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

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Date:   Sat, 27 Jun 2020 16:49:46 -0700
From:   Lakshmi Ramasubramanian <nramas@...ux.microsoft.com>
To:     Tyler Hicks <tyhicks@...ux.microsoft.com>,
        Mimi Zohar <zohar@...ux.ibm.com>,
        Dmitry Kasatkin <dmitry.kasatkin@...il.com>
Cc:     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 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.

  -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;
>