linux-kernel - Re: [PATCH v3 07/12] ima: Fail rule parsing when appraise

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Date:   Thu, 16 Jul 2020 14:14:50 -0400
From:   Mimi Zohar <zohar@...ux.ibm.com>
To:     Tyler Hicks <tyhicks@...ux.microsoft.com>,
        Dmitry Kasatkin <dmitry.kasatkin@...il.com>
Cc:     James Morris <jmorris@...ei.org>,
        "Serge E . Hallyn" <serge@...lyn.com>,
        Lakshmi Ramasubramanian <nramas@...ux.microsoft.com>,
        Prakhar Srivastava <prsriva02@...il.com>,
        linux-kernel@...r.kernel.org, linux-integrity@...r.kernel.org,
        linux-security-module@...r.kernel.org,
        Nayna Jain <nayna@...ux.ibm.com>
Subject: Re: [PATCH v3 07/12] ima: Fail rule parsing when
 appraise_flag=blacklist is unsupportable

On Thu, 2020-07-09 at 01:19 -0500, Tyler Hicks wrote:
> The "appraise_flag" option is only appropriate for appraise actions
> and its "blacklist" value is only appropriate when
> CONFIG_IMA_APPRAISE_MODSIG is enabled and "appraise_flag=blacklist" is
> only appropriate when "appraise_type=imasig|modsig" is also present.
> Make this clear at policy load so that IMA policy authors don't assume
> that other uses of "appraise_flag=blacklist" are supported.

The code looks correct, but this patch description could be written at
a higher level.  Perhaps it just needs to be prefixed with something
like this:

Verifying that a file hash is not blacklisted is currently only
supported for files with appended signatures (modsig).  In the future,
this might change.  For now, ...

Mimi

> 
> Fixes: 273df864cf74 ("ima: Check against blacklisted hashes for files with modsig")
> Signed-off-by: Tyler Hicks <tyhicks@...ux.microsoft.com>
> Cc: Nayna Jain <nayna@...ux.ibm.com>

> ---
> 
> * v3
>   - New patch
> 
>  security/integrity/ima/ima_policy.c | 13 ++++++++++++-
>  1 file changed, 12 insertions(+), 1 deletion(-)
> 
> diff --git a/security/integrity/ima/ima_policy.c b/security/integrity/ima/ima_policy.c
> index 81da02071d41..9842e2e0bc6d 100644
> --- a/security/integrity/ima/ima_policy.c
> +++ b/security/integrity/ima/ima_policy.c
> @@ -1035,6 +1035,11 @@ static bool ima_validate_rule(struct ima_rule_entry *entry)
>  		return false;
>  	}
>  
> +	/* Ensure that combinations of flags are compatible with each other */
> +	if (entry->flags & IMA_CHECK_BLACKLIST &&
> +	    !(entry->flags & IMA_MODSIG_ALLOWED))
> +		return false;
> +
>  	return true;
>  }
>  
> @@ -1371,8 +1376,14 @@ static int ima_parse_rule(char *rule, struct ima_rule_entry *entry)
>  				result = -EINVAL;
>  			break;
>  		case Opt_appraise_flag:
> +			if (entry->action != APPRAISE) {
> +				result = -EINVAL;
> +				break;
> +			}
> +
>  			ima_log_string(ab, "appraise_flag", args[0].from);
> -			if (strstr(args[0].from, "blacklist"))
> +			if (IS_ENABLED(CONFIG_IMA_APPRAISE_MODSIG) &&
> +			    strstr(args[0].from, "blacklist"))
>  				entry->flags |= IMA_CHECK_BLACKLIST;
>  			break;
>  		case Opt_permit_directio: