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![David Howells](/assets/img/avatar_default.png)
The attached patch changes the key implementation in a number of ways: (1) It removes the spinlock from the key structure. (2) The key flags are now accessed using atomic bitops instead of write-locking the key spinlock and using C bitwise operators. The three instantiation flags are dealt with with the construction semaphore held during the request_key/instantiate/negate sequence, thus rendering the spinlock superfluous. The key flags are also now bit numbers not bit masks. (3) The key payload is now accessed using RCU. This permits the recursive keyring search algorithm to be simplified greatly since no locks need be taken other than the usual RCU preemption disablement. Searching now does not require any locks or semaphores to be held; merely that the starting keyring be pinned. (4) The keyring payload now includes an RCU head so that it can be disposed of by call_rcu(). This requires that the payload be copied on unlink to prevent introducing races in copy-down vs search-up. (5) The user key payload is now a structure with the data following it. It includes an RCU head like the keyring payload and for the same reason. It also contains a data length because the data length in the key may be changed on another CPU whilst an RCU protected read is in progress on the payload. This would then see the supposed RCU payload and the on-key data length getting out of sync. I'm tempted to drop the key's datalen entirely, except that it's used in conjunction with quota management and so is a little tricky to get rid of. (6) Update the keys documentation. Signed-Off-By: David Howells <dhowells@redhat.com> Signed-off-by: Andrew Morton <akpm@osdl.org> Signed-off-by: Linus Torvalds <torvalds@osdl.org>
357 lines
9.1 KiB
C
357 lines
9.1 KiB
C
/* request_key.c: request a key from userspace
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*
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* Copyright (C) 2004 Red Hat, Inc. All Rights Reserved.
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* Written by David Howells (dhowells@redhat.com)
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*
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* This program is free software; you can redistribute it and/or
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* modify it under the terms of the GNU General Public License
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* as published by the Free Software Foundation; either version
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* 2 of the License, or (at your option) any later version.
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*/
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#include <linux/module.h>
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#include <linux/sched.h>
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#include <linux/kmod.h>
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#include <linux/err.h>
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#include "internal.h"
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struct key_construction {
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struct list_head link; /* link in construction queue */
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struct key *key; /* key being constructed */
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};
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/* when waiting for someone else's keys, you get added to this */
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DECLARE_WAIT_QUEUE_HEAD(request_key_conswq);
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/*****************************************************************************/
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/*
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* request userspace finish the construction of a key
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* - execute "/sbin/request-key <op> <key> <uid> <gid> <keyring> <keyring> <keyring> <info>"
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* - if callout_info is an empty string, it'll be rendered as a "-" instead
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*/
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static int call_request_key(struct key *key,
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const char *op,
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const char *callout_info)
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{
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struct task_struct *tsk = current;
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unsigned long flags;
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key_serial_t prkey, sskey;
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char *argv[10], *envp[3], uid_str[12], gid_str[12];
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char key_str[12], keyring_str[3][12];
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int i;
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/* record the UID and GID */
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sprintf(uid_str, "%d", current->fsuid);
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sprintf(gid_str, "%d", current->fsgid);
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/* we say which key is under construction */
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sprintf(key_str, "%d", key->serial);
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/* we specify the process's default keyrings */
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sprintf(keyring_str[0], "%d",
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tsk->thread_keyring ? tsk->thread_keyring->serial : 0);
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prkey = 0;
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if (tsk->signal->process_keyring)
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prkey = tsk->signal->process_keyring->serial;
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sskey = 0;
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spin_lock_irqsave(&tsk->sighand->siglock, flags);
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if (tsk->signal->session_keyring)
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sskey = tsk->signal->session_keyring->serial;
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spin_unlock_irqrestore(&tsk->sighand->siglock, flags);
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if (!sskey)
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sskey = tsk->user->session_keyring->serial;
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sprintf(keyring_str[1], "%d", prkey);
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sprintf(keyring_str[2], "%d", sskey);
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/* set up a minimal environment */
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i = 0;
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envp[i++] = "HOME=/";
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envp[i++] = "PATH=/sbin:/bin:/usr/sbin:/usr/bin";
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envp[i] = NULL;
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/* set up the argument list */
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i = 0;
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argv[i++] = "/sbin/request-key";
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argv[i++] = (char *) op;
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argv[i++] = key_str;
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argv[i++] = uid_str;
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argv[i++] = gid_str;
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argv[i++] = keyring_str[0];
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argv[i++] = keyring_str[1];
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argv[i++] = keyring_str[2];
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argv[i++] = callout_info[0] ? (char *) callout_info : "-";
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argv[i] = NULL;
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/* do it */
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return call_usermodehelper(argv[0], argv, envp, 1);
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} /* end call_request_key() */
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/*****************************************************************************/
