- ===================
- 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,
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,
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,
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.
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
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
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.
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.
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
git.samba.org / sfrench / cifs-2.6.git / commitdiff