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

[Pantelis Antoniou <pantelis.antoniou@konsulko.com>]

Hi Rob,

> On Oct 21, 2015, at 00:50 , Rob Herring <robherring2@gmail.com> wrote:
> 
> On Tue, Oct 20, 2015 at 4:06 PM, Greg Kroah-Hartman
> <gregkh@linuxfoundation.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@konsulko.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.
> 

No problemo. I’ll include it in the next version to go out today.

> Rob

Regards

— Pantelis