[dm-devel] [PATCH v2] dm-crypt: add ability to use keys from the kernel key retention service
Ondrej Kozina
okozina at redhat.com
Wed Nov 16 20:47:11 UTC 2016
(Please still consider it to be RFC only, I need to modify the uspace teststuite
again due to changes in key_string format. Also the changes to dm-crypt documentation
will follow before final submit. Feature wide I'd consider the patch being complete
unless any bugs would emerge)
The kernel key service is a generic way to store keys for the use of
other subsystems. Currently there is no way to use kernel keys in dm-crypt.
This patch aims to fix that. Instead of key userspace may pass a key
description with preceding ':'. So message that constructs encryption
mapping now looks like this:
<cipher> [<key>|:<key_string>] <iv_offset> <dev_path> <start> [<#opt_params> <opt_params>]
where <key_string> is in format: <key_size>:<key_type>:<key_description>
Currently we only support two elementary key types: 'user' and 'logon'.
Keys may be loaded in dm-crypt either via <key_string> or using
classical method and pass the key in hex representation directly.
dm-crypt device initialised with a key passed in hex representation may be
replaced with key passed in key_string format and vice versa.
(Patch is based on original work by Andrey Ryabinin)
Signed-off-by: Ondrej Kozina <okozina at redhat.com>
---
drivers/md/dm-crypt.c | 167 ++++++++++++++++++++++++++++++++++++++++++++------
1 file changed, 148 insertions(+), 19 deletions(-)
diff --git a/drivers/md/dm-crypt.c b/drivers/md/dm-crypt.c
index 0aedd0e..f4189ca 100644
--- a/drivers/md/dm-crypt.c
+++ b/drivers/md/dm-crypt.c
@@ -12,6 +12,7 @@
#include <linux/module.h>
#include <linux/init.h>
#include <linux/kernel.h>
+#include <linux/key.h>
#include <linux/bio.h>
#include <linux/blkdev.h>
#include <linux/mempool.h>
@@ -29,6 +30,7 @@
#include <crypto/md5.h>
#include <crypto/algapi.h>
#include <crypto/skcipher.h>
+#include <keys/user-type.h>
#include <linux/device-mapper.h>
@@ -140,6 +142,7 @@ struct crypt_config {
char *cipher;
char *cipher_string;
+ char *key_string;
struct crypt_iv_operations *iv_gen_ops;
union {
@@ -1490,29 +1493,138 @@ static int crypt_setkey_allcpus(struct crypt_config *cc)
return err;
}
-static int crypt_set_key(struct crypt_config *cc, char *key)
+#ifdef CONFIG_KEYS
+static int crypt_set_keyring_key(struct crypt_config *cc, const char *key_string)
{
- int r = -EINVAL;
- int key_string_len = strlen(key);
+ char *new_key_string, *key_desc;
+ int ret;
+ struct key *key;
+ const struct user_key_payload *ukp;
- /* The key size may not be changed. */
- if (cc->key_size != (key_string_len >> 1))
+ /* look for next ':' separating key_type from key_description */
+ key_desc = strpbrk(key_string, ":");
+ if (!key_desc || key_desc == key_string || !strlen(key_desc + 1))
+ return -EINVAL;
+
+ if (strncmp(key_string, "logon", key_desc - key_string) &&
+ strncmp(key_string, "user", key_desc - key_string))
+ return -EINVAL;
+
+ new_key_string = kstrdup(key_string, GFP_KERNEL);
+ if (!new_key_string)
+ return -ENOMEM;
+
+ /*
+ * FIXME: are there any key descriptions we should disallow users
+ * from loading to dm-crypt? i.e.: kernel keys starting with '.'
+ */
+
+ key = request_key(strncmp(key_string, "user", 4) ? &key_type_logon : &key_type_user, key_desc + 1, NULL);
+ if (IS_ERR(key)) {
+ kzfree(new_key_string);
+ return PTR_ERR(key);
+ }
+
+ rcu_read_lock();
+ ret = key_validate(key);
+ if (ret < 0)
goto out;
- /* Hyphen (which gives a key_size of zero) means there is no key. */
- if (!cc->key_size && strcmp(key, "-"))
+ ukp = user_key_payload(key);
+ if (cc->key_size != ukp->datalen) {
+ ret = -EINVAL;
goto out;
+ }
+ memcpy(cc->key, ukp->data, cc->key_size);
+
+ rcu_read_unlock();
+ key_put(key);
/* clear the flag since following operations may invalidate previously valid key */
clear_bit(DM_CRYPT_KEY_VALID, &cc->flags);
- if (cc->key_size && crypt_decode_key(cc->key, key, cc->key_size) < 0)
- goto out;
+ ret = crypt_setkey_allcpus(cc);
- r = crypt_setkey_allcpus(cc);
- if (!r)
+ /* wipe the kernel key payload in each case */
+ memset(cc->key, 0, cc->key_size * sizeof(u8));
+
+ if (!ret) {
set_bit(DM_CRYPT_KEY_VALID, &cc->flags);
+ kzfree(cc->key_string);
