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Date: Tue, 10 Jun 2014 08:24:34 -0400
From: Josh Boyer <jwboyer@...hat.com>
To: Dmitry Kasatkin <d.kasatkin@...sung.com>
Cc: zohar@...ux.vnet.ibm.com, dhowells@...hat.com,
keyrings@...ux-nfs.org, linux-security-module@...r.kernel.org,
linux-kernel@...r.kernel.org, dmitry.kasatkin@...il.com,
mjg59@...f.ucam.org
Subject: Re: [PATCH 1/4] KEYS: define an owner trusted keyring
On Tue, Jun 10, 2014 at 11:48:15AM +0300, Dmitry Kasatkin wrote:
> From: Mimi Zohar <zohar@...ux.vnet.ibm.com>
>
> Instead of allowing public keys, with certificates signed by any
> key on the system trusted keyring, to be added to a trusted
> keyring, this patch further restricts the certificates to those
> signed by a particular key on the system keyring.
>
> When the UEFI secure boot keys are added to the system keyring, the
> platform owner will be able to load their key in one of the UEFI DBs
> (eg. Machine Owner Key(MOK) list) and select their key, without
> having to rebuild the kernel.
>
> This patch defines an owner trusted keyring, a new boot command
> line option 'keys_ownerid=', and defines a new function
> get_system_or_owner_trusted_keyring().
>
> Signed-off-by: Mimi Zohar<zohar@...ux.vnet.ibm.com>
> ---
> Documentation/kernel-parameters.txt | 5 ++
> crypto/asymmetric_keys/x509_public_key.c | 4 +-
> include/keys/owner_keyring.h | 27 ++++++++++
> init/Kconfig | 10 ++++
> kernel/Makefile | 1 +
> kernel/owner_keyring.c | 85 ++++++++++++++++++++++++++++++++
> 6 files changed, 131 insertions(+), 1 deletion(-)
> create mode 100644 include/keys/owner_keyring.h
> create mode 100644 kernel/owner_keyring.c
>
> diff --git a/Documentation/kernel-parameters.txt b/Documentation/kernel-parameters.txt
> index 7116fda..f90d31d 100644
> --- a/Documentation/kernel-parameters.txt
> +++ b/Documentation/kernel-parameters.txt
> @@ -1434,6 +1434,11 @@ bytes respectively. Such letter suffixes can also be entirely omitted.
> use the HighMem zone if it exists, and the Normal
> zone if it does not.
>
> + keys_ownerid=[KEYS] This parameter identifies a specific key on
> + the system trusted keyring to be added to the
> + owner trusted keyring.
> + format: id:<keyid>
> +
I'm fairly sure this runs into the same problems I mentioned previously
in the secure boot context. Namely that a remote attacker could modify
keys_ownerid in the bootloader config file if they gained root access.
josh
> kgdbdbgp= [KGDB,HW] kgdb over EHCI usb debug port.
> Format: <Controller#>[,poll interval]
> The controller # is the number of the ehci usb debug
> diff --git a/crypto/asymmetric_keys/x509_public_key.c b/crypto/asymmetric_keys/x509_public_key.c
> index 1af8a30..6af338f 100644
> --- a/crypto/asymmetric_keys/x509_public_key.c
> +++ b/crypto/asymmetric_keys/x509_public_key.c
> @@ -19,6 +19,7 @@
> #include <keys/asymmetric-subtype.h>
> #include <keys/asymmetric-parser.h>
> #include <keys/system_keyring.h>
> +#include <keys/owner_keyring.h>
> #include <crypto/hash.h>
> #include "asymmetric_keys.h"
> #include "public_key.h"
> @@ -237,7 +238,8 @@ static int x509_key_preparse(struct key_preparsed_payload *prep)
> if (ret < 0)
> goto error_free_cert;
> } else {
> - ret = x509_validate_trust(cert, get_system_trusted_keyring());
> + ret = x509_validate_trust(cert,
> + get_system_or_owner_trusted_keyring());
> if (!ret)
> prep->trusted = 1;
> }
> diff --git a/include/keys/owner_keyring.h b/include/keys/owner_keyring.h
> new file mode 100644
> index 0000000..78dd09d
> --- /dev/null
> +++ b/include/keys/owner_keyring.h
> @@ -0,0 +1,27 @@
> +/*
> + * Copyright (C) 2014 IBM Corporation
> + * Author: Mimi Zohar <zohar@...ibm.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, version 2 of the License.
> + */
> +
> +#ifndef _KEYS_OWNER_KEYRING_H
> +#define _KEYS_OWNER_KEYRING_H
> +
> +#ifdef CONFIG_OWNER_TRUSTED_KEYRING
> +
> +#include <linux/key.h>
> +
> +extern struct key *owner_trusted_keyring;
> +extern struct key *get_system_or_owner_trusted_keyring(void);
> +
> +#else
> +static inline struct key *get_system_or_owner_trusted_keyring(void)
> +{
> + return get_system_trusted_keyring();
> +}
> +
> +#endif
> +#endif /* _KEYS_OWNER_KEYRING_H */
> diff --git a/init/Kconfig b/init/Kconfig
> index 009a797..7876787 100644
> --- a/init/Kconfig
> +++ b/init/Kconfig
> @@ -1661,6 +1661,16 @@ config SYSTEM_TRUSTED_KEYRING
>
> Keys in this keyring are used by module signature checking.
