Re: [PATCH v8 4/8] IMA: add policy rule to measure critical data

From: Tyler Hicks <tyhicks@linux.microsoft.com>
To: Tushar Sugandhi <tusharsu@linux.microsoft.com>
Cc: zohar@linux.ibm.com, stephen.smalley.work@gmail.com,
	casey@schaufler-ca.com, agk@redhat.com, snitzer@redhat.com,
	gmazyland@gmail.com, paul@paul-moore.com, sashal@kernel.org,
	jmorris@namei.org, nramas@linux.microsoft.com,
	linux-integrity@vger.kernel.org, selinux@vger.kernel.org,
	linux-security-module@vger.kernel.org,
	linux-kernel@vger.kernel.org, dm-devel@redhat.com
Subject: Re: [PATCH v8 4/8] IMA: add policy rule to measure critical data
Date: Fri, 11 Dec 2020 18:25:00 -0600	[thread overview]
Message-ID: <20201212002500.GF4951@sequoia> (raw)
In-Reply-To: <20201211235807.30815-5-tusharsu@linux.microsoft.com>

On 2020-12-11 15:58:03, 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@linux.microsoft.com>
> ---
>  Documentation/ABI/testing/ima_policy |  2 +-
>  security/integrity/ima/ima_policy.c  | 34 ++++++++++++++++++++++++----
>  2 files changed, 31 insertions(+), 5 deletions(-)
> 
> diff --git a/Documentation/ABI/testing/ima_policy b/Documentation/ABI/testing/ima_policy
> index e35263f97fc1..6ec7daa87cba 100644
> --- a/Documentation/ABI/testing/ima_policy
> +++ b/Documentation/ABI/testing/ima_policy
> @@ -32,7 +32,7 @@ Description:
>  			func:= [BPRM_CHECK][MMAP_CHECK][CREDS_CHECK][FILE_CHECK]MODULE_CHECK]
>  			        [FIRMWARE_CHECK]
>  				[KEXEC_KERNEL_CHECK] [KEXEC_INITRAMFS_CHECK]
> -				[KEXEC_CMDLINE] [KEY_CHECK]
> +				[KEXEC_CMDLINE] [KEY_CHECK] [CRITICAL_DATA]
>  			mask:= [[^]MAY_READ] [[^]MAY_WRITE] [[^]MAY_APPEND]
>  			       [[^]MAY_EXEC]
>  			fsmagic:= hex value
> diff --git a/security/integrity/ima/ima_policy.c b/security/integrity/ima/ima_policy.c
> index a09d1a41a290..07116ff35c25 100644
> --- a/security/integrity/ima/ima_policy.c
> +++ b/security/integrity/ima/ima_policy.c
> @@ -85,6 +85,7 @@ 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 */

Argh, there are still some more instances of data_source sneaking into
this patch too early instead of waiting until the next patch.

>  	struct ima_template_desc *template;
>  };
>  
> @@ -479,6 +480,12 @@ static bool ima_match_rule_data(struct ima_rule_entry *rule,
>  
>  		opt_list = rule->keyrings;
>  		break;
> +	case CRITICAL_DATA:
> +		if (!rule->data_source)
> +			return true;
> +
> +		opt_list = rule->data_source;
> +		break;

I guess this case should unconditionally return true in this patch and
then the include this additional logic in the next patch.

Sorry, I missed these on my last review.

Tyler

>  	default:
>  		return false;
>  	}
> @@ -515,13 +522,19 @@ 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;
> @@ -1116,6 +1129,17 @@ 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_FUNC | IMA_UID | IMA_PCR))
> +			return false;
> +
> +		if (ima_rule_contains_lsm_cond(entry))
> +			return false;
> +
>  		break;
>  	default:
>  		return false;
> @@ -1248,6 +1272,8 @@ static int ima_parse_rule(char *rule, struct ima_rule_entry *entry)
>  			else if (IS_ENABLED(CONFIG_IMA_MEASURE_ASYMMETRIC_KEYS) &&
>  				 strcmp(args[0].from, "KEY_CHECK") == 0)
>  				entry->func = KEY_CHECK;
> +			else if (strcmp(args[0].from, "CRITICAL_DATA") == 0)
> +				entry->func = CRITICAL_DATA;
>  			else
>  				result = -EINVAL;
>  			if (!result)
> -- 
> 2.17.1
> 