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doc: ReSTify keys-request-key.txt

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

Cc: David Howells <dhowells@redhat.com>
Signed-off-by: Kees Cook <keescook@chromium.org>
Signed-off-by: Jonathan Corbet <corbet@lwn.net>
This commit is contained in:
Kees Cook 2017-05-13 04:51:52 -07:00 committed by Jonathan Corbet
parent 09f5412cc5
commit 3db38ed768
7 changed files with 38 additions and 42 deletions
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2
Documentation/filesystems/nfs/idmapper.txt
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@ -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.

2
Documentation/networking/dns_resolver.txt
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@ -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.

2
Documentation/security/00-INDEX
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@ -1,6 +1,4 @@
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.

1
Documentation/security/keys/index.rst
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@ -7,3 +7,4 @@ Kernel Keys
core
ecryptfs
request-key

69
Documentation/security/keys-request-key.txt → Documentation/security/keys/request-key.rst
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@ -1,19 +1,19 @@
===================
KEY REQUEST SERVICE
===================
===================
Key Request Service
===================
The key request service is part of the key retention service (refer to
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

2
security/keys/request_key.c
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@ -8,7 +8,7 @@
* as published by the Free Software Foundation; either version
* 2 of the License, or (at your option) any later version.
*
* See Documentation/security/keys-request-key.txt
* See Documentation/security/keys/request-key.rst
*/
#include <linux/module.h>

2
security/keys/request_key_auth.c
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@ -8,7 +8,7 @@
* as published by the Free Software Foundation; either version
* 2 of the License, or (at your option) any later version.
*
* See Documentation/security/keys-request-key.txt
* See Documentation/security/keys/request-key.rst
*/
#include <linux/module.h>