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![David Howells](/assets/img/avatar_default.png)
Consolidate KEY_FLAG_INSTANTIATED, KEY_FLAG_NEGATIVE and the rejection
error into one field such that:
(1) The instantiation state can be modified/read atomically.
(2) The error can be accessed atomically with the state.
(3) The error isn't stored unioned with the payload pointers.
This deals with the problem that the state is spread over three different
objects (two bits and a separate variable) and reading or updating them
atomically isn't practical, given that not only can uninstantiated keys
change into instantiated or rejected keys, but rejected keys can also turn
into instantiated keys - and someone accessing the key might not be using
any locking.
The main side effect of this problem is that what was held in the payload
may change, depending on the state. For instance, you might observe the
key to be in the rejected state. You then read the cached error, but if
the key semaphore wasn't locked, the key might've become instantiated
between the two reads - and you might now have something in hand that isn't
actually an error code.
The state is now KEY_IS_UNINSTANTIATED, KEY_IS_POSITIVE or a negative error
code if the key is negatively instantiated. The key_is_instantiated()
function is replaced with key_is_positive() to avoid confusion as negative
keys are also 'instantiated'.
Additionally, barriering is included:
(1) Order payload-set before state-set during instantiation.
(2) Order state-read before payload-read when using the key.
Further separate barriering is necessary if RCU is being used to access the
payload content after reading the payload pointers.
Fixes: 146aa8b145
("KEYS: Merge the type-specific data with the payload data")
Cc: stable@vger.kernel.org # v4.4+
Reported-by: Eric Biggers <ebiggers@google.com>
Signed-off-by: David Howells <dhowells@redhat.com>
Reviewed-by: Eric Biggers <ebiggers@google.com>
268 lines
6.8 KiB
C
268 lines
6.8 KiB
C
/* Request key authorisation token key definition.
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*
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* Copyright (C) 2005 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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* See Documentation/security/keys/request-key.rst
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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/err.h>
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#include <linux/seq_file.h>
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#include <linux/slab.h>
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#include <linux/uaccess.h>
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#include "internal.h"
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#include <keys/user-type.h>
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static int request_key_auth_preparse(struct key_preparsed_payload *);
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static void request_key_auth_free_preparse(struct key_preparsed_payload *);
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static int request_key_auth_instantiate(struct key *,
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struct key_preparsed_payload *);
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static void request_key_auth_describe(const struct key *, struct seq_file *);
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static void request_key_auth_revoke(struct key *);
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static void request_key_auth_destroy(struct key *);
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static long request_key_auth_read(const struct key *, char __user *, size_t);
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/*
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* The request-key authorisation key type definition.
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*/
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struct key_type key_type_request_key_auth = {
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.name = ".request_key_auth",
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.def_datalen = sizeof(struct request_key_auth),
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.preparse = request_key_auth_preparse,
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.free_preparse = request_key_auth_free_preparse,
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.instantiate = request_key_auth_instantiate,
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.describe = request_key_auth_describe,
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.revoke = request_key_auth_revoke,
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.destroy = request_key_auth_destroy,
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.read = request_key_auth_read,
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};
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static int request_key_auth_preparse(struct key_preparsed_payload *prep)
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{
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return 0;
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}
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static void request_key_auth_free_preparse(struct key_preparsed_payload *prep)
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{
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}
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/*
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* Instantiate a request-key authorisation key.
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*/
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static int request_key_auth_instantiate(struct key *key,
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struct key_preparsed_payload *prep)
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{
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key->payload.data[0] = (struct request_key_auth *)prep->data;
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return 0;
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}
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/*
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* Describe an authorisation token.
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*/
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static void request_key_auth_describe(const struct key *key,
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struct seq_file *m)
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{
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struct request_key_auth *rka = key->payload.data[0];
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seq_puts(m, "key:");
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seq_puts(m, key->description);
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if (key_is_positive(key))
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seq_printf(m, " pid:%d ci:%zu", rka->pid, rka->callout_len);
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}
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/*
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* Read the callout_info data (retrieves the callout information).
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* - the key's semaphore is read-locked
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*/
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static long request_key_auth_read(const struct key *key,
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char __user *buffer, size_t buflen)
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{
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struct request_key_auth *rka = key->payload.data[0];
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size_t datalen;
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long ret;
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datalen = rka->callout_len;
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ret = datalen;
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/* we can return the data as is */
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if (buffer && buflen > 0) {
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if (buflen > datalen)
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buflen = datalen;
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if (copy_to_user(buffer, rka->callout_info, buflen) != 0)
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ret = -EFAULT;
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}
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return ret;
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}
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/*
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* Handle revocation of an authorisation token key.
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*
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* Called with the key sem write-locked.
