[PATCH] Keys: Allow in-kernel key requestor to pass auxiliary data to upcaller

The proposed NFS key type uses its own method of passing key requests to
userspace (upcalling) rather than invoking /sbin/request-key.  This is
because the responsible userspace daemon should already be running and will
be contacted through rpc_pipefs.

This patch permits the NFS filesystem to pass auxiliary data to the upcall
operation (struct key_type::request_key) so that the upcaller can use a
pre-existing communications channel more easily.

Signed-off-by: David Howells <dhowells@redhat.com>
Acked-By: Kevin Coffman <kwc@citi.umich.edu>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>

2 files changed, 65 insertions, 18 deletions

diff --git a/Documentation/keys-request-key.txt b/Documentation/keys-request-key.txt
index 22488d791168..c1f64fdf84cb 100644
--- a/Documentation/keys-request-key.txt
+++ b/Documentation/keys-request-key.txt
@@ -3,16 +3,23 @@
                               ===================
 
 The key request service is part of the key retention service (refer to
-Documentation/keys.txt). This document explains more fully how that the
-requesting algorithm works.
+Documentation/keys.txt).  This document explains more fully how the requesting
+algorithm works.
 
 The process starts by either the kernel requesting a service by calling
-request_key():
+request_key*():
 
         struct key *request_key(const struct key_type *type,
                                 const char *description,
                                 const char *callout_string);
 
+or:
+
+        struct key *request_key_with_auxdata(const struct key_type *type,
+                                             const char *description,
+                                             const char *callout_string,
+                                             void *aux);
+
 Or by userspace invoking the request_key system call:
 
         key_serial_t request_key(const char *type,
@@ -20,16 +27,26 @@ Or by userspace invoking the request_key system call:
                                  const char *callout_info,
                                  key_serial_t dest_keyring);
 
-The main difference between the two access points is that the in-kernel
-interface does not need to link the key to a keyring to prevent it from being
-immediately destroyed. The kernel interface returns a pointer directly to the
-key, and it's up to the caller to destroy the key.
+The main difference between the access points is that the in-kernel interface
+does not need to link the key to a keyring to prevent it from being immediately
+destroyed.  The kernel interface returns a pointer directly to the key, and
+it's up to the caller to destroy the key.
+
+The request_key_with_auxdata() call is like the in-kernel request_key() call,
+except that it permits auxiliary data to be passed to the upcaller (the default
+is NULL).  This is only useful for those key types that define their own upcall
+mechanism rather than using /sbin/request-key.
 
 The userspace interface links the key to a keyring associated with the process
 to prevent the key from going away, and returns the serial number of the key to
 the caller.
 
 
+The following example assumes that the key types involved don't define their
+own upcall mechanisms.  If they do, then those should be substituted for the
+forking and execution of /sbin/request-key.
+
+
 ===========
 THE PROCESS
 ===========
@@ -40,8 +57,8 @@ A request proceeds in the following manner:
      interface].
 
  (2) request_key() searches the process's subscribed keyrings to see if there's
-     a suitable key there. If there is, it returns the key. If there isn't, and
-     callout_info is not set, an error is returned. Otherwise the process
+     a suitable key there.  If there is, it returns the key.  If there isn't,
+     and callout_info is not set, an error is returned.  Otherwise the process
      proceeds to the next step.
 
  (3) request_key() sees that A doesn't have the desired key yet, so it creates
@@ -62,7 +79,7 @@ A request proceeds in the following manner:
      instantiation.
 
  (7) The program may want to access another key from A's context (say a
-     Kerberos TGT key). It just requests the appropriate key, and the keyring
+     Kerberos TGT key).  It just requests the appropriate key, and the keyring
      search notes that the session keyring has auth key V in its bottom level.
 
      This will permit it to then search the keyrings of process A with the
@@ -79,10 +96,11 @@ A request proceeds in the following manner:
 (10) The program then exits 0 and request_key() deletes key V and returns key
      U to the caller.
 
-This also extends further. If key W (step 7 above) didn't exist, key W would be
-created uninstantiated, another auth key (X) would be created (as per step 3)
-and another copy of /sbin/request-key spawned (as per step 4); but the context
-specified by auth key X will still be process A, as it was in auth key V.
+This also extends further.  If key W (step 7 above) didn't exist, key W would
+be created uninstantiated, another auth key (X) would be created (as per step
+3) and another copy of /sbin/request-key spawned (as per step 4); but the
+context specified by auth key X will still be process A, as it was in auth key
+V.
 
 This is because process A's keyrings can't simply be attached to
 /sbin/request-key at the appropriate places because (a) execve will discard two
@@ -118,17 +136,17 @@ A search of any particular keyring proceeds in the following fashion:
 
  (2) It considers all the non-keyring keys within that keyring and, if any key
      matches the criteria specified, calls key_permission(SEARCH) on it to see
-     if the key is allowed to be found. If it is, that key is returned; if
+     if the key is allowed to be found.  If it is, that key is returned; if
      not, the search continues, and the error code is retained if of higher
      priority than the one currently set.
 
  (3) It then considers all the keyring-type keys in the keyring it's currently
-     searching. It calls key_permission(SEARCH) on each keyring, and if this
+     searching.  It calls key_permission(SEARCH) on each keyring, and if this
      grants permission, it recurses, executing steps (2) and (3) on that
      keyring.
 
 The process stops immediately a valid key is found with permission granted to
-use it. Any error from a previous match attempt is discarded and the key is
+use it.  Any error from a previous match attempt is discarded and the key is
 returned.
 
 When search_process_keyrings() is invoked, it performs the following searches
@@ -153,7 +171,7 @@ The moment one succeeds, all pending errors are discarded and the found key is
 returned.
 
 Only if all these fail does the whole thing fail with the highest priority
-error. Note that several errors may have come from LSM.
+error.  Note that several errors may have come from LSM.
 
 The error priority is:
 
diff --git a/Documentation/keys.txt b/Documentation/keys.txt
index 61c0fad2fe2f..e373f0212843 100644
--- a/Documentation/keys.txt
+++ b/Documentation/keys.txt
@@ -780,6 +780,17 @@ payload contents" for more information.
     See also Documentation/keys-request-key.txt.
 
 
+(*) To search for a key, passing auxiliary data to the upcaller, call:
+
+        struct key *request_key_with_auxdata(const struct key_type *type,
+                                             const char *description,
+                                             const char *callout_string,
+                                             void *aux);
+
+    This is identical to request_key(), except that the auxiliary data is
+    passed to the key_type->request_key() op if it exists.
+
+
 (*) When it is no longer required, the key should be released using:
 
         void key_put(struct key *key);
@@ -1031,6 +1042,24 @@ The structure has a number of fields, some of which are mandatory:
      as might happen when the userspace buffer is accessed.
 
 
+ (*) int (*request_key)(struct key *key, struct key *authkey, const char *op,
+                        void *aux);
+
+     This method is optional.  If provided, request_key() and
+     request_key_with_auxdata() will invoke this function rather than
+     upcalling to /sbin/request-key to operate upon a key of this type.
+
+     The aux parameter is as passed to request_key_with_auxdata() or is NULL
+     otherwise.  Also passed are the key to be operated upon, the
+     authorisation key for this operation and the operation type (currently
+     only "create").
+
+     This function should return only when the upcall is complete.  Upon return
+     the authorisation key will be revoked, and the target key will be
+     negatively instantiated if it is still uninstantiated.  The error will be
+     returned to the caller of request_key*().
+
+
 ============================
 REQUEST-KEY CALLBACK SERVICE
 ============================