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

From: Jessica Yu
Date: Thu Aug 08 2019 - 07:12:54 EST

+++ 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