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From:   Daniel Axtens <dja@axtens.net>
To:     Matthew Garrett <matthewgarrett@google.com>, jmorris@namei.org
Cc:     linux-security-module@vger.kernel.org,
        linux-kernel@vger.kernel.org, linux-api@vger.kernel.org,
        David Howells <dhowells@redhat.com>,
        Alan Cox <gnomes@lxorguk.ukuu.org.uk>,
        Matthew Garrett <mjg59@google.com>
Subject: Re: [PATCH V34 19/29] Lock down module params that specify hardware parameters (eg. ioport)
In-Reply-To: <20190622000358.19895-20-matthewgarrett@google.com>
References: <20190622000358.19895-1-matthewgarrett@google.com> <20190622000358.19895-20-matthewgarrett@google.com>
Date:   Thu, 27 Jun 2019 11:49:30 +1000
Message-ID: <87ef3f3ihh.fsf@dja-thinkpad.axtens.net>
MIME-Version: 1.0
Content-Type: text/plain
Sender: linux-kernel-owner@vger.kernel.org
Precedence: bulk

Matthew Garrett <matthewgarrett@google.com> writes:

> From: David Howells <dhowells@redhat.com>
>
> Provided an annotation for module parameters that specify hardware
> parameters (such as io ports, iomem addresses, irqs, dma channels, fixed
> dma buffers and other types).
>
> Suggested-by: Alan Cox <gnomes@lxorguk.ukuu.org.uk>
> Signed-off-by: David Howells <dhowells@redhat.com>
> Signed-off-by: Matthew Garrett <mjg59@google.com>
> ---
>  include/linux/security.h     |  1 +
>  kernel/params.c              | 27 ++++++++++++++++++++++-----
>  security/lockdown/lockdown.c |  1 +
>  3 files changed, 24 insertions(+), 5 deletions(-)
>
> diff --git a/include/linux/security.h b/include/linux/security.h
> index 61e3f4a62d16..88064d7f6827 100644
> --- a/include/linux/security.h
> +++ b/include/linux/security.h
> @@ -92,6 +92,7 @@ enum lockdown_reason {
>  	LOCKDOWN_ACPI_TABLES,
>  	LOCKDOWN_PCMCIA_CIS,
>  	LOCKDOWN_TIOCSSERIAL,
> +	LOCKDOWN_MODULE_PARAMETERS,
>  	LOCKDOWN_INTEGRITY_MAX,
>  	LOCKDOWN_CONFIDENTIALITY_MAX,
>  };
> diff --git a/kernel/params.c b/kernel/params.c
> index ce89f757e6da..f94fe79e331d 100644
> --- a/kernel/params.c
> +++ b/kernel/params.c
> @@ -24,6 +24,7 @@
>  #include <linux/err.h>
>  #include <linux/slab.h>
>  #include <linux/ctype.h>
> +#include <linux/security.h>
>  
>  #ifdef CONFIG_SYSFS
>  /* Protects all built-in parameters, modules use their own param_lock */
> @@ -108,13 +109,19 @@ bool parameq(const char *a, const char *b)
>  	return parameqn(a, b, strlen(a)+1);
>  }
>  
> -static void param_check_unsafe(const struct kernel_param *kp)
> +static bool param_check_unsafe(const struct kernel_param *kp,
> +			       const char *doing)
>  {
>  	if (kp->flags & KERNEL_PARAM_FL_UNSAFE) {
>  		pr_notice("Setting dangerous option %s - tainting kernel\n",
>  			  kp->name);
>  		add_taint(TAINT_USER, LOCKDEP_STILL_OK);
>  	}
> +
> +	if (kp->flags & KERNEL_PARAM_FL_HWPARAM &&
> +	    security_locked_down(LOCKDOWN_MODULE_PARAMETERS))
> +		return false;
> +	return true;
>  }

Should this test occur before tainting the kernel?

Regards,
Daniel

>  
>  static int parse_one(char *param,
> @@ -144,8 +151,10 @@ static int parse_one(char *param,
>  			pr_debug("handling %s with %p\n", param,
>  				params[i].ops->set);
>  			kernel_param_lock(params[i].mod);
> -			param_check_unsafe(&params[i]);
> -			err = params[i].ops->set(val, &params[i]);
> +			if (param_check_unsafe(&params[i], doing))
> +				err = params[i].ops->set(val, &params[i]);
> +			else
> +				err = -EPERM;
>  			kernel_param_unlock(params[i].mod);
>  			return err;
>  		}
> @@ -553,6 +562,12 @@ static ssize_t param_attr_show(struct module_attribute *mattr,
>  	return count;
>  }
>  
> +#ifdef CONFIG_MODULES
> +#define mod_name(mod) (mod)->name
> +#else
> +#define mod_name(mod) "unknown"
> +#endif
> +
>  /* sysfs always hands a nul-terminated string in buf.  We rely on that. */
>  static ssize_t param_attr_store(struct module_attribute *mattr,
>  				struct module_kobject *mk,
> @@ -565,8 +580,10 @@ static ssize_t param_attr_store(struct module_attribute *mattr,
>  		return -EPERM;
>  
>  	kernel_param_lock(mk->mod);
> -	param_check_unsafe(attribute->param);
> -	err = attribute->param->ops->set(buf, attribute->param);
> +	if (param_check_unsafe(attribute->param, mod_name(mk->mod)))
> +		err = attribute->param->ops->set(buf, attribute->param);
> +	else
> +		err = -EPERM;
>  	kernel_param_unlock(mk->mod);
>  	if (!err)
>  		return len;
> diff --git a/security/lockdown/lockdown.c b/security/lockdown/lockdown.c
> index c89046dc2155..d03c4c296af7 100644
> --- a/security/lockdown/lockdown.c
> +++ b/security/lockdown/lockdown.c
> @@ -28,6 +28,7 @@ static char *lockdown_reasons[LOCKDOWN_CONFIDENTIALITY_MAX+1] = {
>  	[LOCKDOWN_ACPI_TABLES] = "modified ACPI tables",
>  	[LOCKDOWN_PCMCIA_CIS] = "direct PCMCIA CIS storage",
>  	[LOCKDOWN_TIOCSSERIAL] = "reconfiguration of serial port IO",
> +	[LOCKDOWN_MODULE_PARAMETERS] = "unsafe module parameters",
>  	[LOCKDOWN_INTEGRITY_MAX] = "integrity",
>  	[LOCKDOWN_CONFIDENTIALITY_MAX] = "confidentiality",
>  };
> -- 
> 2.22.0.410.gd8fdbe21b5-goog