[PATCH V37 19/29] Lock down module params that specify hardware parameters (eg. ioport)

[Matthew Garrett]

From: David Howells <dhowe...@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 <gno...@lxorguk.ukuu.org.uk>
Signed-off-by: David Howells <dhowe...@redhat.com>
Signed-off-by: Matthew Garrett <mj...@google.com>
Reviewed-by: Kees Cook <keesc...@chromium.org>
Cc: Jessica Yu <j...@kernel.org>
---
 include/linux/security.h     |  1 +
 kernel/params.c              | 28 +++++++++++++++++++++++-----
 security/lockdown/lockdown.c |  1 +
 3 files changed, 25 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..f2779a76d39a 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 +97,20 @@ 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_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 +140,10 @@ 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;
                }
@@ -541,6 +551,12 @@ 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,
@@ -553,8 +569,10 @@ 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 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