[PATCH v4] KEYS: encrypted: Instantiate key with user-provided decrypted data
Nayna
nayna at linux.vnet.ibm.com
Thu Jan 20 17:13:33 UTC 2022
On 1/13/22 14:01, Yael Tiomkin wrote:
> On Mon, Jan 10, 2022 at 11:04 AM Nayna <nayna at linux.vnet.ibm.com> wrote:
>>
>> On 12/29/21 16:53, Yael Tiomkin 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.
>>>
>>> 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])) {
>> User-provided decrypted data may have special characters, commonly used
>> in passwords or key phrases, apart from alphanumeric. Replace isalnum
>> with !iscntrl() to validate against control characters but allow special
>> characters.
>>
>> Thanks & Regards,
>>
>> - Nayna
>>
> Hi Nayna,
> I wonder if we should use isprint() instead?
I have been thinking more about this. Encrypted keys documentation says,
"All user level blobs, are displayed and loaded in hex ascii for
convenience."
Should we use a similar hex ascii encoding for user-provided data?
Verification would then be isxdigit().
Users should convert their input to hex ascii before passing it to keyctl.
Thanks & Regards,
- Nayna
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