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SubjectRe: [PATCH v5 1/4] IMA: Add func to measure LSM state and policy
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On 7/30/20 8:02 AM, Tyler Hicks wrote:

>> diff --git a/security/integrity/ima/ima_policy.c b/security/integrity/ima/ima_policy.c
>> index 07f033634b27..a0f5c39d9084 100644
>> --- a/security/integrity/ima/ima_policy.c
>> +++ b/security/integrity/ima/ima_policy.c
>> @@ -442,13 +442,20 @@ 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_keyring(rule, keyring, cred);
>> - }
>> if ((rule->flags & IMA_FUNC) &&
>> (rule->func != func && func != POST_SETATTR))
>> return false;
>> +
>> + switch (func) {
>> + case KEY_CHECK:
>> + return ima_match_keyring(rule, keyring, cred);
>> + case LSM_STATE:
>> + case LSM_POLICY:
>> + return true;
>> + default:
>> + break;
>> + }
>> +
>> if ((rule->flags & IMA_MASK) &&
>> (rule->mask != mask && func != POST_SETATTR))
>> return false;
>> @@ -1044,6 +1051,18 @@ static bool ima_validate_rule(struct ima_rule_entry *entry)
>> if (ima_rule_contains_lsm_cond(entry))
>> return false;
>>
>> + break;
>> + case LSM_STATE:
>> + case LSM_POLICY:
>> + if (entry->action & ~(MEASURE | DONT_MEASURE))
>> + return false;
>> +
>> + if (entry->flags & ~(IMA_FUNC | IMA_PCR))
>> + return false;
>> +
>> + if (ima_rule_contains_lsm_cond(entry))
>> + return false;
>> +
>> break;
>> default:
>> return false;
>> @@ -1176,6 +1195,10 @@ static int ima_parse_rule(char *rule, struct ima_rule_entry *entry)
>> entry->func = KEXEC_CMDLINE;
>> else if (strcmp(args[0].from, "KEY_CHECK") == 0)
>> entry->func = KEY_CHECK;
>> + else if (strcmp(args[0].from, "LSM_STATE") == 0)
>> + entry->func = LSM_STATE;
>> + else if (strcmp(args[0].from, "LSM_POLICY") == 0)
>> + entry->func = LSM_POLICY;
>
> This patch generally looks really good to me with the exception of one
> thing...
>
> We should only accept rules with these specified hook functions when an
> LSM that has measurement support is enabled. This messes up the ordering
> of your patch series but it could be as simple as doing this:
>
> else if (IS_ENABLED(CONFIG_SECURITY_SELINUX) &&
> strcmp(args[0].from, "LSM_STATE") == 0)
> entry->func = LSM_STATE;
>
> Or you could do something a little more complex, like what's done with
> CONFIG_IMA_LSM_RULES. You could create a CONFIG_IMA_MEASURE_LSM option
> that's default enabled but depends on CONFIG_SECURITY_SELINUX and then
> check for IS_ENABLED(CONFIG_IMA_MEASURE_LSM) in ima_parse_rule().
>
> I'd personally opt for just placing the
> IS_ENABLED(CONFIG_SECURITY_SELINUX) check directly into
> ima_parse_rule().
>

The LSM hook can be used by any security module (not just SELinux) to
measure their data.

I have implemented measurement in SELinux to illustrate the usage.
Maybe, I can add the check you have suggested for now and when more
security modules start using this IMA policy additional checks can be
added as appropriate.

thanks,
-lakshmi

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