+ cc->key_string = new_key_string;
+ } else
+ kzfree(new_key_string);
+
+ return ret;
+out:
+ rcu_read_unlock();
+ key_put(key);
+ kzfree(new_key_string);
+ return ret;
+}
+
+static int get_key_size(char **key_string)
+{
+ char *colon, dummy;
+ int ret;
+
+ if (*key_string[0] != ':')
+ return strlen(*key_string) >> 1;
+ /* look for next ':' in key string */
+ colon = strpbrk(*key_string + 1, ":");
+ if (!colon)
+ return -EINVAL;
+
+ if (sscanf(*key_string + 1, "%u%c", &ret, &dummy) != 2 || dummy != ':')
+ return -EINVAL;
+
+ *key_string = colon;
+
+ /* remaining key string should be :<logon|user>:<key_desc> */
+
+ return ret;
+}
+#else
+static int crypt_set_keyring_key(struct crypt_config *cc, const char *key_desc)
+{
+ return -EINVAL;
+}
+
+static int get_key_size(char **key)
+{
+ return (*key[0] == ':') ? -EINVAL : strlen(*key) >> 1;
+}
+#endif
+
+static int crypt_set_key(struct crypt_config *cc, char *key)
+{
+ int r = -EINVAL;
+ int key_string_len = strlen(key);
+
+ /* Hyphen (which gives a key_size of zero) means there is no key. */
+ if (!cc->key_size && strcmp(key, "-"))
+ goto out;
+
+ /* ':' means that the key is in kernel keyring */
+ if (key[0] == ':')
+ r = crypt_set_keyring_key(cc, key + 1);
+ else {
+ /* clear the flag since following operations may invalidate previously valid key */
+ clear_bit(DM_CRYPT_KEY_VALID, &cc->flags);
+
+ /* wipe references to any kernel keyring key */
+ kzfree(cc->key_string);
+ cc->key_string = NULL;
+
+ if (cc->key_size &&
+ crypt_decode_key(cc->key, key, cc->key_size) < 0)
+ goto out;
+
+ r = crypt_setkey_allcpus(cc);
+ if (!r)
+ set_bit(DM_CRYPT_KEY_VALID, &cc->flags);
+ }
out:
/* Hex key string not needed after here, so wipe it. */
memset(key, '0', key_string_len);
@@ -1524,6 +1636,8 @@ static int crypt_wipe_key(struct crypt_config *cc)
{
clear_bit(DM_CRYPT_KEY_VALID, &cc->flags);
memset(&cc->key, 0, cc->key_size * sizeof(u8));
+ kzfree(cc->key_string);
+ cc->key_string = NULL;
return crypt_setkey_allcpus(cc);
}
@@ -1561,6 +1675,7 @@ static void crypt_dtr(struct dm_target *ti)
kzfree(cc->cipher);
kzfree(cc->cipher_string);
+ kzfree(cc->key_string);
/* Must zero key material before freeing */
kzfree(cc);
@@ -1729,12 +1844,13 @@ static int crypt_ctr_cipher(struct dm_target *ti,
/*
* Construct an encryption mapping:
- * <cipher> <key> <iv_offset> <dev_path> <start>
+ * <cipher> [<key>|:<key_size>:<user|logon>:<key_description>] <iv_offset> <dev_path> <start>
*/
static int crypt_ctr(struct dm_target *ti, unsigned int argc, char **argv)
{
struct crypt_config *cc;
- unsigned int key_size, opt_params;
+ int key_size;
+ unsigned int opt_params;
unsigned long long tmpll;
int ret;
size_t iv_size_padding;
@@ -1751,7 +1867,11 @@ static int crypt_ctr(struct dm_target *ti, unsigned int argc, char **argv)
return -EINVAL;
}
- key_size = strlen(argv[1]) >> 1;
+ key_size = get_key_size(&argv[1]);
+ if (key_size < 0) {
+ ti->error = "Cannot parse key size";
+ return -EINVAL;
+ }
cc = kzalloc(sizeof(*cc) + key_size * sizeof(u8), GFP_KERNEL);
if (!cc) {
@@ -1958,10 +2078,13 @@ static void crypt_status(struct dm_target *ti, status_type_t type,
case STATUSTYPE_TABLE:
DMEMIT("%s ", cc->cipher_string);
- if (cc->key_size > 0)
- for (i = 0; i < cc->key_size; i++)
- DMEMIT("%02x", cc->key[i]);
- else
+ if (cc->key_size > 0) {
+ if (cc->key_string)
+ DMEMIT(":%u:%s", cc->key_size, cc->key_string);
+ else
+ for (i = 0; i < cc->key_size; i++)
+ DMEMIT("%02x", cc->key[i]);
+ } else
DMEMIT("-");
DMEMIT(" %llu %s %llu", (unsigned long long)cc->iv_offset,
@@ -2028,6 +2151,12 @@ static int crypt_message(struct dm_target *ti, unsigned argc, char **argv)
return -EINVAL;
}
if (argc == 3 && !strcasecmp(argv[1], "set")) {
+ /* The key size may not be changed. */
+ if (cc->key_size != get_key_size(&argv[2])) {
+ memset(argv[2], '0', strlen(argv[2]));
+ return -EINVAL;
+ }
+
ret = crypt_set_key(cc, argv[2]);
if (ret)
return ret;
@@ -2071,7 +2200,7 @@ static void crypt_io_hints(struct dm_target *ti, struct queue_limits *limits)
static struct target_type crypt_target = {
.name = "crypt",
- .version = {1, 14, 1},
+ .version = {1, 15, 0},
.module = THIS_MODULE,
.ctr = crypt_ctr,
.dtr = crypt_dtr,
--
2.7.4
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