linux-kernel - Re: [PATCH v1a 1/2] KEYS: validate certificate trust only with selected owner key

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Message-ID: <1402919001.2527.11.camel@dhcp-9-2-203-236.watson.ibm.com>
Date:	Mon, 16 Jun 2014 07:43:21 -0400
From:	Mimi Zohar <zohar@...ux.vnet.ibm.com>
To:	Dmitry Kasatkin <dmitry.kasatkin@...il.com>
Cc:	dhowells@...hat.com, jwboyer@...hat.com, keyrings@...ux-nfs.org,
	linux-security-module@...r.kernel.org,
	linux-kernel@...r.kernel.org,
	Dmitry Kasatkin <d.kasatkin@...sung.com>
Subject: Re: [PATCH v1a 1/2] KEYS: validate certificate trust only with
 selected owner key


On Thu, 2014-06-12 at 23:17 +0300, Dmitry Kasatkin wrote:
> 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.
> 
> This patch defines a new kernel parameter 'keys_ownerid' to specify
> owner's key id which must be used for trust validation of certificates.
> 
> Idea belongs to Mimi Zohar.
> 
> Signed-off-by: Dmitry Kasatkin <d.kasatkin@...sung.com>
> ---
>  Documentation/kernel-parameters.txt      |  5 +++++
>  crypto/asymmetric_keys/x509_public_key.c | 23 +++++++++++++++++++++++
>  2 files changed, 28 insertions(+)
> 
> diff --git a/Documentation/kernel-parameters.txt b/Documentation/kernel-parameters.txt
> index 7116fda..7a810d3 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(s) on
> +			the system trusted keyring to be used for certificate
> +			trust validation.
> +			format: id:<keyid>
> +
>  	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 7a9b386..d46b790 100644
> --- a/crypto/asymmetric_keys/x509_public_key.c
> +++ b/crypto/asymmetric_keys/x509_public_key.c
> @@ -24,6 +24,19 @@
>  #include "public_key.h"
>  #include "x509_parser.h"
> 
> +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);
> +
>  /*
>   * Find a key in the given keyring by issuer and authority.
>   */
> @@ -169,6 +182,16 @@ static int x509_validate_trust(struct x509_certificate *cert,
>  	if (!trust_keyring)
>  		return -EOPNOTSUPP;
> 
> +	if (owner_keyid) {
> +		/* validate trust only with the owner_keyid if specified */
> +		/* partial match of keyid according to the asymmetric_type.c */
> +		int idlen = strlen(owner_keyid) - 3; /* - id: */
> +		int authlen = strlen(cert->authority);
> +		char *auth = cert->authority + authlen - idlen;
> +		if (idlen > authlen || strcasecmp(owner_keyid + 3, auth))
> +			return -EPERM;
> +	}
> +

We shouldn't hard code the test here, but use the key type's match
function.  For example, the "KEYS: define an owner trusted keyring" (v4)
patch defined a key_match() function.  

thanks,

Mimi

>  	key = x509_request_asymmetric_key(trust_keyring,
>  					  cert->issuer, strlen(cert->issuer),
>  					  cert->authority,




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