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[PATCH v7 2/6] of: overlay: global sysfs enable attribute

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  [PATCH v7 2/6] of: overlay: global sysfs enable attribute Pantelis Antoniou <pantelis.antoniou@konsulko.com> - 2015-10-22 22:00 +0200
    Re: [PATCH v7 2/6] of: overlay: global sysfs enable attribute Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2015-10-22 22:20 +0200
      Re: [PATCH v7 2/6] of: overlay: global sysfs enable attribute Pantelis Antoniou <panto@antoniou-consulting.com> - 2015-10-22 22:40 +0200

#1254139 — [PATCH v7 2/6] of: overlay: global sysfs enable attribute

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

A kernel command line option is provided as well.

Signed-off-by: Pantelis Antoniou <pantelis.antoniou@konsulko.com>
---
 drivers/of/overlay.c | 50 +++++++++++++++++++++++++++++++++++++++++++++++++-
 1 file changed, 49 insertions(+), 1 deletion(-)

diff --git a/drivers/of/overlay.c b/drivers/of/overlay.c
index 12c3e47..91f10ed 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 +56,19 @@ 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 __init of_overlay_disable_setup(char *str __always_unused)
+{
+	atomic_set(&ov_enable, 0);
+	return 1;
+}
+__setup("of_overlay_disable", of_overlay_disable_setup);
+
 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 +351,35 @@ 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 +401,10 @@ 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 +639,8 @@ 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;
 }
-- 
1.7.12

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#1254154

On Thu, Oct 22, 2015 at 10:50:23PM +0300, Pantelis Antoniou wrote:
> A throw once master enable switch to protect against any
> further overlay applications if the administrator desires so.
> 
> A kernel command line option is provided as well.
> 
> Signed-off-by: Pantelis Antoniou <pantelis.antoniou@konsulko.com>
> ---
>  drivers/of/overlay.c | 50 +++++++++++++++++++++++++++++++++++++++++++++++++-
>  1 file changed, 49 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/of/overlay.c b/drivers/of/overlay.c
> index 12c3e47..91f10ed 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 +56,19 @@ 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 __init of_overlay_disable_setup(char *str __always_unused)
> +{
> +	atomic_set(&ov_enable, 0);
> +	return 1;
> +}
> +__setup("of_overlay_disable", of_overlay_disable_setup);
> +
>  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 +351,35 @@ 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));

Minor nit, you never need to care about the size of the buffer for a
sysfs file, if you do, you are doing something wrong.  So this can just
be:
	return sprintf(buf, "%d\n", atomic_read(&ov_enable));


Anyway, nothing worth keeping this from being merged:

Acked-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

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#1254167

Hi Greg,

> On Oct 22, 2015, at 23:19 , Greg Kroah-Hartman <gregkh@linuxfoundation.org> wrote:
> 
> On Thu, Oct 22, 2015 at 10:50:23PM +0300, Pantelis Antoniou wrote:
>> A throw once master enable switch to protect against any
>> further overlay applications if the administrator desires so.
>> 
>> A kernel command line option is provided as well.
>> 
>> Signed-off-by: Pantelis Antoniou <pantelis.antoniou@konsulko.com>
>> ---
>> drivers/of/overlay.c | 50 +++++++++++++++++++++++++++++++++++++++++++++++++-
>> 1 file changed, 49 insertions(+), 1 deletion(-)
>> 
>> diff --git a/drivers/of/overlay.c b/drivers/of/overlay.c
>> index 12c3e47..91f10ed 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 +56,19 @@ 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 __init of_overlay_disable_setup(char *str __always_unused)
>> +{
>> +	atomic_set(&ov_enable, 0);
>> +	return 1;
>> +}
>> +__setup("of_overlay_disable", of_overlay_disable_setup);
>> +
>> 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 +351,35 @@ 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));
> 
> Minor nit, you never need to care about the size of the buffer for a
> sysfs file, if you do, you are doing something wrong.  So this can just
> be:
> 	return sprintf(buf, "%d\n", atomic_read(&ov_enable));
> 
> 

Nice to know; I have a ingrained habit to avoid standard sprintf, so..

> Anyway, nothing worth keeping this from being merged:
> 


Thanks!

> Acked-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
> 

Regards

— Pantelis

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