On Fri, Apr 24, 2015 at 12:45:42PM +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@xxxxxxxxxxxx>
> ---
> drivers/of/overlay.c | 45 ++++++++++++++++++++++++++++++++++++++++++++-
> 1 file changed, 44 insertions(+), 1 deletion(-)
>
> diff --git a/drivers/of/overlay.c b/drivers/of/overlay.c
> index f17f5ef..c335809 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 +344,37 @@ 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;
> + long new_enable;
> +
> + ret = kstrtol(buf, 10, &new_enable);
> + if (ret != 0)
> + return ret;
> + if ((unsigned long)new_enable > 1)
> + return -EINVAL;
> + /* 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
> +};
Why not make this an attribute group and then attach it to the kobj_type
to create the files in a race-free manner?
> +
> static struct kobj_type of_overlay_ktype = {
> .release = of_overlay_release,
> };
> @@ -360,6 +396,10 @@ 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 +636,8 @@ 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__);
What can a user do with this warning message? If nothing, then don't
print it out, right?
You are creating sysfs files _after_ the kobject has been announced to
userspace, causing nasty race conditions. Please don't do that.
thanks,
greg k-h
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