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*/
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static void request_key_auth_revoke(struct key *key)
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{
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struct request_key_auth *rka = key->payload.data[0];
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kenter("{%d}", key->serial);
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if (rka->cred) {
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put_cred(rka->cred);
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rka->cred = NULL;
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}
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}
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static void free_request_key_auth(struct request_key_auth *rka)
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{
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if (!rka)
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return;
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key_put(rka->target_key);
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key_put(rka->dest_keyring);
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if (rka->cred)
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put_cred(rka->cred);
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kfree(rka->callout_info);
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kfree(rka);
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}
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/*
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* Destroy an instantiation authorisation token key.
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*/
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static void request_key_auth_destroy(struct key *key)
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{
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struct request_key_auth *rka = key->payload.data[0];
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kenter("{%d}", key->serial);
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free_request_key_auth(rka);
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}
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/*
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* Create an authorisation token for /sbin/request-key or whoever to gain
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* access to the caller's security data.
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*/
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struct key *request_key_auth_new(struct key *target, const void *callout_info,
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size_t callout_len, struct key *dest_keyring)
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{
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struct request_key_auth *rka, *irka;
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const struct cred *cred = current->cred;
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struct key *authkey = NULL;
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char desc[20];
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int ret = -ENOMEM;
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kenter("%d,", target->serial);
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/* allocate a auth record */
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rka = kzalloc(sizeof(*rka), GFP_KERNEL);
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if (!rka)
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goto error;
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rka->callout_info = kmemdup(callout_info, callout_len, GFP_KERNEL);
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if (!rka->callout_info)
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goto error_free_rka;
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rka->callout_len = callout_len;
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/* see if the calling process is already servicing the key request of
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* another process */
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if (cred->request_key_auth) {
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/* it is - use that instantiation context here too */
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down_read(&cred->request_key_auth->sem);
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/* if the auth key has been revoked, then the key we're
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* servicing is already instantiated */
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if (test_bit(KEY_FLAG_REVOKED,
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&cred->request_key_auth->flags)) {
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up_read(&cred->request_key_auth->sem);
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ret = -EKEYREVOKED;
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goto error_free_rka;
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}
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irka = cred->request_key_auth->payload.data[0];
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rka->cred = get_cred(irka->cred);
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rka->pid = irka->pid;
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up_read(&cred->request_key_auth->sem);
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}
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else {
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/* it isn't - use this process as the context */
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rka->cred = get_cred(cred);
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rka->pid = current->pid;
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}
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rka->target_key = key_get(target);
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rka->dest_keyring = key_get(dest_keyring);
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/* allocate the auth key */
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sprintf(desc, "%x", target->serial);
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authkey = key_alloc(&key_type_request_key_auth, desc,
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cred->fsuid, cred->fsgid, cred,
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KEY_POS_VIEW | KEY_POS_READ | KEY_POS_SEARCH |
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KEY_USR_VIEW, KEY_ALLOC_NOT_IN_QUOTA, NULL);
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if (IS_ERR(authkey)) {
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ret = PTR_ERR(authkey);
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goto error_free_rka;
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}
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/* construct the auth key */
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ret = key_instantiate_and_link(authkey, rka, 0, NULL, NULL);
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if (ret < 0)
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goto error_put_authkey;
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kleave(" = {%d,%d}", authkey->serial, refcount_read(&authkey->usage));
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return authkey;
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error_put_authkey:
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key_put(authkey);
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error_free_rka:
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free_request_key_auth(rka);
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error:
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kleave("= %d", ret);
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return ERR_PTR(ret);
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}
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/*
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* Search the current process's keyrings for the authorisation key for
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* instantiation of a key.
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*/
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struct key *key_get_instantiation_authkey(key_serial_t target_id)
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{
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char description[16];
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struct keyring_search_context ctx = {
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.index_key.type = &key_type_request_key_auth,
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.index_key.description = description,
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.cred = current_cred(),
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.match_data.cmp = key_default_cmp,
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.match_data.raw_data = description,
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.match_data.lookup_type = KEYRING_SEARCH_LOOKUP_DIRECT,
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.flags = KEYRING_SEARCH_DO_STATE_CHECK,
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};
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struct key *authkey;
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key_ref_t authkey_ref;
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sprintf(description, "%x", target_id);
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authkey_ref = search_process_keyrings(&ctx);
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if (IS_ERR(authkey_ref)) {
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authkey = ERR_CAST(authkey_ref);
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if (authkey == ERR_PTR(-EAGAIN))
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authkey = ERR_PTR(-ENOKEY);
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goto error;
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}
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authkey = key_ref_to_ptr(authkey_ref);
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if (test_bit(KEY_FLAG_REVOKED, &authkey->flags)) {
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key_put(authkey);
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authkey = ERR_PTR(-EKEYREVOKED);
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}
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error:
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return authkey;
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}
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