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KEYS: encrypted: Instantiate key with user-provided decrypted data

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For availability and performance reasons master keys often need to be
released outside of a Key Management Service (KMS) to clients. It
would be beneficial to provide a mechanism where the
wrapping/unwrapping of data encryption keys (DEKs) is not dependent
on a remote call at runtime yet security is not (or only minimally)
compromised. Master keys could be securely stored in the Kernel and
be used to wrap/unwrap keys from Userspace.

The encrypted.c class supports instantiation of encrypted keys with
either an already-encrypted key material, or by generating new key
material based on random numbers. This patch defines a new datablob
format: [<format>] <master-key name> <decrypted data length>
<decrypted data> that allows to inject and encrypt user-provided
decrypted data. The decrypted data must be hex-ascii encoded.

Signed-off-by: Yael Tzur <yaelt@google.com>
Reviewed-by: Mimi Zohar <zohar@linux.ibm.com>
Reviewed-by: Sumit Garg <sumit.garg@linaro.org>
Reviewed-by: Jarkko Sakkinen <jarkko@kernel.org>
Signed-off-by: Mimi Zohar <zohar@linux.ibm.com>
This commit is contained in:
Yael Tzur 2022-02-15 09:19:53 -05:00 committed by Mimi Zohar
parent 8c54135e2e
commit cd3bc044af
3 changed files with 86 additions and 29 deletions
repo.diff.show_diff_stats Download patch file Download diff file Expand all files Collapse all files

25
Documentation/security/keys/trusted-encrypted.rst
View file

@ -107,12 +107,13 @@ Encrypted Keys
--------------
Encrypted keys do not depend on a trust source, and are faster, as they use AES
for encryption/decryption. New keys are created from kernel-generated random
numbers, and are encrypted/decrypted using a specified ‘master’ key. The
‘master’ key can either be a trusted-key or user-key type. The main disadvantage
of encrypted keys is that if they are not rooted in a trusted key, they are only
as secure as the user key encrypting them. The master user key should therefore
be loaded in as secure a way as possible, preferably early in boot.
for encryption/decryption. New keys are created either from kernel-generated
random numbers or user-provided decrypted data, and are encrypted/decrypted
using a specified ‘master’ key. The ‘master’ key can either be a trusted-key or
user-key type. The main disadvantage of encrypted keys is that if they are not
rooted in a trusted key, they are only as secure as the user key encrypting
them. The master user key should therefore be loaded in as secure a way as
possible, preferably early in boot.
Usage
@ -199,6 +200,8 @@ Usage::
keyctl add encrypted name "new [format] key-type:master-key-name keylen"
ring
keyctl add encrypted name "new [format] key-type:master-key-name keylen
decrypted-data" ring
keyctl add encrypted name "load hex_blob" ring
keyctl update keyid "update key-type:master-key-name"
@ -303,6 +306,16 @@ Load an encrypted key "evm" from saved blob::
82dbbc55be2a44616e4959430436dc4f2a7a9659aa60bb4652aeb2120f149ed197c564e0
24717c64 5972dcb82ab2dde83376d82b2e3c09ffc
Instantiate an encrypted key "evm" using user-provided decrypted data::
$ keyctl add encrypted evm "new default user:kmk 32 `cat evm_decrypted_data.blob`" @u
794890253
$ keyctl print 794890253
default user:kmk 32 2375725ad57798846a9bbd240de8906f006e66c03af53b1b382d
bbc55be2a44616e4959430436dc4f2a7a9659aa60bb4652aeb2120f149ed197c564e0247
17c64 5972dcb82ab2dde83376d82b2e3c09ffc
Other uses for trusted and encrypted keys, such as for disk and file encryption
are anticipated. In particular the new format 'ecryptfs' has been defined
in order to use encrypted keys to mount an eCryptfs filesystem. More details

