Re: [PATCH V34 19/29] Lock down module params that specify hardware parameters (eg. ioport)

Daniel Axtens
2019-06-27T01:49:40Z

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