linux-kernel - Re: [PATCH v2 05/11] ima: Fail rule parsing when the KEXEC_CMDLINE hook is combined with an invalid cond

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Date:   Sat, 27 Jun 2020 16:40:23 -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 05/11] ima: Fail rule parsing when the KEXEC_CMDLINE
 hook is combined with an invalid cond

On 6/26/20 3:38 PM, Tyler Hicks wrote:
> The KEXEC_CMDLINE hook function only supports the pcr conditional. Make
> this clear at policy load so that IMA policy authors don't assume that
> other conditionals are supported.
> 
> Since KEXEC_CMDLINE's inception, ima_match_rules() has always returned
> true on any loaded KEXEC_CMDLINE rule without any consideration for
> other conditionals present in the rule. Make it clear that pcr is the
> only supported KEXEC_CMDLINE conditional by returning an error during
> policy load.
> 
> An example of why this is a problem can be explained with the following
> rule:
> 
>   dont_measure func=KEXEC_CMDLINE obj_type=foo_t
> 
> An IMA policy author would have assumed that rule is valid because the
> parser accepted it but the result was that measurements for all
> KEXEC_CMDLINE operations would be disabled.
> 
> Fixes: b0935123a183 ("IMA: Define a new hook to measure the kexec boot command line arguments")
> Signed-off-by: Tyler Hicks <tyhicks@...ux.microsoft.com>
> Reviewed-by: Mimi Zohar <zohar@...ux.ibm.com>
> ---
> 
> * v2
>    - Added Mimi's Reviewed-by
> 
>   security/integrity/ima/ima_policy.c | 21 +++++++++++++++++++++
>   1 file changed, 21 insertions(+)
> 
> diff --git a/security/integrity/ima/ima_policy.c b/security/integrity/ima/ima_policy.c
> index 166124d67774..676d5557af1a 100644
> --- a/security/integrity/ima/ima_policy.c
> +++ b/security/integrity/ima/ima_policy.c
> @@ -343,6 +343,17 @@ static int ima_lsm_update_rule(struct ima_rule_entry *entry)
>   	return 0;
>   }
>   
> +static bool ima_rule_contains_lsm_cond(struct ima_rule_entry *entry)
> +{
> +	int i;
> +
> +	for (i = 0; i < MAX_LSM_RULES; i++)
> +		if (entry->lsm[i].args_p)
> +			return true;
> +
> +	return false;
> +}
> +
>   /*
>    * The LSM policy can be reloaded, leaving the IMA LSM based rules referring
>    * to the old, stale LSM policy.  Update the IMA LSM based rules to reflect
> @@ -993,6 +1004,16 @@ static bool ima_validate_rule(struct ima_rule_entry *entry)
>   		case POLICY_CHECK:
>   			break;
>   		case KEXEC_CMDLINE:
> +			if (entry->action & ~(MEASURE | DONT_MEASURE))
> +				return false;
> +
> +			if (entry->flags & ~(IMA_FUNC | IMA_PCR))
> +				return false;
> +
> +			if (ima_rule_contains_lsm_cond(entry))
> +				return false;
> +
> +			break;
>   		case KEY_CHECK:
>   			if (entry->action & ~(MEASURE | DONT_MEASURE))
>   				return false;
> 

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