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

[Tushar Sugandhi]

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