linux-kernel - Re: [PATCH v7 4/8] IMA: add policy rule to measure critical data

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Message-ID: <20201210231045.GI489768@sequoia>
Date:   Thu, 10 Dec 2020 17:10:45 -0600
From:   Tyler Hicks <tyhicks@...ux.microsoft.com>
To:     Tushar Sugandhi <tusharsu@...ux.microsoft.com>
Cc:     zohar@...ux.ibm.com, stephen.smalley.work@...il.com,
        casey@...aufler-ca.com, agk@...hat.com, snitzer@...hat.com,
        gmazyland@...il.com, paul@...l-moore.com, sashal@...nel.org,
        jmorris@...ei.org, nramas@...ux.microsoft.com,
        linux-integrity@...r.kernel.org, selinux@...r.kernel.org,
        linux-security-module@...r.kernel.org,
        linux-kernel@...r.kernel.org, dm-devel@...hat.com
Subject: Re: [PATCH v7 4/8] IMA: add policy rule to measure critical data

On 2020-12-09 11:42:08, Tushar Sugandhi wrote:
> A new IMA policy rule is needed for the IMA hook
> ima_measure_critical_data() and the corresponding func CRITICAL_DATA for
> measuring the input buffer. The policy rule should ensure the buffer
> would get measured only when the policy rule allows the action. The
> policy rule should also support the necessary constraints (flags etc.)
> for integrity critical buffer data measurements.
> 
> Add a policy rule to define the constraints for restricting integrity
> critical data measurements.
> 
> Signed-off-by: Tushar Sugandhi <tusharsu@...ux.microsoft.com>
> ---
>  security/integrity/ima/ima_policy.c | 35 +++++++++++++++++++++++++----
>  1 file changed, 31 insertions(+), 4 deletions(-)
> 
> diff --git a/security/integrity/ima/ima_policy.c b/security/integrity/ima/ima_policy.c
> index 2a0c0603626e..9a8ee80a3128 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

You introduce data_source= in the next patch. This macro shouldn't be
added until the next patch.

>  
>  #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;
>  };
>  
> @@ -479,6 +481,12 @@ static bool ima_match_rule_data(struct ima_rule_entry *rule,
>  		else
>  			opt_list = rule->keyrings;
>  		break;
> +	case CRITICAL_DATA:
> +		if (!rule->data_source)
> +			return true;
> +		else
> +			opt_list = rule->data_source;

If you take my suggestions on patch #1, remove the else and simply
assign opt_list here, too.

> +		break;
>  	default:
>  		break;
>  	}
> @@ -518,13 +526,19 @@ static bool ima_match_rules(struct ima_rule_entry *rule, struct inode *inode,
>  {
>  	int i;
>  
> -	if (func == KEY_CHECK) {
> -		return (rule->flags & IMA_FUNC) && (rule->func == func) &&
> -			ima_match_rule_data(rule, func_data, cred);
> -	}
>  	if ((rule->flags & IMA_FUNC) &&
>  	    (rule->func != func && func != POST_SETATTR))
>  		return false;
> +
> +	switch (func) {
> +	case KEY_CHECK:
> +	case CRITICAL_DATA:
> +		return ((rule->func == func) &&
> +			ima_match_rule_data(rule, func_data, cred));
> +	default:
> +		break;
> +	}
> +
>  	if ((rule->flags & IMA_MASK) &&
>  	    (rule->mask != mask && func != POST_SETATTR))
>  		return false;
> @@ -1119,6 +1133,19 @@ static bool ima_validate_rule(struct ima_rule_entry *entry)
>  		if (ima_rule_contains_lsm_cond(entry))
>  			return false;
>  
> +		break;
> +	case CRITICAL_DATA:
> +		if (entry->action & ~(MEASURE | DONT_MEASURE))
> +			return false;
> +
> +		if (!(entry->flags & IMA_DATA_SOURCE) ||
> +		    (entry->flags & ~(IMA_FUNC | IMA_UID | IMA_PCR |
> +		    IMA_DATA_SOURCE)))

IMA_DATA_SOURCE shouldn't exist in this patch. This isn't the right
indentation, either. See how IMA_KEYRINGS is indented in the KEY_CHECK
case above.

Tyler

> +			return false;
> +
> +		if (ima_rule_contains_lsm_cond(entry))
> +			return false;
> +
>  		break;
>  	default:
>  		return false;
> -- 
> 2.17.1
>