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cryptsetup: optionally, see if empty password works for unlocking the file system

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This adds a new switch try-empty-password. If set and none of PKCS#11 or
key files work, it is attempted to unlock the volume with an empty
password, before the user is asked for a password.

Usecase: an installer generates an OS image on one system, which is the
booted up for the first time in a possibly different system. The image
is encrypted using a random volume key, but an empty password. A tool
that runs on first boot then queries the user for a password to set or
enrols the volume in the TPM, removing the empty password. (Of course, in
such a scenario it is important to never reuse the installer image on
multiple systems as they all will have the same volume key, but that's a
different question.)
This commit is contained in:
Lennart Poettering 2020-04-29 19:41:02 +02:00
parent 2424fb7e7b
commit 0ba6f85ed3
1 changed files with 44 additions and 6 deletions
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50
src/cryptsetup/cryptsetup.c
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@ -46,6 +46,7 @@ static int arg_key_slot = CRYPT_ANY_SLOT;
static unsigned arg_keyfile_size = 0;
static uint64_t arg_keyfile_offset = 0;
static bool arg_keyfile_erase = false;
static bool arg_try_empty_password = false;
static char *arg_hash = NULL;
static char *arg_header = NULL;
static unsigned arg_tries = 3;
@ -262,7 +263,20 @@ static int parse_one_option(const char *option) {
if (r < 0)
return log_oom();
} else if (!streq(option, "x-initrd.attach"))
} else if ((val = startswith(option, "try-empty-password="))) {
r = parse_boolean(val);
if (r < 0) {
log_error_errno(r, "Failed to parse %s, ignoring: %m", option);
return 0;
}
arg_try_empty_password = r;
} else if (streq(option, "try-empty-password"))
arg_try_empty_password = true;
else if (!streq(option, "x-initrd.attach"))
log_warning("Encountered unknown /etc/crypttab option '%s', ignoring.", option);
return 0;
@ -939,12 +953,36 @@ static int run(int argc, char *argv[]) {
for (tries = 0; arg_tries == 0 || tries < arg_tries; tries++) {
_cleanup_strv_free_erase_ char **passwords = NULL;
/* When we were able to acquire multiple keys, let's always process them in this order:
*
* 1. A key acquired via PKCS#11 token
* 2. The discovered key: i.e. key_data + key_data_size
* 3. The configured key: i.e. key_file + arg_keyfile_offset + arg_keyfile_size
* 4. The empty password, in case arg_try_empty_password is set
* 5. We enquire the user for a password
*/
if (!key_file && !key_data && !arg_pkcs11_uri) {
r = get_password(argv[2], argv[3], until, tries == 0 && !arg_verify, &passwords);
if (r == -EAGAIN)
continue;
if (r < 0)
return r;
if (arg_try_empty_password) {
/* Hmm, let's try an empty password now, but only once */
arg_try_empty_password = false;
key_data = strdup("");
if (!key_data)
return log_oom();
key_data_size = 0;
} else {
/* Ask the user for a passphrase only as last resort, if we have
* nothing else to check for */
r = get_password(argv[2], argv[3], until, tries == 0 && !arg_verify, &passwords);
if (r == -EAGAIN)
continue;
if (r < 0)
return r;
}
}
if (streq_ptr(arg_type, CRYPT_TCRYPT))