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

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Date:   Fri, 17 Jul 2020 14:18:58 -0500
From:   Tyler Hicks <tyhicks@...ux.microsoft.com>
To:     Nayna <nayna@...ux.vnet.ibm.com>,
        Lakshmi Ramasubramanian <nramas@...ux.microsoft.com>
Cc:     Mimi Zohar <zohar@...ux.ibm.com>,
        Dmitry Kasatkin <dmitry.kasatkin@...il.com>,
        James Morris <jmorris@...ei.org>,
        "Serge E . Hallyn" <serge@...lyn.com>,
        Prakhar Srivastava <prsriva02@...il.com>,
        linux-kernel@...r.kernel.org, linux-integrity@...r.kernel.org,
        linux-security-module@...r.kernel.org
Subject: Re: [PATCH v3 06/12] ima: Fail rule parsing when the KEY_CHECK hook
 is combined with an invalid cond

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@...ux.microsoft.com>
> > Reviewed-by: Lakshmi Ramasubramanian <nramas@...ux.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) ||

Tyler

> 
> Thanks & Regards,
> 
>      - Nayna
>