[PATCH v9 5/8] IMA: limit critical data measurement based on a label

[Tyler Hicks]

On 2020-12-12 10:02:48, Tushar Sugandhi wrote:
> System administrators should be able to limit which kernel subsystems
> they want to measure the critical data for. To enable that, an IMA policy
> condition to choose specific kernel subsystems is needed. This policy
> condition would constrain the measurement of the critical data based on
> a label for the given subsystems.
> 
> Add a new IMA policy condition - "data_source:=" to the IMA func
> CRITICAL_DATA to allow measurement of various kernel subsystems. This
> policy condition would enable the system administrators to restrict the
> measurement to the labels listed in "data_source:=".
> 
> Limit the measurement to the labels that are specified in the IMA
> policy - CRITICAL_DATA+"data_source:=". If "data_sources:=" is not
> provided with the func CRITICAL_DATA, the data from all the
> supported kernel subsystems is measured.
> 
> Signed-off-by: Tushar Sugandhi <tusharsu at linux.microsoft.com>

Reviewed-by: Tyler Hicks <tyhicks at linux.microsoft.com>

Tyler

> ---
>  Documentation/ABI/testing/ima_policy |  2 ++
>  security/integrity/ima/ima_policy.c  | 37 +++++++++++++++++++++++++---
>  2 files changed, 36 insertions(+), 3 deletions(-)
> 
> diff --git a/Documentation/ABI/testing/ima_policy b/Documentation/ABI/testing/ima_policy
> index 6ec7daa87cba..0f4ee9e0a455 100644
> --- a/Documentation/ABI/testing/ima_policy
> +++ b/Documentation/ABI/testing/ima_policy
> @@ -52,6 +52,8 @@ Description:
>  			template:= name of a defined IMA template type
>  			(eg, ima-ng). Only valid when action is "measure".
>  			pcr:= decimal value
> +			data_source:= [label]
> +			label:= a unique string used for grouping and limiting critical data.
>  
>  		  default policy:
>  			# PROC_SUPER_MAGIC
> diff --git a/security/integrity/ima/ima_policy.c b/security/integrity/ima/ima_policy.c
> index d45c2dbb6d45..fea996a9e26c 100644
> --- a/security/integrity/ima/ima_policy.c
> +++ b/security/integrity/ima/ima_policy.c
> @@ -34,6 +34,7 @@
>  #define IMA_PCR		0x0100
>  #define IMA_FSNAME	0x0200
>  #define IMA_KEYRINGS	0x0400
> +#define IMA_DATA_SOURCE	0x0800
>  
>  #define UNKNOWN		0
>  #define MEASURE		0x0001	/* same as IMA_MEASURE */
> @@ -85,6 +86,7 @@ struct ima_rule_entry {
>  	} lsm[MAX_LSM_RULES];
>  	char *fsname;
>  	struct ima_rule_opt_list *keyrings; /* Measure keys added to these keyrings */
> +	struct ima_rule_opt_list *data_source; /* Measure data from this source */
>  	struct ima_template_desc *template;
>  };
>  
> @@ -480,7 +482,11 @@ static bool ima_match_rule_data(struct ima_rule_entry *rule,
>  		opt_list = rule->keyrings;
>  		break;
>  	case CRITICAL_DATA:
> -		return true;
> +		if (!rule->data_source)
> +			return true;
> +
> +		opt_list = rule->data_source;
> +		break;
>  	default:
>  		return false;
>  	}
> @@ -925,7 +931,7 @@ enum {
>  	Opt_uid_lt, Opt_euid_lt, Opt_fowner_lt,
>  	Opt_appraise_type, Opt_appraise_flag,
>  	Opt_permit_directio, Opt_pcr, Opt_template, Opt_keyrings,
> -	Opt_err
> +	Opt_data_source, Opt_err
>  };
>  
>  static const match_table_t policy_tokens = {
> @@ -962,6 +968,7 @@ static const match_table_t policy_tokens = {
>  	{Opt_pcr, "pcr=%s"},
>  	{Opt_template, "template=%s"},
>  	{Opt_keyrings, "keyrings=%s"},
> +	{Opt_data_source, "data_source=%s"},
>  	{Opt_err, NULL}
>  };
>  
> @@ -1129,7 +1136,8 @@ static bool ima_validate_rule(struct ima_rule_entry *entry)
>  		if (entry->action & ~(MEASURE | DONT_MEASURE))
>  			return false;
>  
> -		if (entry->flags & ~(IMA_FUNC | IMA_UID | IMA_PCR))
> +		if (entry->flags & ~(IMA_FUNC | IMA_UID | IMA_PCR |
> +				     IMA_DATA_SOURCE))
>  			return false;
>  
>  		if (ima_rule_contains_lsm_cond(entry))
> @@ -1339,6 +1347,23 @@ static int ima_parse_rule(char *rule, struct ima_rule_entry *entry)
>  
>  			entry->flags |= IMA_KEYRINGS;
>  			break;
> +		case Opt_data_source:
> +			ima_log_string(ab, "data_source", args[0].from);
> +
> +			if (entry->data_source) {
> +				result = -EINVAL;
> +				break;
> +			}
> +
> +			entry->data_source = ima_alloc_rule_opt_list(args);
> +			if (IS_ERR(entry->data_source)) {
> +				result = PTR_ERR(entry->data_source);
> +				entry->data_source = NULL;
> +				break;
> +			}
> +
> +			entry->flags |= IMA_DATA_SOURCE;
> +			break;
>  		case Opt_fsuuid:
>  			ima_log_string(ab, "fsuuid", args[0].from);
>  
> @@ -1719,6 +1744,12 @@ int ima_policy_show(struct seq_file *m, void *v)
>  		seq_puts(m, " ");
>  	}
>  
> +	if (entry->flags & IMA_DATA_SOURCE) {
> +		seq_puts(m, "data_source=");
> +		ima_show_rule_opt_list(m, entry->data_source);
> +		seq_puts(m, " ");
> +	}
> +
>  	if (entry->flags & IMA_PCR) {
>  		snprintf(tbuf, sizeof(tbuf), "%d", entry->pcr);
>  		seq_printf(m, pt(Opt_pcr), tbuf);
> -- 
> 2.17.1
>