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

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Date:	Tue, 20 Oct 2015 16:50:27 -0500
From:	Rob Herring <robherring2@...il.com>
To:	Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Cc:	Pantelis Antoniou <pantelis.antoniou@...sulko.com>,
	Frank Rowand <frowand.list@...il.com>,
	Matt Porter <mporter@...sulko.com>,
	Koen Kooi <koen@...inion.thruhere.net>,
	Guenter Roeck <linux@...ck-us.net>,
	"devicetree@...r.kernel.org" <devicetree@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"linux-api@...r.kernel.org" <linux-api@...r.kernel.org>,
	Pantelis Antoniou <panto@...oniou-consulting.com>
Subject: Re: [PATCH v6 2/4] of: overlay: global sysfs enable attribute

On Tue, Oct 20, 2015 at 4:06 PM, Greg Kroah-Hartman
<gregkh@...uxfoundation.org> wrote:
> On Tue, Oct 20, 2015 at 10:13:15PM +0300, Pantelis Antoniou wrote:
>> 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@...sulko.com>
>> ---
>>  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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