19
security/keys/Kconfig
View file

@ -98,10 +98,21 @@ config ENCRYPTED_KEYS
select CRYPTO_RNG
help
This option provides support for create/encrypting/decrypting keys
in the kernel. Encrypted keys are kernel generated random numbers,
which are encrypted/decrypted with a 'master' symmetric key. The
'master' key can be either a trusted-key or user-key type.
Userspace only ever sees/stores encrypted blobs.
in the kernel. Encrypted keys are instantiated using kernel
generated random numbers or provided decrypted data, and are
encrypted/decrypted with a 'master' symmetric key. The 'master'
key can be either a trusted-key or user-key type. Only encrypted
blobs are ever output to Userspace.
If you are unsure as to whether this is required, answer N.
config USER_DECRYPTED_DATA
bool "Allow encrypted keys with user decrypted data"
depends on ENCRYPTED_KEYS
help
This option provides support for instantiating encrypted keys using
user-provided decrypted data. The decrypted data must be hex-ascii
encoded.
If you are unsure as to whether this is required, answer N.

71
security/keys/encrypted-keys/encrypted.c
View file

@ -78,6 +78,11 @@ static const match_table_t key_tokens = {
{Opt_err, NULL}
};
static bool user_decrypted_data = IS_ENABLED(CONFIG_USER_DECRYPTED_DATA);
module_param(user_decrypted_data, bool, 0);
MODULE_PARM_DESC(user_decrypted_data,
"Allow instantiation of encrypted keys using provided decrypted data");
static int aes_get_sizes(void)
{
struct crypto_skcipher *tfm;
@ -158,7 +163,7 @@ static int valid_master_desc(const char *new_desc, const char *orig_desc)
* datablob_parse - parse the keyctl data
*
* datablob format:
* new [<format>] <master-key name> <decrypted data length>
* new [<format>] <master-key name> <decrypted data length> [<decrypted data>]
* load [<format>] <master-key name> <decrypted data length>
* <encrypted iv + data>
* update <new-master-key name>
@ -170,7 +175,7 @@ static int valid_master_desc(const char *new_desc, const char *orig_desc)
*/
static int datablob_parse(char *datablob, const char **format,
char **master_desc, char **decrypted_datalen,
char **hex_encoded_iv)
char **hex_encoded_iv, char **decrypted_data)
{
substring_t args[MAX_OPT_ARGS];
int ret = -EINVAL;
@ -231,6 +236,7 @@ static int datablob_parse(char *datablob, const char **format,
"when called from .update method\n", keyword);
break;
}
*decrypted_data = strsep(&datablob, " \t");
ret = 0;
break;
case Opt_load:
@ -595,7 +601,8 @@ static int derived_key_decrypt(struct encrypted_key_payload *epayload,
static struct encrypted_key_payload *encrypted_key_alloc(struct key *key,
const char *format,
const char *master_desc,
const char *datalen)
const char *datalen,
const char *decrypted_data)
{
struct encrypted_key_payload *epayload = NULL;
unsigned short datablob_len;
@ -604,6 +611,7 @@ static struct encrypted_key_payload *encrypted_key_alloc(struct key *key,
unsigned int encrypted_datalen;
unsigned int format_len;
long dlen;
int i;
int ret;
ret = kstrtol(datalen, 10, &dlen);
@ -613,6 +621,24 @@ 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 (decrypted_data) {
if (!user_decrypted_data) {
pr_err("encrypted key: instantiation of keys using provided decrypted data is disabled since CONFIG_USER_DECRYPTED_DATA is set to false\n");
return ERR_PTR(-EINVAL);
}
if (strlen(decrypted_data) != decrypted_datalen) {
pr_err("encrypted key: decrypted data provided does not match decrypted data length provided\n");
return ERR_PTR(-EINVAL);
}
for (i = 0; i < strlen(decrypted_data); i++) {
if (!isxdigit(decrypted_data[i])) {
