[PATCH] keys: Permit running process to instantiate keys

Make it possible for a running process (such as gssapid) to be able to
instantiate a key, as was requested by Trond Myklebust for NFS4.

The patch makes the following changes:

 (1) A new, optional key type method has been added. This permits a key type
     to intercept requests at the point /sbin/request-key is about to be
     spawned and do something else with them - passing them over the
     rpc_pipefs files or netlink sockets for instance.

     The uninstantiated key, the authorisation key and the intended operation
     name are passed to the method.

 (2) The callout_info is no longer passed as an argument to /sbin/request-key
     to prevent unauthorised viewing of this data using ps or by looking in
     /proc/pid/cmdline.

     This means that the old /sbin/request-key program will not work with the
     patched kernel as it will expect to see an extra argument that is no
     longer there.

     A revised keyutils package will be made available tomorrow.

 (3) The callout_info is now attached to the authorisation key. Reading this
     key will retrieve the information.

 (4) A new field has been added to the task_struct. This holds the
     authorisation key currently active for a thread. Searches now look here
     for the caller's set of keys rather than looking for an auth key in the
     lowest level of the session keyring.

     This permits a thread to be servicing multiple requests at once and to
     switch between them. Note that this is per-thread, not per-process, and
     so is usable in multithreaded programs.

     The setting of this field is inherited across fork and exec.

 (5) A new keyctl function (KEYCTL_ASSUME_AUTHORITY) has been added that
     permits a thread to assume the authority to deal with an uninstantiated
     key. Assumption is only permitted if the authorisation key associated
     with the uninstantiated key is somewhere in the thread's keyrings.

     This function can also clear the assumption.

 (6) A new magic key specifier has been added to refer to the currently
     assumed authorisation key (KEY_SPEC_REQKEY_AUTH_KEY).

 (7) Instantiation will only proceed if the appropriate authorisation key is
     assumed first. The assumed authorisation key is discarded if
     instantiation is successful.

 (8) key_validate() is moved from the file of request_key functions to the
     file of permissions functions.

 (9) The documentation is updated.

From: <Valdis.Kletnieks@vt.edu>

    Build fix.

Signed-off-by: David Howells <dhowells@redhat.com>
Cc: Trond Myklebust <trond.myklebust@fys.uio.no>
Cc: Alexander Zangerl <az@bond.edu.au>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>

2 files changed, 36 insertions, 10 deletions

diff --git a/Documentation/keys-request-key.txt b/Documentation/keys-request-key.txt
index 5f2b9c5edbb..22488d79116 100644
--- a/Documentation/keys-request-key.txt
+++ b/Documentation/keys-request-key.txt
@@ -56,10 +56,12 @@ A request proceeds in the following manner:
  (4) request_key() then forks and executes /sbin/request-key with a new session
      keyring that contains a link to auth key V.
 
- (5) /sbin/request-key execs an appropriate program to perform the actual
+ (5) /sbin/request-key assumes the authority associated with key U.
+
+ (6) /sbin/request-key execs an appropriate program to perform the actual
      instantiation.
 
- (6) The program may want to access another key from A's context (say a
+ (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
      search notes that the session keyring has auth key V in its bottom level.
 
@@ -67,19 +69,19 @@ A request proceeds in the following manner:
      UID, GID, groups and security info of process A as if it was process A,
      and come up with key W.
 
- (7) The program then does what it must to get the data with which to
+ (8) The program then does what it must to get the data with which to
      instantiate key U, using key W as a reference (perhaps it contacts a
      Kerberos server using the TGT) and then instantiates key U.
 
- (8) Upon instantiating key U, auth key V is automatically revoked so that it
+ (9) Upon instantiating key U, auth key V is automatically revoked so that it
      may not be used again.
 
- (9) The program then exits 0 and request_key() deletes key V and returns key
+(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 5 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
+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
@@ -138,8 +140,8 @@ until one succeeds:
 
  (3) The process's session keyring is searched.
 
- (4) If the process has a request_key() authorisation key in its session
-     keyring then:
+ (4) If the process has assumed the authority associated with a request_key()
+     authorisation key then:
 
      (a) If extant, the calling process's thread keyring is searched.
 
diff --git a/Documentation/keys.txt b/Documentation/keys.txt
index eeda00f82d2..aaa01b0e3ee 100644
--- a/Documentation/keys.txt
+++ b/Documentation/keys.txt
@@ -308,6 +308,8 @@ process making the call:
 	KEY_SPEC_USER_KEYRING		-4	UID-specific keyring
 	KEY_SPEC_USER_SESSION_KEYRING	-5	UID-session keyring
 	KEY_SPEC_GROUP_KEYRING		-6	GID-specific keyring
+	KEY_SPEC_REQKEY_AUTH_KEY	-7	assumed request_key()
+						  authorisation key
 
 
 The main syscalls are:
@@ -645,6 +647,28 @@ The keyctl syscall functions are:
      or expired keys.
 
 
+ (*) Assume the authority granted to instantiate a key
+
+	long keyctl(KEYCTL_ASSUME_AUTHORITY, key_serial_t key);
+
+     This assumes or divests the authority required to instantiate the
+     specified key. Authority can only be assumed if the thread has the
+     authorisation key associated with the specified key in its keyrings
+     somewhere.
+
+     Once authority is assumed, searches for keys will also search the
+     requester's keyrings using the requester's security label, UID, GID and
+     groups.
+
+     If the requested authority is unavailable, error EPERM will be returned,
+     likewise if the authority has been revoked because the target key is
+     already instantiated.
+
+     If the specified key is 0, then any assumed authority will be divested.
+
+     The assumed authorititive key is inherited across fork and exec.
+
+
 ===============
 KERNEL SERVICES
 ===============