linux-kernel - Re: [PATCH v2 09/11] ima: Move validation of the keyrings conditional into ima_validate

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Message-ID: <20200629141614.GD4694@sequoia>
Date:   Mon, 29 Jun 2020 09:16:14 -0500
From:   Tyler Hicks <tyhicks@...ux.microsoft.com>
To:     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 v2 09/11] ima: Move validation of the keyrings
 conditional into ima_validate_rule()

On 2020-06-27 16:49:46, Lakshmi Ramasubramanian wrote:
> On 6/26/20 3:38 PM, Tyler Hicks wrote:
> 
> > Use ima_validate_rule() to ensure that the combination of a hook
> > function and the keyrings conditional is valid and that the keyrings
> > conditional is not specified without an explicit KEY_CHECK func
> > conditional. This is a code cleanup and has no user-facing change.
> 
> In addition to checking for func=KEY_CHECK and the keyrings conditional, the
> patch also validates the flags for other IMA hooks (such as
> KEXEC_KERNEL_CHECK, POLICY_CHECK, etc.) Would be good to mention that in the
> patch description.

It actually doesn't do any additional validation of other IMA hooks at
this time. That check on entry->flags is an allowlist of every possible
conditional flag except IMA_KEYRINGS. The ima_parse_rule() function is
already validating all of these conditional flags.

Tyler

> 
>  -lakshmi
> 
> > 
> > Signed-off-by: Tyler Hicks <tyhicks@...ux.microsoft.com>
> > ---
> > 
> > * v2
> >    - Allowed IMA_DIGSIG_REQUIRED, IMA_PERMIT_DIRECTIO,
> >      IMA_MODSIG_ALLOWED, and IMA_CHECK_BLACKLIST conditionals to be
> >      present in the rule entry flags for non-buffer hook functions.
> > 
> >   security/integrity/ima/ima_policy.c | 13 +++++++++++--
> >   1 file changed, 11 insertions(+), 2 deletions(-)
> > 
> > diff --git a/security/integrity/ima/ima_policy.c b/security/integrity/ima/ima_policy.c
> > index 8cdca2399d59..43d49ad958fb 100644
> > --- a/security/integrity/ima/ima_policy.c
> > +++ b/security/integrity/ima/ima_policy.c
> > @@ -1000,6 +1000,15 @@ static bool ima_validate_rule(struct ima_rule_entry *entry)
> >   		case KEXEC_KERNEL_CHECK:
> >   		case KEXEC_INITRAMFS_CHECK:
> >   		case POLICY_CHECK:
> > +			if (entry->flags & ~(IMA_FUNC | IMA_MASK | IMA_FSMAGIC |
> > +					     IMA_UID | IMA_FOWNER | IMA_FSUUID |
> > +					     IMA_INMASK | IMA_EUID | IMA_PCR |
> > +					     IMA_FSNAME | IMA_DIGSIG_REQUIRED |
> > +					     IMA_PERMIT_DIRECTIO |
> > +					     IMA_MODSIG_ALLOWED |
> > +					     IMA_CHECK_BLACKLIST))
> > +				return false;
> > +
> >   			break;
> >   		case KEXEC_CMDLINE:
> >   			if (entry->action & ~(MEASURE | DONT_MEASURE))
> > @@ -1027,7 +1036,8 @@ static bool ima_validate_rule(struct ima_rule_entry *entry)
> >   		default:
> >   			return false;
> >   		}
> > -	}
> > +	} else if (entry->flags & IMA_KEYRINGS)
> > +		return false;
> >   	return true;
> >   }
> > @@ -1209,7 +1219,6 @@ static int ima_parse_rule(char *rule, struct ima_rule_entry *entry)
> >   			keyrings_len = strlen(args[0].from) + 1;
> >   			if ((entry->keyrings) ||
> > -			    (entry->func != KEY_CHECK) ||
> >   			    (keyrings_len < 2)) {
> >   				result = -EINVAL;
> >   				break;
> >