linux/security/keys/request_key.c
David Howells 3e30148c3d [PATCH] Keys: Make request-key create an authorisation key
The attached patch makes the following changes:

 (1) There's a new special key type called ".request_key_auth".

     This is an authorisation key for when one process requests a key and
     another process is started to construct it. This type of key cannot be
     created by the user; nor can it be requested by kernel services.

     Authorisation keys hold two references:

     (a) Each refers to a key being constructed. When the key being
     	 constructed is instantiated the authorisation key is revoked,
     	 rendering it of no further use.

     (b) The "authorising process". This is either:

     	 (i) the process that called request_key(), or:

     	 (ii) if the process that called request_key() itself had an
     	      authorisation key in its session keyring, then the authorising
     	      process referred to by that authorisation key will also be
     	      referred to by the new authorisation key.

	 This means that the process that initiated a chain of key requests
	 will authorise the lot of them, and will, by default, wind up with
	 the keys obtained from them in its keyrings.

 (2) request_key() creates an authorisation key which is then passed to
     /sbin/request-key in as part of a new session keyring.

 (3) When request_key() is searching for a key to hand back to the caller, if
     it comes across an authorisation key in the session keyring of the
     calling process, it will also search the keyrings of the process
     specified therein and it will use the specified process's credentials
     (fsuid, fsgid, groups) to do that rather than the calling process's
     credentials.

     This allows a process started by /sbin/request-key to find keys belonging
     to the authorising process.

 (4) A key can be read, even if the process executing KEYCTL_READ doesn't have
     direct read or search permission if that key is contained within the
     keyrings of a process specified by an authorisation key found within the
     calling process's session keyring, and is searchable using the
     credentials of the authorising process.

     This allows a process started by /sbin/request-key to read keys belonging
     to the authorising process.

 (5) The magic KEY_SPEC_*_KEYRING key IDs when passed to KEYCTL_INSTANTIATE or
     KEYCTL_NEGATE will specify a keyring of the authorising process, rather
     than the process doing the instantiation.

 (6) One of the process keyrings can be nominated as the default to which
     request_key() should attach new keys if not otherwise specified. This is
     done with KEYCTL_SET_REQKEY_KEYRING and one of the KEY_REQKEY_DEFL_*
     constants. The current setting can also be read using this call.

 (7) request_key() is partially interruptible. If it is waiting for another
     process to finish constructing a key, it can be interrupted. This permits
     a request-key cycle to be broken without recourse to rebooting.

Signed-Off-By: David Howells <dhowells@redhat.com>
Signed-Off-By: Benoit Boissinot <benoit.boissinot@ens-lyon.org>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>
2005-06-24 00:05:19 -07:00