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/*
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* call out to userspace for the key
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* - called with the construction sem held, but the sem is dropped here
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* - we ignore program failure and go on key status instead
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*/
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static struct key *__request_key_construction(struct key_type *type,
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const char *description,
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const char *callout_info)
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{
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struct key_construction cons;
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struct timespec now;
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struct key *key;
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int ret, negated;
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/* create a key and add it to the queue */
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key = key_alloc(type, description,
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current->fsuid, current->fsgid, KEY_USR_ALL, 0);
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if (IS_ERR(key))
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goto alloc_failed;
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set_bit(KEY_FLAG_USER_CONSTRUCT, &key->flags);
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cons.key = key;
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list_add_tail(&cons.link, &key->user->consq);
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/* we drop the construction sem here on behalf of the caller */
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up_write(&key_construction_sem);
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/* make the call */
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ret = call_request_key(key, "create", callout_info);
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if (ret < 0)
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goto request_failed;
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/* if the key wasn't instantiated, then we want to give an error */
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ret = -ENOKEY;
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if (!test_bit(KEY_FLAG_INSTANTIATED, &key->flags))
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goto request_failed;
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down_write(&key_construction_sem);
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list_del(&cons.link);
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up_write(&key_construction_sem);
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/* also give an error if the key was negatively instantiated */
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check_not_negative:
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if (test_bit(KEY_FLAG_NEGATIVE, &key->flags)) {
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key_put(key);
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key = ERR_PTR(-ENOKEY);
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}
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out:
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return key;
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request_failed:
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/* it wasn't instantiated
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* - remove from construction queue
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* - mark the key as dead
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*/
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negated = 0;
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down_write(&key_construction_sem);
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list_del(&cons.link);
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/* check it didn't get instantiated between the check and the down */
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if (!test_bit(KEY_FLAG_INSTANTIATED, &key->flags)) {
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set_bit(KEY_FLAG_NEGATIVE, &key->flags);
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set_bit(KEY_FLAG_INSTANTIATED, &key->flags);
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negated = 1;
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}
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clear_bit(KEY_FLAG_USER_CONSTRUCT, &key->flags);
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up_write(&key_construction_sem);
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if (!negated)
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goto check_not_negative; /* surprisingly, the key got
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* instantiated */
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/* set the timeout and store in the session keyring if we can */
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now = current_kernel_time();
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key->expiry = now.tv_sec + key_negative_timeout;
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if (current->signal->session_keyring) {
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unsigned long flags;
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struct key *keyring;
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spin_lock_irqsave(¤t->sighand->siglock, flags);
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keyring = current->signal->session_keyring;
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atomic_inc(&keyring->usage);
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spin_unlock_irqrestore(¤t->sighand->siglock, flags);
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key_link(keyring, key);
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key_put(keyring);
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}
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key_put(key);
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/* notify anyone who was waiting */
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wake_up_all(&request_key_conswq);
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key = ERR_PTR(ret);
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goto out;
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alloc_failed:
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up_write(&key_construction_sem);
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goto out;
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} /* end __request_key_construction() */
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/*****************************************************************************/
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/*
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* call out to userspace to request the key
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* - we check the construction queue first to see if an appropriate key is
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* already being constructed by userspace
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*/
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static struct key *request_key_construction(struct key_type *type,
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const char *description,
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struct key_user *user,
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const char *callout_info)
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{
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struct key_construction *pcons;
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struct key *key, *ckey;
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DECLARE_WAITQUEUE(myself, current);
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/* see if there's such a key under construction already */
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down_write(&key_construction_sem);
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list_for_each_entry(pcons, &user->consq, link) {
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ckey = pcons->key;
