Re: [PATCH 1/4] KEYS: define an owner trusted keyring

[Dmitry Kasatkin]

On 10/06/14 15:24, Josh Boyer wrote:
> On Tue, Jun 10, 2014 at 11:48:15AM +0300, Dmitry Kasatkin wrote:
>> From: Mimi Zohar <zohar@xxxxxxxxxxxxxxxxxx>
>>
>> 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@xxxxxxxxxxxxxxxxxx>
>> ---
>>  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

This patch is original patch and actually I sent it by mistake providing
HEAD~3 instead of HEAD~2 on git-send-email...
But anyway kernel parameter stays...

ok.  case is "unprotected" boot loader.


Thanks.

>>  	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@xxxxxxxxxx>
>> + *
>> + * 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@xxxxxxxxxx>
>> + *
>> + * 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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