linux-kernel - Re: [PATCH 05/12] ima: Fail rule parsing when buffer hook functions have an invalid action

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Date:   Thu, 25 Jun 2020 17:51:54 -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
Subject: Re: [PATCH 05/12] ima: Fail rule parsing when buffer hook functions
 have an invalid action

On Mon, 2020-06-22 at 19:32 -0500, Tyler Hicks wrote:
> Buffer based hook functions, such as KEXEC_CMDLINE and KEY_CHECK, can
> only measure. The process_buffer_measurement() function quietly ignores
> all actions except measure so make this behavior clear at the time of
> policy load.
> 
> The parsing of the keyrings conditional had a check to ensure that it
> was only specified with measure actions but the check should be on the
> hook function and not the keyrings conditional since
> "appraise func=KEY_CHECK" is not a valid rule.
> 
> Fixes: b0935123a183 ("IMA: Define a new hook to measure the kexec boot command line arguments")
> Fixes: 5808611cccb2 ("IMA: Add KEY_CHECK func to measure keys")
> Signed-off-by: Tyler Hicks <tyhicks@...ux.microsoft.com>
> ---
>  security/integrity/ima/ima_policy.c | 36 +++++++++++++++++++++++++++--
>  1 file changed, 34 insertions(+), 2 deletions(-)
> 
> diff --git a/security/integrity/ima/ima_policy.c b/security/integrity/ima/ima_policy.c
> index ee5152ecd3d9..ecc234b956a2 100644
> --- a/security/integrity/ima/ima_policy.c
> +++ b/security/integrity/ima/ima_policy.c
> @@ -979,6 +979,39 @@ static void check_template_modsig(const struct ima_template_desc *template)
>  #undef MSG
>  }
>  
> +static bool ima_validate_rule(struct ima_rule_entry *entry)
> +{
> +	if (entry->action == UNKNOWN)
> +		return false;
> +
> +	if (entry->flags & IMA_FUNC) {
> +		switch (entry->func) {
> +		case NONE:
> +		case FILE_CHECK:
> +		case MMAP_CHECK:
> +		case BPRM_CHECK:
> +		case CREDS_CHECK:
> +		case POST_SETATTR:
> +		case MODULE_CHECK:
> +		case FIRMWARE_CHECK:
> +		case KEXEC_KERNEL_CHECK:
> +		case KEXEC_INITRAMFS_CHECK:
> +		case POLICY_CHECK:
> +			break;
> +		case KEXEC_CMDLINE:
> +		case KEY_CHECK:
> +			if (entry->action & ~(MEASURE | DONT_MEASURE))
> +				return false;
> +
> +			break;
> +		default:
> +			return false;
> +		}
> +	}
> +
> +	return true;
> +}
> +

Good idea.  There are a couple of other examples that could be cleaned
up as well.  For example, for performance reasons
"appraise_flag=check_blacklist" is limited to files with appended
signatures, like kernel modules and the kexec kernel image
(OpenPower).

Mimi