KEYS: Add payload preparsing opportunity prior to key instantiate or update

Give the key type the opportunity to preparse the payload prior to the
instantiation and update routines being called.  This is done with the
provision of two new key type operations:

	int (*preparse)(struct key_preparsed_payload *prep);
	void (*free_preparse)(struct key_preparsed_payload *prep);

If the first operation is present, then it is called before key creation (in
the add/update case) or before the key semaphore is taken (in the update and
instantiate cases).  The second operation is called to clean up if the first
was called.

preparse() is given the opportunity to fill in the following structure:

	struct key_preparsed_payload {
		char		*description;
		void		*type_data[2];
		void		*payload;
		const void	*data;
		size_t		datalen;
		size_t		quotalen;
	};

Before the preparser is called, the first three fields will have been cleared,
the payload pointer and size will be stored in data and datalen and the default
quota size from the key_type struct will be stored into quotalen.

The preparser may parse the payload in any way it likes and may store data in
the type_data[] and payload fields for use by the instantiate() and update()
ops.

The preparser may also propose a description for the key by attaching it as a
string to the description field.  This can be used by passing a NULL or ""
description to the add_key() system call or the key_create_or_update()
function.  This cannot work with request_key() as that required the description
to tell the upcall about the key to be created.

This, for example permits keys that store PGP public keys to generate their own
name from the user ID and public key fingerprint in the key.

The instantiate() and update() operations are then modified to look like this:

	int (*instantiate)(struct key *key, struct key_preparsed_payload *prep);
	int (*update)(struct key *key, struct key_preparsed_payload *prep);

and the new payload data is passed in *prep, whether or not it was preparsed.

Signed-off-by: David Howells <dhowells@redhat.com>
Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>

2 files changed, 37 insertions, 4 deletions

diff --git a/include/keys/user-type.h b/include/keys/user-type.h
index bc9ec1d7698c..5e452c84f1e6 100644
--- a/include/keys/user-type.h
+++ b/include/keys/user-type.h
@@ -35,8 +35,10 @@ struct user_key_payload {
 extern struct key_type key_type_user;
 extern struct key_type key_type_logon;
 
-extern int user_instantiate(struct key *key, const void *data, size_t datalen);
-extern int user_update(struct key *key, const void *data, size_t datalen);
+struct key_preparsed_payload;
+
+extern int user_instantiate(struct key *key, struct key_preparsed_payload *prep);
+extern int user_update(struct key *key, struct key_preparsed_payload *prep);
 extern int user_match(const struct key *key, const void *criterion);
 extern void user_revoke(struct key *key);
 extern void user_destroy(struct key *key);
diff --git a/include/linux/key-type.h b/include/linux/key-type.h
index f0c651cda7b0..518a53afb9ea 100644
--- a/include/linux/key-type.h
+++ b/include/linux/key-type.h
@@ -26,6 +26,27 @@ struct key_construction {
         struct key      *authkey;/* authorisation for key being constructed */
 };
 
+/*
+ * Pre-parsed payload, used by key add, update and instantiate.
+ *
+ * This struct will be cleared and data and datalen will be set with the data
+ * and length parameters from the caller and quotalen will be set from
+ * def_datalen from the key type.  Then if the preparse() op is provided by the
+ * key type, that will be called.  Then the struct will be passed to the
+ * instantiate() or the update() op.
+ *
+ * If the preparse() op is given, the free_preparse() op will be called to
+ * clear the contents.
+ */
+struct key_preparsed_payload {
+        char            *description;   /* Proposed key description (or NULL) */
+        void            *type_data[2];  /* Private key-type data */
+        void            *payload;       /* Proposed payload */
+        const void      *data;          /* Raw data */
+        size_t          datalen;        /* Raw datalen */
+        size_t          quotalen;       /* Quota length for proposed payload */
+};
+
 typedef int (*request_key_actor_t)(struct key_construction *key,
                                    const char *op, void *aux);
 
@@ -45,18 +66,28 @@ struct key_type {
         /* vet a description */
         int (*vet_description)(const char *description);
 
+        /* Preparse the data blob from userspace that is to be the payload,
+         * generating a proposed description and payload that will be handed to
+         * the instantiate() and update() ops.
+         */
+        int (*preparse)(struct key_preparsed_payload *prep);
+
+        /* Free a preparse data structure.
+         */
+        void (*free_preparse)(struct key_preparsed_payload *prep);
+
         /* instantiate a key of this type
          * - this method should call key_payload_reserve() to determine if the
          *   user's quota will hold the payload
          */
-        int (*instantiate)(struct key *key, const void *data, size_t datalen);
+        int (*instantiate)(struct key *key, struct key_preparsed_payload *prep);
 
         /* update a key of this type (optional)
          * - this method should call key_payload_reserve() to recalculate the
          *   quota consumption
          * - the key must be locked against read when modifying
          */
-        int (*update)(struct key *key, const void *data, size_t datalen);
+        int (*update)(struct key *key, struct key_preparsed_payload *prep);
 
         /* match a key against a description */
         int (*match)(const struct key *key, const void *desc);