475 lines
12 KiB
C

/* request_key.c: request a key from userspace
*
* Copyright (C) 2004-5 Red Hat, Inc. All Rights Reserved.
* Written by David Howells (dhowells@redhat.com)
*
* This program is free software; you can redistribute it and/or
* modify it under the terms of the GNU General Public License
* as published by the Free Software Foundation; either version
* 2 of the License, or (at your option) any later version.
*/
#include <linux/module.h>
#include <linux/sched.h>
#include <linux/kmod.h>
#include <linux/err.h>
#include <linux/keyctl.h>
#include "internal.h"
struct key_construction {
struct list_head link; /* link in construction queue */
struct key *key; /* key being constructed */
};
/* when waiting for someone else's keys, you get added to this */
DECLARE_WAIT_QUEUE_HEAD(request_key_conswq);
/*****************************************************************************/
/*
* request userspace finish the construction of a key
* - execute "/sbin/request-key <op> <key> <uid> <gid> <keyring> <keyring> <keyring> <info>"
*/
static int call_request_key(struct key *key,
const char *op,
const char *callout_info)
{
struct task_struct *tsk = current;
key_serial_t prkey, sskey;
struct key *session_keyring, *rkakey;
char *argv[10], *envp[3], uid_str[12], gid_str[12];
char key_str[12], keyring_str[3][12];
int ret, i;
kenter("{%d},%s,%s", key->serial, op, callout_info);
/* generate a new session keyring with an auth key in it */
session_keyring = request_key_auth_new(key, &rkakey);
if (IS_ERR(session_keyring)) {
ret = PTR_ERR(session_keyring);
goto error;
}
/* record the UID and GID */
sprintf(uid_str, "%d", current->fsuid);
sprintf(gid_str, "%d", current->fsgid);
/* we say which key is under construction */
sprintf(key_str, "%d", key->serial);
/* we specify the process's default keyrings */
sprintf(keyring_str[0], "%d",
tsk->thread_keyring ? tsk->thread_keyring->serial : 0);
prkey = 0;
if (tsk->signal->process_keyring)
prkey = tsk->signal->process_keyring->serial;
sprintf(keyring_str[1], "%d", prkey);
if (tsk->signal->session_keyring) {
rcu_read_lock();
sskey = rcu_dereference(tsk->signal->session_keyring)->serial;
rcu_read_unlock();
}
else {
sskey = tsk->user->session_keyring->serial;
}
sprintf(keyring_str[2], "%d", sskey);
/* set up a minimal environment */
i = 0;
envp[i++] = "HOME=/";
envp[i++] = "PATH=/sbin:/bin:/usr/sbin:/usr/bin";
envp[i] = NULL;
/* set up the argument list */
i = 0;
argv[i++] = "/sbin/request-key";
argv[i++] = (char *) op;
argv[i++] = key_str;
argv[i++] = uid_str;
argv[i++] = gid_str;
argv[i++] = keyring_str[0];
argv[i++] = keyring_str[1];
argv[i++] = keyring_str[2];
argv[i++] = (char *) callout_info;
argv[i] = NULL;
/* do it */
ret = call_usermodehelper_keys(argv[0], argv, envp, session_keyring, 1);
/* dispose of the special keys */
key_revoke(rkakey);
key_put(rkakey);
key_put(session_keyring);
error:
kleave(" = %d", ret);
return ret;
} /* end call_request_key() */
/*****************************************************************************/
/*
* call out to userspace for the key
* - called with the construction sem held, but the sem is dropped here
* - we ignore program failure and go on key status instead
*/
static struct key *__request_key_construction(struct key_type *type,
const char *description,
const char *callout_info)
{
struct key_construction cons;
struct timespec now;
struct key *key;
int ret, negated;
kenter("%s,%s,%s", type->name, description, callout_info);
/* create a key and add it to the queue */
key = key_alloc(type, description,
current->fsuid, current->fsgid, KEY_USR_ALL, 0);
if (IS_ERR(key))
goto alloc_failed;
set_bit(KEY_FLAG_USER_CONSTRUCT, &key->flags);
cons.key = key;
list_add_tail(&cons.link, &key->user->consq);
/* we drop the construction sem here on behalf of the caller */
up_write(&key_construction_sem);
/* make the call */
ret = call_request_key(key, "create", callout_info);
if (ret < 0)
goto request_failed;
/* if the key wasn't instantiated, then we want to give an error */
ret = -ENOKEY;
if (!test_bit(KEY_FLAG_INSTANTIATED, &key->flags))
goto request_failed;
down_write(&key_construction_sem);
list_del(&cons.link);
up_write(&key_construction_sem);
/* also give an error if the key was negatively instantiated */
check_not_negative:
if (test_bit(KEY_FLAG_NEGATIVE, &key->flags)) {
key_put(key);
key = ERR_PTR(-ENOKEY);
}
out:
kleave(" = %p", key);
return key;
request_failed:
/* it wasn't instantiated
* - remove from construction queue
* - mark the key as dead
*/
negated = 0;
down_write(&key_construction_sem);
list_del(&cons.link);
/* check it didn't get instantiated between the check and the down */
if (!test_bit(KEY_FLAG_INSTANTIATED, &key->flags)) {
set_bit(KEY_FLAG_NEGATIVE, &key->flags);
set_bit(KEY_FLAG_INSTANTIATED, &key->flags);
negated = 1;
}
clear_bit(KEY_FLAG_USER_CONSTRUCT, &key->flags);
up_write(&key_construction_sem);
if (!negated)
goto check_not_negative; /* surprisingly, the key got
* instantiated */
/* set the timeout and store in the session keyring if we can */
now = current_kernel_time();
key->expiry = now.tv_sec + key_negative_timeout;
if (current->signal->session_keyring) {
struct key *keyring;
rcu_read_lock();
keyring = rcu_dereference(current->signal->session_keyring);
atomic_inc(&keyring->usage);
rcu_read_unlock();
key_link(keyring, key);
key_put(keyring);
}
key_put(key);
/* notify anyone who was waiting */
wake_up_all(&request_key_conswq);
key = ERR_PTR(ret);
goto out;
alloc_failed:
up_write(&key_construction_sem);
goto out;
} /* end __request_key_construction() */
/*****************************************************************************/
/*
