keys-encrypted: add nvdimm key format type to encrypted keys

Adding nvdimm key format type to encrypted keys in order to limit the size
of the key to 32bytes.

Signed-off-by: Dave Jiang <dave.jiang@intel.com>
Acked-by: Mimi Zohar <zohar@linux.ibm.com>
Signed-off-by: Dan Williams <dan.j.williams@intel.com>

Documentation/security/keys/trusted-encrypted.rst

@@ -76,7 +76,7 @@ Usage::
 
 Where::
 
-	format:= 'default | ecryptfs'
+	format:= 'default | ecryptfs | enc32'
 	key-type:= 'trusted' | 'user'
 
 
@@ -173,3 +173,7 @@ are anticipated.  In particular the new format 'ecryptfs' has been defined in
 in order to use encrypted keys to mount an eCryptfs filesystem.  More details
 about the usage can be found in the file
 ``Documentation/security/keys/ecryptfs.rst``.
+
+Another new format 'enc32' has been defined in order to support encrypted keys
+with payload size of 32 bytes. This will initially be used for nvdimm security
+but may expand to other usages that require 32 bytes payload.

security/keys/encrypted-keys/encrypted.c

@@ -45,6 +45,7 @@ static const char hmac_alg[] = "hmac(sha256)";
 static const char blkcipher_alg[] = "cbc(aes)";
 static const char key_format_default[] = "default";
 static const char key_format_ecryptfs[] = "ecryptfs";
+static const char key_format_enc32[] = "enc32";
 static unsigned int ivsize;
 static int blksize;
 
@@ -54,6 +55,7 @@ static int blksize;
 #define HASH_SIZE SHA256_DIGEST_SIZE
 #define MAX_DATA_SIZE 4096
 #define MIN_DATA_SIZE  20
+#define KEY_ENC32_PAYLOAD_LEN 32
 
 static struct crypto_shash *hash_tfm;
 
@@ -62,12 +64,13 @@ enum {
 };
 
 enum {
-	Opt_error = -1, Opt_default, Opt_ecryptfs
+	Opt_error = -1, Opt_default, Opt_ecryptfs, Opt_enc32
 };
 
 static const match_table_t key_format_tokens = {
 	{Opt_default, "default"},
 	{Opt_ecryptfs, "ecryptfs"},
+	{Opt_enc32, "enc32"},
 	{Opt_error, NULL}
 };
 
@@ -195,6 +198,7 @@ static int datablob_parse(char *datablob, const char **format,
 	key_format = match_token(p, key_format_tokens, args);
 	switch (key_format) {
 	case Opt_ecryptfs:
+	case Opt_enc32:
 	case Opt_default:
 		*format = p;
 		*master_desc = strsep(&datablob, " \t");
@@ -625,15 +629,22 @@ 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 (format && !strcmp(format, key_format_ecryptfs)) {
-		if (dlen != ECRYPTFS_MAX_KEY_BYTES) {
-			pr_err("encrypted_key: keylen for the ecryptfs format "
-			       "must be equal to %d bytes\n",
-			       ECRYPTFS_MAX_KEY_BYTES);
-			return ERR_PTR(-EINVAL);
+	if (format) {
+		if (!strcmp(format, key_format_ecryptfs)) {
+			if (dlen != ECRYPTFS_MAX_KEY_BYTES) {
+				pr_err("encrypted_key: keylen for the ecryptfs format must be equal to %d bytes\n",
+					ECRYPTFS_MAX_KEY_BYTES);
+				return ERR_PTR(-EINVAL);
+			}
+			decrypted_datalen = ECRYPTFS_MAX_KEY_BYTES;
+			payload_datalen = sizeof(struct ecryptfs_auth_tok);
+		} else if (!strcmp(format, key_format_enc32)) {
+			if (decrypted_datalen != KEY_ENC32_PAYLOAD_LEN) {
+				pr_err("encrypted_key: enc32 key payload incorrect length: %d\n",
+						decrypted_datalen);
+				return ERR_PTR(-EINVAL);
+			}
 		}
-		decrypted_datalen = ECRYPTFS_MAX_KEY_BYTES;
-		payload_datalen = sizeof(struct ecryptfs_auth_tok);
 	}
 
 	encrypted_datalen = roundup(decrypted_datalen, blksize);