linux-kernel - Re: [PATCH 3/3] IMA: add support to measure duplicate buffer for critical data hook

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Message-ID: <8af5bf67-54d3-f358-6cb6-34733fc72df2@linux.microsoft.com>
Date:   Tue, 9 Feb 2021 10:31:43 -0800
From:   Tushar Sugandhi <tusharsu@...ux.microsoft.com>
To:     Mimi Zohar <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
Cc:     tyhicks@...ux.microsoft.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 3/3] IMA: add support to measure duplicate buffer for
 critical data hook



On 2021-02-08 12:24 p.m., Mimi Zohar wrote:
> Hi Tushar,
> 
> On Fri, 2021-01-29 at 16:45 -0800, Tushar Sugandhi wrote:
> 
>> diff --git a/security/integrity/ima/ima_queue.c b/security/integrity/ima/ima_queue.c
>>
>> index c096ef8945c7..fbf359495fa8 100644
>> --- a/security/integrity/ima/ima_queue.c
>> +++ b/security/integrity/ima/ima_queue.c
>> @@ -158,7 +158,7 @@ static int ima_pcr_extend(struct tpm_digest *digests_arg, int pcr)
>>    */
>>   int ima_add_template_entry(struct ima_template_entry *entry, int violation,
>>   			   const char *op, struct inode *inode,
>> -			   const unsigned char *filename)
>> +			   const unsigned char *filename, bool allow_dup)
>>   {
>>   	u8 *digest = entry->digests[ima_hash_algo_idx].digest;
>>
>   	struct tpm_digestate_entry(struct ima_template_entry *entry, int violation,
Not sure I understand this.  Maybe a typo?  Could you please explain?

>>   
>>   	mutex_lock(&ima_extend_list_mutex);
>>   	if (!violation) {
>> -		if (ima_lookup_digest_entry(digest, entry->pcr)) {
>> +		if (!allow_dup &&
>> +		    ima_lookup_digest_entry(digest, entry->pcr)) {
> 
> Can't this change be simplified to "if (!violation && !allow_dup)"?
> 
Sure.  Will do.

Earlier I wasn't sure if 'violation' would touch any other use-cases 
inadvertently.  That's why I localized the change as above.

But now since we are supporting other scenarios as well,
I believe "if (!violation && !allow_dup)" would be cleaner.

> Also perhaps instead of passing another variable "allow_dup" to each of
> these functions, pass a mask containing violation and allow_dup.
> 
There were examples of both approaches in ima_match_policy().
  - int *pcr/ima_template_desc **template_desc as an out-param;
  - and various actions as flags in return int.

Earlier I couldn't decide one way or the other, so I picked the 
out-param approach.

But since allow_dup is just a single bit info, returning it as a bit in 
the action flag is a cleaner solution.
Will implement it with flag in the next iteration.

Thanks again for reviewing the series.  Really appreciate it.

Thanks,
Tushar

>>   			audit_cause = "hash_exists";
>>   			result = -EEXIST;
>>   			goto out;
> 
> thanks,
> 
> Mimi
>