTES) {
+			pr_err("encrypted_key: keylen for the ecryptfs format "
+			       "must be equal to %d bytes\n",
+			       ECRYPTFS_MAX_KEY_BYTES);
+			return ERR_PTR(-EINVAL);
+		}
+		decrypted_datalen = ECRYPTFS_MAX_KEY_BYTES;
+		payload_datalen = sizeof(struct ecryptfs_auth_tok);
+	}
+
 	encrypted_datalen = roundup(decrypted_datalen, blksize);
 
 	datablob_len = format_len + 1 + strlen(master_desc) + 1
@@ -686,8 +731,14 @@ static void __ekey_init(struct encrypted_key_payload *epayload,
 
 	if (!format)
 		memcpy(epayload->format, key_format_default, format_len);
-	else
+	else {
+		if (!strcmp(format, key_format_ecryptfs))
+			epayload->decrypted_data =
+				ecryptfs_get_auth_tok_key((struct ecryptfs_auth_tok *)epayload->payload_data);
+
 		memcpy(epayload->format, format, format_len);
+	}
+
 	memcpy(epayload->master_desc, master_desc, strlen(master_desc));
 	memcpy(epayload->datalen, datalen, strlen(datalen));
 }
@@ -699,11 +750,21 @@ static void __ekey_init(struct encrypted_key_payload *epayload,
  * itself.  For an old key, decrypt the hex encoded data.
  */
 static int encrypted_init(struct encrypted_key_payload *epayload,
-			  const char *format, const char *master_desc,
-			  const char *datalen, const char *hex_encoded_iv)
+			  const char *key_desc, const char *format,
+			  const char *master_desc, const char *datalen,
+			  const char *hex_encoded_iv)
 {
 	int ret = 0;
 
+	if (format && !strcmp(format, key_format_ecryptfs)) {
+		ret = valid_ecryptfs_desc(key_desc);
+		if (ret < 0)
+			return ret;
+
+		ecryptfs_fill_auth_tok((struct ecryptfs_auth_tok *)epayload->payload_data,
+				       key_desc);
+	}
+
 	__ekey_init(epayload, format, master_desc, datalen);
 	if (!hex_encoded_iv) {
 		get_random_bytes(epayload->iv, ivsize);
@@ -753,8 +814,8 @@ static int encrypted_instantiate(struct key *key, const void *data,
 		ret = PTR_ERR(epayload);
 		goto out;
 	}
-	ret = encrypted_init(epayload, format, master_desc, decrypted_datalen,
-			     hex_encoded_iv);
+	ret = encrypted_init(epayload, key->description, format, master_desc,
+			     decrypted_datalen, hex_encoded_iv);
 	if (ret < 0) {
 		kfree(epayload);
 		goto out;