CVE-2021-3979 (Python, published 2022-08-25T20:15Z)
Description: value: A key length flaw was found in Red Hat Ceph Storage. An attacker can exploit the fact that the key length is incorrectly passed in an encryption algorithm to create a non random key, which is weaker and can be exploited for loss of confidentiality and integrity on encrypted disks.
Severity: nan (CVSS v3 base score: 6.5)
Weakness: CWE-287 \u2014 Improper Authentication
When an actor claims to have a given identity, the product does not prove or insufficiently proves that the claim is correct.
Repository: https://github.com/ceph/ceph
Files changed:
src/ceph-volume/ceph_volume/tests/util/test_encryption.py
src/ceph-volume/ceph_volume/util/encryption.py
Commit message: ceph-volume: honour osd_dmcrypt_key_size option

ceph-volume doesn't honour osd_dmcrypt_key_size.
It means the default size is always applied.

It also changes the default value in `get_key_size_from_conf()`

From cryptsetup manpage:

> For XTS mode you can optionally set a key size of 512 bits with the -s option.

Using more than 512bits will end up with the following error message:

```
Key size in XTS mode must be 256 or 512 bits.
```

Fixes: https://tracker.ceph.com/issues/54006

Signed-off-by: Guillaume Abrioux <gabrioux@redhat.com>


Vulnerable code:
    def test_dmcrypt_with_default_size(self, conf_ceph_stub):
        conf_ceph_stub('[global]\nfsid=asdf-lkjh')
        result = encryption.create_dmcrypt_key()
        assert len(result) == 172

    def test_dmcrypt_with_custom_size(self, conf_ceph_stub):
        conf_ceph_stub('''
        [global]
        fsid=asdf
        [osd]
        osd_dmcrypt_size=8
        ''')
        assert len(result) == 172

def create_dmcrypt_key():
    Create the secret dm-crypt key used to decrypt a device.
    # get the customizable dmcrypt key size (in bits) from ceph.conf fallback
    # to the default of 1024
    dmcrypt_key_size = conf.ceph.get_safe(
        default=1024,
    )
    # The size of the key is defined in bits, so we must transform that
    # value to bytes (dividing by 8) because we read in bytes, not bits
    random_string = os.urandom(int(dmcrypt_key_size / 8))

Fixed code:
import base64
class TestGetKeySize(object):
    def test_get_size_from_conf_default(self, conf_ceph_stub):
        conf_ceph_stub('''
        [global]
        fsid=asdf
        ''')
        assert encryption.get_key_size_from_conf() == '512'

    def test_get_size_from_conf_custom(self, conf_ceph_stub):
        conf_ceph_stub('''
        [global]
        fsid=asdf
        [osd]
        osd_dmcrypt_key_size=256
        ''')
        assert encryption.get_key_size_from_conf() == '256'

    def test_get_size_from_conf_custom_invalid(self, conf_ceph_stub):
        conf_ceph_stub('''
        [global]
        fsid=asdf
        [osd]
        osd_dmcrypt_key_size=1024
        ''')
        assert encryption.get_key_size_from_conf() == '512'
    def test_dmcrypt(self):
        assert len(base64.b64decode(result)) == 128
def get_key_size_from_conf():
    Return the osd dmcrypt key size from config file.
    Default is 512.
    default_key_size = '512'
    key_size = conf.ceph.get_safe(
        default='512')

    if key_size not in ['256', '512']:
        logger.warning(("Invalid value set for osd_dmcrypt_key_size ({}). "
                        "Falling back to {}bits".format(key_size, default_key_size)))
        return default_key_size

    return key_size

def create_dmcrypt_key():
    """
    Create the secret dm-crypt key (KEK) used to encrypt/decrypt the Volume Key.
    """
    random_string = os.urandom(128)
        '--key-size',
        get_key_size_from_conf(),
        '--key-size',
        get_key_size_from_conf(),