* call out to userspace to request the key
* - we check the construction queue first to see if an appropriate key is
* already being constructed by userspace
*/
static struct key *request_key_construction(struct key_type *type,
const char *description,
struct key_user *user,
const char *callout_info)
{
struct key_construction *pcons;
struct key *key, *ckey;
DECLARE_WAITQUEUE(myself, current);
kenter("%s,%s,{%d},%s",
type->name, description, user->uid, callout_info);
/* see if there's such a key under construction already */
down_write(&key_construction_sem);
list_for_each_entry(pcons, &user->consq, link) {
ckey = pcons->key;
if (ckey->type != type)
continue;
if (type->match(ckey, description))
goto found_key_under_construction;
}
/* see about getting userspace to construct the key */
key = __request_key_construction(type, description, callout_info);
error:
kleave(" = %p", key);
return key;
/* someone else has the same key under construction
* - we want to keep an eye on their key
*/
found_key_under_construction:
atomic_inc(&ckey->usage);
up_write(&key_construction_sem);
/* wait for the key to be completed one way or another */
add_wait_queue(&request_key_conswq, &myself);
for (;;) {
set_current_state(TASK_INTERRUPTIBLE);
if (!test_bit(KEY_FLAG_USER_CONSTRUCT, &ckey->flags))
break;
if (signal_pending(current))
break;
schedule();
}
set_current_state(TASK_RUNNING);
remove_wait_queue(&request_key_conswq, &myself);
/* we'll need to search this process's keyrings to see if the key is
* now there since we can't automatically assume it's also available
* there */
key_put(ckey);
ckey = NULL;
key = NULL; /* request a retry */
goto error;
} /* end request_key_construction() */
/*****************************************************************************/
/*
* link a freshly minted key to an appropriate destination keyring
*/
static void request_key_link(struct key *key, struct key *dest_keyring)
{
struct task_struct *tsk = current;
struct key *drop = NULL;
kenter("{%d},%p", key->serial, dest_keyring);
/* find the appropriate keyring */
if (!dest_keyring) {
switch (tsk->jit_keyring) {
case KEY_REQKEY_DEFL_DEFAULT:
case KEY_REQKEY_DEFL_THREAD_KEYRING:
dest_keyring = tsk->thread_keyring;
if (dest_keyring)
break;
case KEY_REQKEY_DEFL_PROCESS_KEYRING:
dest_keyring = tsk->signal->process_keyring;
if (dest_keyring)
break;
case KEY_REQKEY_DEFL_SESSION_KEYRING:
rcu_read_lock();
dest_keyring = key_get(
rcu_dereference(tsk->signal->session_keyring));
rcu_read_unlock();
drop = dest_keyring;
if (dest_keyring)
break;
case KEY_REQKEY_DEFL_USER_SESSION_KEYRING:
dest_keyring = current->user->session_keyring;
break;
case KEY_REQKEY_DEFL_USER_KEYRING:
dest_keyring = current->user->uid_keyring;
break;
case KEY_REQKEY_DEFL_GROUP_KEYRING:
default:
BUG();
}
}
/* and attach the key to it */
key_link(dest_keyring, key);
key_put(drop);
kleave("");
} /* end request_key_link() */
/*****************************************************************************/
/*
* request a key
* - search the process's keyrings
* - check the list of keys being created or updated
* - call out to userspace for a key if supplementary info was provided
* - cache the key in an appropriate keyring
*/
struct key *request_key_and_link(struct key_type *type,
const char *description,
const char *callout_info,
struct key *dest_keyring)
{
struct key_user *user;
struct key *key;
kenter("%s,%s,%s,%p",
type->name, description, callout_info, dest_keyring);
/* search all the process keyrings for a key */
key = search_process_keyrings(type, description, type->match, current);
if (PTR_ERR(key) == -EAGAIN) {
/* the search failed, but the keyrings were searchable, so we
* should consult userspace if we can */
key = ERR_PTR(-ENOKEY);
if (!callout_info)
goto error;
/* - get hold of the user's construction queue */
user = key_user_lookup(current->fsuid);
if (!user)
goto nomem;
do {
if (signal_pending(current))
goto interrupted;
/* ask userspace (returns NULL if it waited on a key
* being constructed) */
key = request_key_construction(type, description,
user, callout_info);
if (key)
break;
/* someone else made the key we want, so we need to
* search again as it might now be available to us */
key = search_process_keyrings(type, description,
type->match, current);
} while (PTR_ERR(key) == -EAGAIN);
key_user_put(user);
/* link the new key into the appropriate keyring */
if (!PTR_ERR(key))
request_key_link(key, dest_keyring);
}
error:
kleave(" = %p", key);
return key;
nomem:
key = ERR_PTR(-ENOMEM);
goto error;
interrupted:
key_user_put(user);
key = ERR_PTR(-EINTR);
goto error;
} /* end request_key_and_link() */
/*****************************************************************************/
/*
* request a key
* - search the process's keyrings
* - check the list of keys being created or updated
* - call out to userspace for a key if supplementary info was provided
*/
struct key *request_key(struct key_type *type,
const char *description,
const char *callout_info)
{
return request_key_and_link(type, description, callout_info, NULL);
} /* end request_key() */
EXPORT_SYMBOL(request_key);
/*****************************************************************************/
/*
* validate a key
*/
int key_validate(struct key *key)
{
struct timespec now;
int ret = 0;
if (key) {
/* check it's still accessible */
ret = -EKEYREVOKED;
if (test_bit(KEY_FLAG_REVOKED, &key->flags) ||
test_bit(KEY_FLAG_DEAD, &key->flags))
goto error;
/* check it hasn't expired */
ret = 0;
if (key->expiry) {
now = current_kernel_time();
if (now.tv_sec >= key->expiry)
ret = -EKEYEXPIRED;
}
}
error:
return ret;
} /* end key_validate() */
EXPORT_SYMBOL(key_validate);