Re: [PATCH V38 19/29] Lock down module params that specify hardware parameters (eg. ioport)

[Jessica Yu <jeyu@xxxxxxxxxx>]

+++ Matthew Garrett [07/08/19 17:07 -0700]:
> From: David Howells <dhowells@xxxxxxxxxx>
>
> 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@xxxxxxxxxxxxxxxxxxx>
> Signed-off-by: David Howells <dhowells@xxxxxxxxxx>
> Signed-off-by: Matthew Garrett <mjg59@xxxxxxxxxx>
> Reviewed-by: Kees Cook <keescook@xxxxxxxxxxxx>
> Cc: Jessica Yu <jeyu@xxxxxxxxxx>
> ---
> 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 8f7048395114..43fa3486522b 100644
> --- a/include/linux/security.h
> +++ b/include/linux/security.h
> @@ -113,6 +113,7 @@ 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 cf448785d058..35f138fce762 100644
> --- a/kernel/params.c
> +++ b/kernel/params.c
> @@ -12,6 +12,7 @@
> #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 */
> @@ -96,13 +97,19 @@ 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)
> {
> +	if (kp->flags & KERNEL_PARAM_FL_HWPARAM &&
> +	    security_locked_down(LOCKDOWN_MODULE_PARAMETERS))
> +		return false;
> +
> 	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);
> 	}
> +
> +	return true;
> }
>
> static int parse_one(char *param,
> @@ -132,8 +139,10 @@ 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]))
> +				err = params[i].ops->set(val, &params[i]);
> +			else
> +				err = -EPERM;
> 			kernel_param_unlock(params[i].mod);
> 			return err;
> 		}
> @@ -541,6 +550,12 @@ 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
> +

Hm, I don't think mod_name is used anywhere?

But other than that:

Acked-by: Jessica Yu <jeyu@xxxxxxxxxx>

Thanks!

Jessica

> /* 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,
> @@ -553,8 +568,10 @@ 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))
> +		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 00a3a6438dd2..5177938cfa0d 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] = "modifying 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",
> };
> --
> 2.22.0.770.g0f2c4a37fd-goog