linux/security/keys/persistent.c
David Howells fbf8c53f1a KEYS: Fix UID check in keyctl_get_persistent()
If the UID is specified by userspace when calling the KEYCTL_GET_PERSISTENT
function and the process does not have the CAP_SETUID capability, then the
function will return -EPERM if the current process's uid, suid, euid and fsuid
all match the requested UID.  This is incorrect.

Fix it such that when a non-privileged caller requests a persistent keyring by
a specific UID they can only request their own (ie. the specified UID matches
either then process's UID or the process's EUID).

This can be tested by logging in as the user and doing:

	keyctl get_persistent @p
	keyctl get_persistent @p `id -u`
	keyctl get_persistent @p 0

The first two should successfully print the same key ID.  The third should do
the same if called by UID 0 or indicate Operation Not Permitted otherwise.

Signed-off-by: David Howells <dhowells@redhat.com>
Acked-by: Stephen Gallagher <sgallagh@redhat.com>
2013-11-06 14:01:51 +00:00

168 lines
4.5 KiB
C

/* General persistent per-UID keyrings register
*
* Copyright (C) 2013 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 Licence
* as published by the Free Software Foundation; either version
* 2 of the Licence, or (at your option) any later version.
*/
#include <linux/user_namespace.h>
#include "internal.h"
unsigned persistent_keyring_expiry = 3 * 24 * 3600; /* Expire after 3 days of non-use */
/*
* Create the persistent keyring register for the current user namespace.
*
* Called with the namespace's sem locked for writing.
*/
static int key_create_persistent_register(struct user_namespace *ns)
{
struct key *reg = keyring_alloc(".persistent_register",
KUIDT_INIT(0), KGIDT_INIT(0),
current_cred(),
((KEY_POS_ALL & ~KEY_POS_SETATTR) |
KEY_USR_VIEW | KEY_USR_READ),
KEY_ALLOC_NOT_IN_QUOTA, NULL);
if (IS_ERR(reg))
return PTR_ERR(reg);
ns->persistent_keyring_register = reg;
return 0;
}
/*
* Create the persistent keyring for the specified user.
*
* Called with the namespace's sem locked for writing.
*/
static key_ref_t key_create_persistent(struct user_namespace *ns, kuid_t uid,
struct keyring_index_key *index_key)
{
struct key *persistent;
key_ref_t reg_ref, persistent_ref;
if (!ns->persistent_keyring_register) {
long err = key_create_persistent_register(ns);
if (err < 0)
return ERR_PTR(err);
} else {
reg_ref = make_key_ref(ns->persistent_keyring_register, true);
persistent_ref = find_key_to_update(reg_ref, index_key);
if (persistent_ref)
return persistent_ref;
}
persistent = keyring_alloc(index_key->description,
uid, INVALID_GID, current_cred(),
((KEY_POS_ALL & ~KEY_POS_SETATTR) |
KEY_USR_VIEW | KEY_USR_READ),
KEY_ALLOC_NOT_IN_QUOTA,
ns->persistent_keyring_register);
if (IS_ERR(persistent))
return ERR_CAST(persistent);
return make_key_ref(persistent, true);
}
/*
* Get the persistent keyring for a specific UID and link it to the nominated
* keyring.
*/
static long key_get_persistent(struct user_namespace *ns, kuid_t uid,
key_ref_t dest_ref)
{
struct keyring_index_key index_key;
struct key *persistent;
key_ref_t reg_ref, persistent_ref;
char buf[32];
long ret;
/* Look in the register if it exists */
index_key.type = &key_type_keyring;
index_key.description = buf;
index_key.desc_len = sprintf(buf, "_persistent.%u", from_kuid(ns, uid));
if (ns->persistent_keyring_register) {
reg_ref = make_key_ref(ns->persistent_keyring_register, true);
down_read(&ns->persistent_keyring_register_sem);
persistent_ref = find_key_to_update(reg_ref, &index_key);
up_read(&ns->persistent_keyring_register_sem);
if (persistent_ref)
goto found;
}
/* It wasn't in the register, so we'll need to create it. We might
* also need to create the register.
*/
down_write(&ns->persistent_keyring_register_sem);
persistent_ref = key_create_persistent(ns, uid, &index_key);
up_write(&ns->persistent_keyring_register_sem);
if (!IS_ERR(persistent_ref))
goto found;
return PTR_ERR(persistent_ref);
found:
ret = key_task_permission(persistent_ref, current_cred(), KEY_LINK);
if (ret == 0) {
persistent = key_ref_to_ptr(persistent_ref);
ret = key_link(key_ref_to_ptr(dest_ref), persistent);
if (ret == 0) {
key_set_timeout(persistent, persistent_keyring_expiry);
ret = persistent->serial;
}
}
key_ref_put(persistent_ref);
return ret;
}
/*
* Get the persistent keyring for a specific UID and link it to the nominated
* keyring.
*/
long keyctl_get_persistent(uid_t _uid, key_serial_t destid)
{
struct user_namespace *ns = current_user_ns();
key_ref_t dest_ref;
kuid_t uid;
long ret;
/* -1 indicates the current user */
if (_uid == (uid_t)-1) {
uid = current_uid();
} else {
uid = make_kuid(ns, _uid);
if (!uid_valid(uid))
return -EINVAL;
/* You can only see your own persistent cache if you're not
* sufficiently privileged.
*/
if (!uid_eq(uid, current_uid()) &&
!uid_eq(uid, current_euid()) &&
!ns_capable(ns, CAP_SETUID))
return -EPERM;
}
/* There must be a destination keyring */
dest_ref = lookup_user_key(destid, KEY_LOOKUP_CREATE, KEY_WRITE);
if (IS_ERR(dest_ref))
return PTR_ERR(dest_ref);
if (key_ref_to_ptr(dest_ref)->type != &key_type_keyring) {
ret = -ENOTDIR;
goto out_put_dest;
}
ret = key_get_persistent(ns, uid, dest_ref);
out_put_dest:
key_ref_put(dest_ref);
return ret;
}