linux-kernel - Re: [PATCH v4 5/8] ima: based on policy require signed firmware (sysfs fallback)

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Date:   Fri, 1 Jun 2018 20:21:07 +0200
From:   "Luis R. Rodriguez" <mcgrof@...nel.org>
To:     Mimi Zohar <zohar@...ux.vnet.ibm.com>
Cc:     linux-integrity@...r.kernel.org,
        linux-security-module@...r.kernel.org,
        linux-kernel@...r.kernel.org, David Howells <dhowells@...hat.com>,
        "Luis R . Rodriguez" <mcgrof@...nel.org>,
        Eric Biederman <ebiederm@...ssion.com>,
        kexec@...ts.infradead.org, Andres Rodriguez <andresx7@...il.com>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Ard Biesheuvel <ard.biesheuvel@...aro.org>,
        Matthew Garrett <mjg59@...gle.com>
Subject: Re: [PATCH v4 5/8] ima: based on policy require signed firmware
 (sysfs fallback)

On Tue, May 29, 2018 at 02:01:57PM -0400, Mimi Zohar wrote:
> Luis, is the security_kernel_post_read_file LSM hook in
> firmware_loading_store() still needed after this patch?  Should it be
> calling security_kernel_load_data() instead?

That's up to Kees to decide as he added that hook, and knows
what LSMs may be doing with it. From my perspective it is confusing
to have that hook there so I think it could be removed now.

Kees?

  Luis

> 
> ---
> 
> With an IMA policy requiring signed firmware, this patch prevents
> the sysfs fallback method of loading firmware.
> 
> Signed-off-by: Mimi Zohar <zohar@...ux.vnet.ibm.com>
> Cc: Luis R. Rodriguez <mcgrof@...e.com>
> Cc: David Howells <dhowells@...hat.com>
> Cc: Matthew Garrett <mjg59@...gle.com>
> ---
>  security/integrity/ima/ima_main.c | 10 +++++++++-
>  1 file changed, 9 insertions(+), 1 deletion(-)
> 
> diff --git a/security/integrity/ima/ima_main.c b/security/integrity/ima/ima_main.c
> index a565d46084c2..4a87f78098c8 100644
> --- a/security/integrity/ima/ima_main.c
> +++ b/security/integrity/ima/ima_main.c
> @@ -475,8 +475,10 @@ int ima_post_read_file(struct file *file, void *buf, loff_t size,
>  
>  	if (!file && read_id == READING_FIRMWARE) {
>  		if ((ima_appraise & IMA_APPRAISE_FIRMWARE) &&
> -		    (ima_appraise & IMA_APPRAISE_ENFORCE))
> +		    (ima_appraise & IMA_APPRAISE_ENFORCE)) {
> +			pr_err("Prevent firmware loading_store.\n");
>  			return -EACCES;	/* INTEGRITY_UNKNOWN */
> +		}
>  		return 0;
>  	}
>  
> @@ -520,6 +522,12 @@ int ima_load_data(enum kernel_load_data_id id)
>  			pr_err("impossible to appraise a kernel image without a file descriptor; try using kexec_file_load syscall.\n");
>  			return -EACCES;	/* INTEGRITY_UNKNOWN */
>  		}
> +		break;
> +	case LOADING_FIRMWARE:
> +		if (ima_appraise & IMA_APPRAISE_FIRMWARE) {
> +			pr_err("Prevent firmware sysfs fallback loading.\n");
> +			return -EACCES;	/* INTEGRITY_UNKNOWN */
> +		}
>  	default:
>  		break;
>  	}
> -- 
> 2.7.5
> 
> 

-- 
Do not panic