>
> +config OWNER_TRUSTED_KEYRING
> + bool "Verify certificate signatures using a specific system key"
> + depends on SYSTEM_TRUSTED_KEYRING
> + help
> + Verify a certificate's signature, before adding the key to
> + a trusted keyring, using a specific key on the system trusted
> + keyring. The specific key on the system trusted keyring is
> + identified using the kernel boot command line option
> + "keys_ownerid" and is added to the owner_trusted_keyring.
> +
> menuconfig MODULES
> bool "Enable loadable module support"
> option modules
> diff --git a/kernel/Makefile b/kernel/Makefile
> index bc010ee..7b44efd 100644
> --- a/kernel/Makefile
> +++ b/kernel/Makefile
> @@ -44,6 +44,7 @@ obj-$(CONFIG_UID16) += uid16.o
> obj-$(CONFIG_SYSTEM_TRUSTED_KEYRING) += system_keyring.o system_certificates.o
> obj-$(CONFIG_MODULES) += module.o
> obj-$(CONFIG_MODULE_SIG) += module_signing.o
> +obj-$(CONFIG_OWNER_TRUSTED_KEYRING) += owner_keyring.o
> obj-$(CONFIG_KALLSYMS) += kallsyms.o
> obj-$(CONFIG_BSD_PROCESS_ACCT) += acct.o
> obj-$(CONFIG_KEXEC) += kexec.o
> diff --git a/kernel/owner_keyring.c b/kernel/owner_keyring.c
> new file mode 100644
> index 0000000..a31b865
> --- /dev/null
> +++ b/kernel/owner_keyring.c
> @@ -0,0 +1,85 @@
> +/*
> + * Copyright (C) 2014 IBM Corporation
> + * Author: Mimi Zohar <zohar@...ibm.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, version 2 of the License.
> + */
> +
> +#include <linux/export.h>
> +#include <linux/kernel.h>
> +#include <linux/sched.h>
> +#include <linux/cred.h>
> +#include <linux/err.h>
> +#include <keys/asymmetric-type.h>
> +#include <keys/system_keyring.h>
> +#include "module-internal.h"
> +
> +struct key *owner_trusted_keyring;
> +static int use_owner_trusted_keyring;
> +
> +static char *owner_keyid;
> +static int __init default_owner_keyid_set(char *str)
> +{
> + if (!str) /* default system keyring */
> + return 1;
> +
> + if (strncmp(str, "id:", 3) == 0)
> + owner_keyid = str; /* owner local key 'id:xxxxxx' */
> +
> + return 1;
> +}
> +
> +__setup("keys_ownerid=", default_owner_keyid_set);
> +
> +struct key *get_system_or_owner_trusted_keyring(void)
> +{
> + return use_owner_trusted_keyring ? owner_trusted_keyring :
> + get_system_trusted_keyring();
> +}
> +
> +static __init int owner_trusted_keyring_init(void)
> +{
> + pr_notice("Initialize the owner trusted keyring\n");
> +
> + owner_trusted_keyring =
> + keyring_alloc(".owner_keyring",
> + KUIDT_INIT(0), KGIDT_INIT(0), current_cred(),
> + ((KEY_POS_ALL & ~KEY_POS_SETATTR) |
> + KEY_USR_VIEW | KEY_USR_READ | KEY_USR_SEARCH),
> + KEY_ALLOC_NOT_IN_QUOTA, NULL);
> + if (IS_ERR(owner_trusted_keyring))
> + panic("Can't allocate owner trusted keyring\n");
> +
> + set_bit(KEY_FLAG_TRUSTED_ONLY, &owner_trusted_keyring->flags);
> + return 0;
> +}
> +
> +device_initcall(owner_trusted_keyring_init);
> +
> +void load_owner_identified_key(void)
> +{
> + key_ref_t key_ref;
> + int ret;
> +
> + if (!owner_keyid)
> + return;
> +
> + key_ref = keyring_search(make_key_ref(system_trusted_keyring, 1),
> + &key_type_asymmetric, owner_keyid);
> + if (IS_ERR(key_ref)) {
> + pr_warn("Request for unknown %s key\n", owner_keyid);
> + goto out;
> + }
> + ret = key_link(owner_trusted_keyring, key_ref_to_ptr(key_ref));
> + pr_info("Loaded owner key %s %s\n", owner_keyid,
> + ret < 0 ? "failed" : "succeeded");
> + key_ref_put(key_ref);
> + if (!ret)
> + use_owner_trusted_keyring = 1;
> +out:
> + return;
> +}
> +
> +late_initcall(load_owner_identified_key);
> --
> 1.9.1
>
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