linux-kernel - Re: [PATCH v4 2/4] of: overlay: global sysfs enable attribute

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Message-ID: <CAL_Jsq+b8DvZOTxecug+0s4y694jqTTAu9y4kLKHqUn=kvNEfg@mail.gmail.com>
Date:	Tue, 1 Sep 2015 21:43:43 -0500
From:	Rob Herring <robherring2@...il.com>
To:	Pantelis Antoniou <pantelis.antoniou@...sulko.com>,
	Grant Likely <grant.likely@...retlab.ca>
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	Matt Porter <mporter@...sulko.com>,
	Koen Kooi <koen@...inion.thruhere.net>,
	Guenter Roeck <linux@...ck-us.net>,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	"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 v4 2/4] of: overlay: global sysfs enable attribute

On Fri, Jun 12, 2015 at 2:38 PM, Pantelis Antoniou
<pantelis.antoniou@...sulko.com> 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>

I had some questioning whether we want more states than just on/off
like "only add sub-trees", but I've convinced myself it is better to
keep the kill switch simple. So I'm okay with patches 1 and 2 (and the
relevant part of 4 if you want to split it). I think #3 needs to be
part of how we expect userspace to interact with overlays.

Please respin and I will queue at least the kill switch for 4.4 unless
there are further comments.

Rob


> ---
>  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 f17f5ef..37ec858 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)
> @@ -596,5 +634,8 @@ 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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