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Commit 3db38ed7 authored by Kees Cook's avatar Kees Cook Committed by Jonathan Corbet
Browse files

doc: ReSTify keys-request-key.txt 



Adjusts for ReST markup and moves under keys security devel index.

Cc: David Howells <dhowells@redhat.com>
Signed-off-by: default avatarKees Cook <keescook@chromium.org>
Signed-off-by: default avatarJonathan Corbet <corbet@lwn.net>
parent 09f5412c

Documentation/filesystems/nfs/idmapper.txt

+1 −1
Original line number Diff line number Diff line
@@ -55,7 +55,7 @@ request-key will find the first matching line and corresponding program. In 
this case, /some/other/program will handle all uid lookups and

/usr/sbin/nfs.idmap will handle gid, user, and group lookups.



See <file:Documentation/security/keys-request-key.txt> for more information

See <file:Documentation/security/keys/request-key.rst> for more information

about the request-key function.

Documentation/networking/dns_resolver.txt

+1 −1
Original line number Diff line number Diff line
@@ -143,7 +143,7 @@ the key will be discarded and recreated when the data it holds has expired. 
dns_query() returns a copy of the value attached to the key, or an error if

that is indicated instead.



See <file:Documentation/security/keys-request-key.txt> for further

See <file:Documentation/security/keys/request-key.rst> for further

information about request-key function.

Documentation/security/00-INDEX

+0 −2
Original line number Diff line number Diff line 
00-INDEX

	- this file.

keys-request-key.txt

	- description of the kernel key request service.

keys-trusted-encrypted.txt

	- info on the Trusted and Encrypted keys in the kernel key ring service.

Documentation/security/keys/index.rst

+1 −0
Original line number Diff line number Diff line
@@ -7,3 +7,4 @@ Kernel Keys 


   core

   ecryptfs

   request-key

Documentation/security/keys-request-key.txt→Documentation/security/keys/request-key.rst

+33 −36
Original line number Diff line number Diff line 
===================

			      KEY REQUEST SERVICE

Key Request Service

===================



The key request service is part of the key retention service (refer to
@@ -7,13 +7,13 @@ Documentation/security/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_info);



or:

or::



	struct key *request_key_with_auxdata(const struct key_type *type,

					     const char *description,
@@ -21,14 +21,14 @@ or: 
					     size_t callout_len,

					     void *aux);



or:

or::



	struct key *request_key_async(const struct key_type *type,

				      const char *description,

				      const char *callout_info,

				      size_t callout_len);



or:

or::



	struct key *request_key_async_with_auxdata(const struct key_type *type,

						   const char *description,
@@ -36,7 +36,7 @@ or: 
					     	   size_t callout_len,

						   void *aux);



Or by userspace invoking the request_key system call:

Or by userspace invoking the request_key system call::



	key_serial_t request_key(const char *type,

				 const char *description,
@@ -67,38 +67,37 @@ own upcall mechanisms. If they do, then those should be substituted for the 
forking and execution of /sbin/request-key.





===========

THE PROCESS

The Process

===========



A request proceeds in the following manner:



 (1) Process A calls request_key() [the userspace syscall calls the kernel

  1) Process A calls request_key() [the userspace syscall calls the kernel

     interface].



 (2) request_key() searches the process's subscribed keyrings to see if there's

  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

     proceeds to the next step.



 (3) request_key() sees that A doesn't have the desired key yet, so it creates

  3) request_key() sees that A doesn't have the desired key yet, so it creates

     two things:



     (a) An uninstantiated key U of requested type and description.

      a) An uninstantiated key U of requested type and description.



     (b) An authorisation key V that refers to key U and notes that process A

      b) An authorisation key V that refers to key U and notes that process A

     	 is the context in which key U should be instantiated and secured, and

     	 from which associated key requests may be satisfied.



 (4) request_key() then forks and executes /sbin/request-key with a new session

  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 assumes the authority associated with key U.

  5) /sbin/request-key assumes the authority associated with key U.



 (6) /sbin/request-key execs an appropriate program to perform the actual

  6) /sbin/request-key execs an appropriate program to perform the actual

     instantiation.



 (7) 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.
@@ -110,10 +109,10 @@ A request proceeds in the following manner: 
     instantiate key U, using key W as a reference (perhaps it contacts a

     Kerberos server using the TGT) and then instantiates key U.



 (9) 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.



(10) 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 7 above) didn't exist, key W would
@@ -127,8 +126,7 @@ This is because process A's keyrings can't simply be attached to 
of them, and (b) it requires the same UID/GID/Groups all the way through.





====================================

NEGATIVE INSTANTIATION AND REJECTION

Negative Instantiation And Rejection

====================================



Rather than instantiating a key, it is possible for the possessor of an
@@ -145,23 +143,22 @@ signal, the key under construction will be automatically negatively 
instantiated for a short amount of time.





====================

THE SEARCH ALGORITHM

The Search Algorithm

====================



A search of any particular keyring proceeds in the following fashion:



 (1) When the key management code searches for a key (keyring_search_aux) it

  1) When the key management code searches for a key (keyring_search_aux) it

     firstly calls key_permission(SEARCH) on the keyring it's starting with,

     if this denies permission, it doesn't search further.



 (2) It considers all the non-keyring keys within that keyring and, if any key

  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

     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

  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

     grants permission, it recurses, executing steps (2) and (3) on that

     keyring.
@@ -173,20 +170,20 @@ returned. 
When search_process_keyrings() is invoked, it performs the following searches

until one succeeds:



 (1) If extant, the process's thread keyring is searched.

  1) If extant, the process's thread keyring is searched.



 (2) If extant, the process's process keyring is searched.

  2) If extant, the process's process keyring is searched.



 (3) The process's session keyring is searched.

  3) The process's session keyring is searched.



 (4) If the process has assumed the authority associated with a request_key()

  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.

      a) If extant, the calling process's thread keyring is searched.



     (b) If extant, the calling process's process keyring is searched.

      b) If extant, the calling process's process keyring is searched.



     (c) The calling process's session keyring is searched.

      c) The calling process's session keyring is searched.



The moment one succeeds, all pending errors are discarded and the found key is

returned.
@@ -194,7 +191,7 @@ 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.



The error priority is:

The error priority is::



	EKEYREVOKED > EKEYEXPIRED > ENOKEY