linux-kernel - Re: [PATCH v10 5/6] IMA: Add support to limit measuring keys

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Date:   Tue, 10 Dec 2019 17:43:25 -0500
From:   Mimi Zohar <zohar@...ux.ibm.com>
To:     Lakshmi Ramasubramanian <nramas@...ux.microsoft.com>,
        linux-integrity@...r.kernel.org
Cc:     eric.snowberg@...cle.com, dhowells@...hat.com,
        mathew.j.martineau@...ux.intel.com, matthewgarrett@...gle.com,
        sashal@...nel.org, jamorris@...ux.microsoft.com,
        linux-kernel@...r.kernel.org, keyrings@...r.kernel.org
Subject: Re: [PATCH v10 5/6] IMA: Add support to limit measuring keys

On Wed, 2019-12-04 at 14:41 -0800, Lakshmi Ramasubramanian wrote:
> diff --git a/security/integrity/ima/ima_policy.c b/security/integrity/ima/ima_policy.c
> index 1525a28fd705..5db990c8b02d 100644
> --- a/security/integrity/ima/ima_policy.c
> +++ b/security/integrity/ima/ima_policy.c
> @@ -356,6 +357,51 @@ int ima_lsm_policy_change(struct notifier_block *nb, unsigned long event,
>  	return NOTIFY_OK;
>  }
>  
> +/**
> + * ima_match_keyring - determine whether the keyring matches the measure rule
> + * @rule: a pointer to a rule
> + * @keyring: name of the keyring to match against the measure rule
> + * @cred: a pointer to a credentials structure for user validation
> + *
> + * Returns true if keyring matches one in the rule, false otherwise.
> + */
> +static bool ima_match_keyring(struct ima_rule_entry *rule,
> +			      const char *keyring, const struct cred *cred)
> +{
> +	char *keyrings, *next_keyring, *keyrings_ptr;
> +	bool matched = false;
> +
> +	/* If "keyrings=" is not specified all keys are measured. */

With the addiitonal "uid" support this isn't necessarily true any
more.

Mimi

> +	if (!rule->keyrings)
> +		return true;
> +
> +	if (!keyring)
> +		return false;
> +
> +	if ((rule->flags & IMA_UID) && !rule->uid_op(cred->uid, rule->uid))
> +		return false;
> +
> +	keyrings = kstrdup(rule->keyrings, GFP_KERNEL);
> +	if (!keyrings)
> +		return false;
> +
> +	/*
> +	 * "keyrings=" is specified in the policy in the format below:
> +	 * keyrings=.builtin_trusted_keys|.ima|.evm
> +	 */
> +	keyrings_ptr = keyrings;
> +	while ((next_keyring = strsep(&keyrings_ptr, "|")) != NULL) {
> +		if (!strcmp(next_keyring, keyring)) {
> +			matched = true;
> +			break;
> +		}
> +	}
> +
> +	kfree(keyrings);
> +
> +	return matched;
> +}
> +