keys: add new key-type encrypted

Define a new kernel key-type called 'encrypted'. Encrypted keys are kernel
generated random numbers, which are encrypted/decrypted with a 'trusted'
symmetric key. Encrypted keys are created/encrypted/decrypted in the kernel.
Userspace only ever sees/stores encrypted blobs.

Changelog:
- bug fix: replaced master-key rcu based locking with semaphore
  (reported by David Howells)
- Removed memset of crypto_shash_digest() digest output
- Replaced verification of 'key-type:key-desc' using strcspn(), with
  one based on string constants.
- Moved documentation to Documentation/keys-trusted-encrypted.txt
- Replace hash with shash (based on comments by David Howells)
- Make lengths/counts size_t where possible (based on comments by David Howells)
  Could not convert most lengths, as crypto expects 'unsigned int'
  (size_t: on 32 bit is defined as unsigned int, but on 64 bit is unsigned long)
- Add 'const' where possible (based on comments by David Howells)
- allocate derived_buf dynamically to support arbitrary length master key
  (fixed by Roberto Sassu)
- wait until late_initcall for crypto libraries to be registered
- cleanup security/Kconfig
- Add missing 'update' keyword (reported/fixed by Roberto Sassu)
- Free epayload on failure to create key (reported/fixed by Roberto Sassu)
- Increase the data size limit (requested by Roberto Sassu)
- Crypto return codes are always 0 on success and negative on failure,
  remove unnecessary tests.
- Replaced kzalloc() with kmalloc()

Signed-off-by: Mimi Zohar <zohar@us.ibm.com>
Signed-off-by: David Safford <safford@watson.ibm.com>
Reviewed-by: Roberto Sassu <roberto.sassu@polito.it>
Signed-off-by: James Morris <jmorris@namei.org>

include/keys/encrypted-type.h

@@ -0,0 +1,29 @@
+/*
+ * Copyright (C) 2010 IBM Corporation
+ * Author: Mimi Zohar <zohar@us.ibm.com>
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, version 2 of the License.
+ */
+
+#ifndef _KEYS_ENCRYPTED_TYPE_H
+#define _KEYS_ENCRYPTED_TYPE_H
+
+#include <linux/key.h>
+#include <linux/rcupdate.h>
+
+struct encrypted_key_payload {
+	struct rcu_head rcu;
+	char *master_desc;	/* datablob: master key name */
+	char *datalen;		/* datablob: decrypted key length */
+	u8 *iv;			/* datablob: iv */
+	u8 *encrypted_data;	/* datablob: encrypted data */
+	unsigned short datablob_len;	/* length of datablob */
+	unsigned short decrypted_datalen;	/* decrypted data length */
+	u8 decrypted_data[0];	/* decrypted data +  datablob + hmac */
+};
+
+extern struct key_type key_type_encrypted;
+
+#endif /* _KEYS_ENCRYPTED_TYPE_H */