Re: [PATCH v3 06/12] ima: Fail rule parsing when the KEY_CHECK hook is combined with an invalid cond

From: Tyler Hicks <tyhicks@linux.microsoft.com>
To: Nayna <nayna@linux.vnet.ibm.com>,
	Lakshmi Ramasubramanian <nramas@linux.microsoft.com>,
	Mimi Zohar <zohar@linux.ibm.com>
Cc: Dmitry Kasatkin <dmitry.kasatkin@gmail.com>,
	James Morris <jmorris@namei.org>,
	"Serge E . Hallyn" <serge@hallyn.com>,
	Prakhar Srivastava <prsriva02@gmail.com>,
	linux-kernel@vger.kernel.org, linux-integrity@vger.kernel.org,
	linux-security-module@vger.kernel.org
Subject: Re: [PATCH v3 06/12] ima: Fail rule parsing when the KEY_CHECK hook is combined with an invalid cond
Date: Fri, 17 Jul 2020 18:39:59 -0500	[thread overview]
Message-ID: <20200717233959.GP3673@sequoia> (raw)
In-Reply-To: <20200717191858.GN3673@sequoia>

On 2020-07-17 14:19:03, Tyler Hicks wrote:
> On 2020-07-17 14:56:46, Nayna wrote:
> > 
> > On 7/9/20 2:19 AM, Tyler Hicks wrote:
> > > The KEY_CHECK function only supports the uid, pcr, and keyrings
> > > conditionals. Make this clear at policy load so that IMA policy authors
> > > don't assume that other conditionals are supported.
> > > 
> > > Fixes: 5808611cccb2 ("IMA: Add KEY_CHECK func to measure keys")
> > > Signed-off-by: Tyler Hicks <tyhicks@linux.microsoft.com>
> > > Reviewed-by: Lakshmi Ramasubramanian <nramas@linux.microsoft.com>
> > > ---
> > > 
> > > * v3
> > >    - Added Lakshmi's Reviewed-by
> > >    - Adjust for the indentation change introduced in patch #4
> > > * v2
> > >    - No change
> > > 
> > >   security/integrity/ima/ima_policy.c | 7 +++++++
> > >   1 file changed, 7 insertions(+)
> > > 
> > > diff --git a/security/integrity/ima/ima_policy.c b/security/integrity/ima/ima_policy.c
> > > index 1c64bd6f1728..81da02071d41 100644
> > > --- a/security/integrity/ima/ima_policy.c
> > > +++ b/security/integrity/ima/ima_policy.c
> > > @@ -1023,6 +1023,13 @@ static bool ima_validate_rule(struct ima_rule_entry *entry)
> > >   		if (entry->action & ~(MEASURE | DONT_MEASURE))
> > >   			return false;
> > > 
> > > +		if (entry->flags & ~(IMA_FUNC | IMA_UID | IMA_PCR |
> > > +				     IMA_KEYRINGS))
> > > +			return false;
> > > +
> > > +		if (ima_rule_contains_lsm_cond(entry))
> > > +			return false;
> > > +
> > >   		break;
> > >   	default:
> > >   		return false;
> > 
> > Should there be a check for IMA_MEASURE_ASYMMETRIC_KEYS in Opt_keyrings in
> > ima_parse_rule() to return immediately if not enabled ?
> 
> I didn't notice that "keyrings=" could be disabled at build time. I
> think you're right that something like what I have below would be a good idea.
> 
> @Lakshmi, do you agree?
> 
> diff --git a/security/integrity/ima/ima_policy.c b/security/integrity/ima/ima_policy.c
> index 81da02071d41..bd687560f88e 100644
> --- a/security/integrity/ima/ima_policy.c
> +++ b/security/integrity/ima/ima_policy.c
> @@ -1212,6 +1212,11 @@ static int ima_parse_rule(char *rule, struct ima_rule_entry *entry)
>  		case Opt_keyrings:
>  			ima_log_string(ab, "keyrings", args[0].from);
>  
> +			if (!IS_ENABLED(CONFIG_IMA_MEASURE_ASYMMETRIC_KEYS)) {
> +				result = -EINVAL;
> +				break;
> +			}
> +
>  			keyrings_len = strlen(args[0].from) + 1;
>  
>  			if ((entry->keyrings) ||
> 

Actually, this change introduces a new compiler warning in another part
of the code that I need to think some more about. I'd like to leave this
patch as-is for now and work on the !CONFIG_IMA_MEASURE_ASYMMETRIC_KEYS
case in a separate, later patch when I have some more time to think
about it and test properly.

Tyler

> Tyler
> 
> > 
> > Thanks & Regards,
> > 
> >      - Nayna
> > 