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if (ckey->type != type)
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continue;
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if (type->match(ckey, description))
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goto found_key_under_construction;
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}
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/* see about getting userspace to construct the key */
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key = __request_key_construction(type, description, callout_info);
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error:
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return key;
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/* someone else has the same key under construction
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* - we want to keep an eye on their key
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*/
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found_key_under_construction:
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atomic_inc(&ckey->usage);
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up_write(&key_construction_sem);
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/* wait for the key to be completed one way or another */
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add_wait_queue(&request_key_conswq, &myself);
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for (;;) {
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set_current_state(TASK_UNINTERRUPTIBLE);
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if (!test_bit(KEY_FLAG_USER_CONSTRUCT, &ckey->flags))
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break;
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schedule();
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}
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set_current_state(TASK_RUNNING);
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remove_wait_queue(&request_key_conswq, &myself);
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/* we'll need to search this process's keyrings to see if the key is
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* now there since we can't automatically assume it's also available
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* there */
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key_put(ckey);
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ckey = NULL;
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key = NULL; /* request a retry */
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goto error;
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} /* end request_key_construction() */
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/*****************************************************************************/
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/*
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* request a key
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* - search the process's keyrings
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* - check the list of keys being created or updated
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* - call out to userspace for a key if requested (supplementary info can be
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* passed)
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*/
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struct key *request_key(struct key_type *type,
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const char *description,
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const char *callout_info)
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{
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struct key_user *user;
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struct key *key;
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/* search all the process keyrings for a key */
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key = search_process_keyrings_aux(type, description, type->match);
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if (PTR_ERR(key) == -EAGAIN) {
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/* the search failed, but the keyrings were searchable, so we
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* should consult userspace if we can */
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key = ERR_PTR(-ENOKEY);
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if (!callout_info)
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goto error;
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/* - get hold of the user's construction queue */
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user = key_user_lookup(current->fsuid);
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if (!user) {
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key = ERR_PTR(-ENOMEM);
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goto error;
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}
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for (;;) {
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/* ask userspace (returns NULL if it waited on a key
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* being constructed) */
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key = request_key_construction(type, description,
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user, callout_info);
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if (key)
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break;
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/* someone else made the key we want, so we need to
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* search again as it might now be available to us */
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key = search_process_keyrings_aux(type, description,
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type->match);
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if (PTR_ERR(key) != -EAGAIN)
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break;
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}
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key_user_put(user);
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}
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error:
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return key;
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} /* end request_key() */
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EXPORT_SYMBOL(request_key);
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/*****************************************************************************/
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/*
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* validate a key
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*/
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int key_validate(struct key *key)
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{
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struct timespec now;
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int ret = 0;
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if (key) {
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/* check it's still accessible */
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ret = -EKEYREVOKED;
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if (test_bit(KEY_FLAG_REVOKED, &key->flags) ||
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test_bit(KEY_FLAG_DEAD, &key->flags))
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goto error;
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/* check it hasn't expired */
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ret = 0;
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if (key->expiry) {
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now = current_kernel_time();
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if (now.tv_sec >= key->expiry)
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ret = -EKEYEXPIRED;
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}
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}
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error:
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return ret;
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} /* end key_validate() */
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EXPORT_SYMBOL(key_validate);
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