pr_err("encrypted key: decrypted data provided must contain only hexadecimal characters\n");
return ERR_PTR(-EINVAL);
}
}
}
if (format) {
if (!strcmp(format, key_format_ecryptfs)) {
if (dlen != ECRYPTFS_MAX_KEY_BYTES) {
@ -740,13 +766,14 @@ static void __ekey_init(struct encrypted_key_payload *epayload,
/*
* encrypted_init - initialize an encrypted key
*
* For a new key, use a random number for both the iv and data
* itself. For an old key, decrypt the hex encoded data.
* For a new key, use either a random number or user-provided decrypted data in
* case it is provided. A random number is used for the iv in both cases. For
* an old key, decrypt the hex encoded data.
*/
static int encrypted_init(struct encrypted_key_payload *epayload,
const char *key_desc, const char *format,
const char *master_desc, const char *datalen,
const char *hex_encoded_iv)
const char *hex_encoded_iv, const char *decrypted_data)
{
int ret = 0;
@ -760,21 +787,26 @@ static int encrypted_init(struct encrypted_key_payload *epayload,
}
__ekey_init(epayload, format, master_desc, datalen);
if (!hex_encoded_iv) {
get_random_bytes(epayload->iv, ivsize);
get_random_bytes(epayload->decrypted_data,
epayload->decrypted_datalen);
} else
if (hex_encoded_iv) {
ret = encrypted_key_decrypt(epayload, format, hex_encoded_iv);
} else if (decrypted_data) {
get_random_bytes(epayload->iv, ivsize);
memcpy(epayload->decrypted_data, decrypted_data,
epayload->decrypted_datalen);
} else {
get_random_bytes(epayload->iv, ivsize);
get_random_bytes(epayload->decrypted_data, epayload->decrypted_datalen);
}
return ret;
}
/*
* encrypted_instantiate - instantiate an encrypted key
*
* Decrypt an existing encrypted datablob or create a new encrypted key
* based on a kernel random number.
* Instantiates the key:
* - by decrypting an existing encrypted datablob, or
* - by creating a new encrypted key based on a kernel random number, or
* - using provided decrypted data.
*
* On success, return 0. Otherwise return errno.
*/
@ -787,6 +819,7 @@ static int encrypted_instantiate(struct key *key,
char *master_desc = NULL;
char *decrypted_datalen = NULL;
char *hex_encoded_iv = NULL;
char *decrypted_data = NULL;
size_t datalen = prep->datalen;
int ret;
@ -799,18 +832,18 @@ static int encrypted_instantiate(struct key *key,
datablob[datalen] = 0;
memcpy(datablob, prep->data, datalen);
ret = datablob_parse(datablob, &format, &master_desc,
&decrypted_datalen, &hex_encoded_iv);
&decrypted_datalen, &hex_encoded_iv, &decrypted_data);
if (ret < 0)
goto out;
epayload = encrypted_key_alloc(key, format, master_desc,
decrypted_datalen);
decrypted_datalen, decrypted_data);
if (IS_ERR(epayload)) {
ret = PTR_ERR(epayload);
goto out;
}
ret = encrypted_init(epayload, key->description, format, master_desc,
decrypted_datalen, hex_encoded_iv);
decrypted_datalen, hex_encoded_iv, decrypted_data);
if (ret < 0) {
kfree_sensitive(epayload);
goto out;
@ -860,7 +893,7 @@ static int encrypted_update(struct key *key, struct key_preparsed_payload *prep)
buf[datalen] = 0;
memcpy(buf, prep->data, datalen);
ret = datablob_parse(buf, &format, &new_master_desc, NULL, NULL);
ret = datablob_parse(buf, &format, &new_master_desc, NULL, NULL, NULL);
if (ret < 0)
goto out;
@ -869,7 +902,7 @@ static int encrypted_update(struct key *key, struct key_preparsed_payload *prep)
goto out;
new_epayload = encrypted_key_alloc(key, epayload->format,
new_master_desc, epayload->datalen);
new_master_desc, epayload->datalen, NULL);
if (IS_ERR(new_epayload)) {
ret = PTR_ERR(new_epayload);
goto out;