Re: [PATCH v6 2/4] of: overlay: global sysfs enable attribute

On Tue, Oct 20, 2015 at 4:06 PM, Greg Kroah-Hartman
[off-list ref] wrote:

On Tue, Oct 20, 2015 at 10:13:15PM +0300, Pantelis Antoniou wrote:

quoted

A throw once master enable switch to protect against any
further overlay applications if the administrator desires so.

Signed-off-by: Pantelis Antoniou <pantelis.antoniou-OWPKS81ov/FWk0Htik3J/w@public.gmane.org>
---
 drivers/of/overlay.c | 43 ++++++++++++++++++++++++++++++++++++++++++-
 1 file changed, 42 insertions(+), 1 deletion(-)

diff --git a/drivers/of/overlay.c b/drivers/of/overlay.c
index 12c3e47..067404e 100644
--- a/drivers/of/overlay.c
+++ b/drivers/of/overlay.c

@@ -21,6 +21,7 @@
 #include <linux/err.h>
 #include <linux/idr.h>
 #include <linux/sysfs.h>
+#include <linux/atomic.h>

 #include "of_private.h"

@@ -55,8 +56,12 @@ struct of_overlay {
      struct kobject kobj;
 };

+/* master enable switch; once set to 0 can't be re-enabled */
+static atomic_t ov_enable = ATOMIC_INIT(1);
+
 static int of_overlay_apply_one(struct of_overlay *ov,
              struct device_node *target, const struct device_node *overlay);
+static int overlay_removal_is_ok(struct of_overlay *ov);

 static int of_overlay_apply_single_property(struct of_overlay *ov,
              struct device_node *target, struct property *prop)

@@ -339,6 +344,35 @@ void of_overlay_release(struct kobject *kobj)
      kfree(ov);
 }

+static ssize_t enable_show(struct kobject *kobj,
+             struct kobj_attribute *attr, char *buf)
+{
+     return snprintf(buf, PAGE_SIZE, "%d\n", atomic_read(&ov_enable));
+}
+
+static ssize_t enable_store(struct kobject *kobj,
+             struct kobj_attribute *attr, const char *buf, size_t count)
+{
+     int ret;
+     bool new_enable;
+
+     ret = strtobool(buf, &new_enable);
+     if (ret != 0)
+             return ret;
+     /* if we've disabled it, no going back */
+     if (atomic_read(&ov_enable) == 0)
+             return -EPERM;
+     atomic_set(&ov_enable, (int)new_enable);
+     return count;
+}
+
+static struct kobj_attribute enable_attr = __ATTR_RW(enable);
+
+static const struct attribute *overlay_global_attrs[] = {
+     &enable_attr.attr,
+     NULL
+};
+
 static struct kobj_type of_overlay_ktype = {
      .release = of_overlay_release,
 };

@@ -360,6 +394,10 @@ int of_overlay_create(struct device_node *tree)
      struct of_overlay *ov;
      int err, id;

+     /* administratively disabled */
+     if (!atomic_read(&ov_enable))
+             return -EPERM;
+
      /* allocate the overlay structure */
      ov = kzalloc(sizeof(*ov), GFP_KERNEL);
      if (ov == NULL)

@@ -594,5 +632,8 @@ int of_overlay_init(void)
      if (!ov_kset)
              return -ENOMEM;

-     return 0;
+     rc = sysfs_create_files(&ov_kset->kobj, overlay_global_attrs);
+     WARN(rc, "%s: error adding global attributes\n", __func__);
+
+     return rc;
 }

Shouldn't this also be allowed to be overridden as a boot and build time
parameter to prevent any races on systems that don't want this?

Build time is already there to disable overlays. A command line option
would be good though.

Rob
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