[PATCH v4] KEYS: encrypted: Instantiate key with user-provided decrypted data
Sumit Garg
sumit.garg at linaro.org
Thu Dec 30 10:07:21 UTC 2021
+ Jan, Ahmad
On Thu, 30 Dec 2021 at 03:24, Yael Tiomkin <yaelt at google.com> wrote:
>
> 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 instantiate encrypted keys using
> user-provided decrypted data, and therefore allows to perform key
> encryption from userspace. The decrypted key material will be
> inaccessible from userspace.
This type of user-space key import feature has already been discussed
at large in the context of trusted keys here [1]. So what makes it
special in case of encrypted keys such that it isn't a "UNSAFE_IMPORT"
or "DEBUGGING_IMPORT" or "DEVELOPMENT_IMPORT", ...?
[1] https://lore.kernel.org/linux-integrity/74830d4f-5a76-8ba8-aad0-0d79f7c01af9@pengutronix.de/
-Sumit
>
> Reviewed-by: Mimi Zohar <zohar at linux.ibm.com>
> Signed-off-by: Yael Tiomkin <yaelt at google.com>
> ---
>
> Notes:
> v -> v2: fixed compilation error.
>
> v2 -> v3: modified documentation.
>
> v3 -> v4: modified commit message.
>
> .../security/keys/trusted-encrypted.rst | 25 ++++++--
> security/keys/encrypted-keys/encrypted.c | 62 +++++++++++++------
> 2 files changed, 63 insertions(+), 24 deletions(-)
>
> diff --git a/Documentation/security/keys/trusted-encrypted.rst b/Documentation/security/keys/trusted-encrypted.rst
> index 80d5a5af62a1..f614dad7de12 100644
> --- a/Documentation/security/keys/trusted-encrypted.rst
> +++ b/Documentation/security/keys/trusted-encrypted.rst
> @@ -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
> diff --git a/security/keys/encrypted-keys/encrypted.c b/security/keys/encrypted-keys/encrypted.c
> index 87432b35d771..baf6fba5e05e 100644
> --- a/security/keys/encrypted-keys/encrypted.c
> +++ b/security/keys/encrypted-keys/encrypted.c
> @@ -159,6 +159,7 @@ static int valid_master_desc(const char *new_desc, const char *orig_desc)
> *
> * 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 +171,7 @@ 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 +232,8 @@ 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 +598,8 @@ 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 +608,7 @@ 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 +618,20 @@ 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 (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 (!isalnum(decrypted_data[i])) {
> + pr_err("encrypted key: decrypted data provided must be alphanumeric\n");
> + return ERR_PTR(-EINVAL);
> + }
> + }
> + }
> +
> if (format) {
> if (!strcmp(format, key_format_ecryptfs)) {
> if (dlen != ECRYPTFS_MAX_KEY_BYTES) {
> @@ -740,13 +759,14 @@ 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 +780,26 @@ 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 +812,7 @@ 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 +825,18 @@ 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 +886,7 @@ 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 +895,7 @@ 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;
> --
> 2.34.1.448.ga2b2bfdf31-goog
>
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