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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>
212 lines
4.8 KiB
C
212 lines
4.8 KiB
C
/* user_defined.c: user defined key type
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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/init.h>
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#include <linux/slab.h>
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#include <linux/seq_file.h>
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#include <linux/err.h>
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#include <keys/user-type.h>
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#include <linux/uaccess.h>
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#include "internal.h"
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static int logon_vet_description(const char *desc);
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/*
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* user defined keys take an arbitrary string as the description and an
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* arbitrary blob of data as the payload
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*/
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struct key_type key_type_user = {
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.name = "user",
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.preparse = user_preparse,
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.free_preparse = user_free_preparse,
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.instantiate = generic_key_instantiate,
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.update = user_update,
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.revoke = user_revoke,
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.destroy = user_destroy,
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.describe = user_describe,
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.read = user_read,
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};
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EXPORT_SYMBOL_GPL(key_type_user);
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/*
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* This key type is essentially the same as key_type_user, but it does
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* not define a .read op. This is suitable for storing username and
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* password pairs in the keyring that you do not want to be readable
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* from userspace.
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*/
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struct key_type key_type_logon = {
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.name = "logon",
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.preparse = user_preparse,
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.free_preparse = user_free_preparse,
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.instantiate = generic_key_instantiate,
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.update = user_update,
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.revoke = user_revoke,
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.destroy = user_destroy,
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.describe = user_describe,
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.vet_description = logon_vet_description,
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};
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EXPORT_SYMBOL_GPL(key_type_logon);
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/*
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* Preparse a user defined key payload
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*/
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int user_preparse(struct key_preparsed_payload *prep)
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{
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struct user_key_payload *upayload;
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size_t datalen = prep->datalen;
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if (datalen <= 0 || datalen > 32767 || !prep->data)
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return -EINVAL;
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upayload = kmalloc(sizeof(*upayload) + datalen, GFP_KERNEL);
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if (!upayload)
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return -ENOMEM;
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/* attach the data */
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prep->quotalen = datalen;
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prep->payload.data[0] = upayload;
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upayload->datalen = datalen;
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memcpy(upayload->data, prep->data, datalen);
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return 0;
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}
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EXPORT_SYMBOL_GPL(user_preparse);
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/*
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* Free a preparse of a user defined key payload
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*/
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void user_free_preparse(struct key_preparsed_payload *prep)
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{
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kzfree(prep->payload.data[0]);
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}
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EXPORT_SYMBOL_GPL(user_free_preparse);
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static void user_free_payload_rcu(struct rcu_head *head)
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{
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struct user_key_payload *payload;
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payload = container_of(head, struct user_key_payload, rcu);
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kzfree(payload);
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}
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/*
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* update a user defined key
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* - the key's semaphore is write-locked
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*/
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int user_update(struct key *key, struct key_preparsed_payload *prep)
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{
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struct user_key_payload *zap = NULL;
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int ret;
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/* check the quota and attach the new data */
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ret = key_payload_reserve(key, prep->datalen);
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if (ret < 0)
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return ret;
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/* attach the new data, displacing the old */
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key->expiry = prep->expiry;
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if (key_is_positive(key))
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zap = dereference_key_locked(key);
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rcu_assign_keypointer(key, prep->payload.data[0]);
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prep->payload.data[0] = NULL;
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if (zap)
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call_rcu(&zap->rcu, user_free_payload_rcu);
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return ret;
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}
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EXPORT_SYMBOL_GPL(user_update);
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/*
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* dispose of the links from a revoked keyring
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* - called with the key sem write-locked
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*/
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void user_revoke(struct key *key)
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{
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struct user_key_payload *upayload = user_key_payload_locked(key);
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/* clear the quota */
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key_payload_reserve(key, 0);
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if (upayload) {
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rcu_assign_keypointer(key, NULL);
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call_rcu(&upayload->rcu, user_free_payload_rcu);
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}
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}
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EXPORT_SYMBOL(user_revoke);
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/*
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* dispose of the data dangling from the corpse of a user key
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*/
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void user_destroy(struct key *key)
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{
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struct user_key_payload *upayload = key->payload.data[0];
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kzfree(upayload);
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}
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EXPORT_SYMBOL_GPL(user_destroy);
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/*
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* describe the user key
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*/
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void user_describe(const struct key *key, struct seq_file *m)
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{
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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, ": %u", key->datalen);
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}
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EXPORT_SYMBOL_GPL(user_describe);
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/*
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* read the key data
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* - the key's semaphore is read-locked
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*/
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long user_read(const struct key *key, char __user *buffer, size_t buflen)
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{
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const struct user_key_payload *upayload;
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long ret;
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upayload = user_key_payload_locked(key);
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ret = upayload->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 > upayload->datalen)
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buflen = upayload->datalen;
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if (copy_to_user(buffer, upayload->data, 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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EXPORT_SYMBOL_GPL(user_read);
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/* Vet the description for a "logon" key */
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static int logon_vet_description(const char *desc)
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{
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char *p;
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/* require a "qualified" description string */
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p = strchr(desc, ':');
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if (!p)
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return -EINVAL;
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/* also reject description with ':' as first char */
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if (p == desc)
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return -EINVAL;
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return 0;
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}
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