Implement a throw once master enable switch to protect against any
further overlay applications if the administrator desires so.
Signed-off-by: Pantelis Antoniou <pantelis.anton...@konsulko.com>
---
drivers/of/overlay.c | 66 +++++++++++++++++++++++++++++++++++++++++++++++++++-
1 file changed, 65 insertions(+), 1 deletion(-)
diff --git a/drivers/of/overlay.c b/drivers/of/overlay.c
index f17f5ef..6688797 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"
@@ -55,6 +56,9 @@ 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);
@@ -345,6 +349,60 @@ static struct kobj_type of_overlay_ktype = {
static struct kset *ov_kset;
+static ssize_t enable_read(struct file *filp, struct kobject *kobj,
+ struct bin_attribute *bin_attr, char *buf,
+ loff_t offset, size_t count)
+{
+ char tbuf[3];
+
+ if (offset < 0)
+ return -EINVAL;
+
+ if (offset >= sizeof(tbuf))
+ return 0;
+
+ if (count > sizeof(tbuf) - offset)
+ count = sizeof(tbuf) - offset;
+
+ /* fill in temp */
+ tbuf[0] = '0' + atomic_read(&ov_enable);
+ tbuf[1] = '\n';
+ tbuf[2] = '\0';
+
+ /* copy to buffer */
+ memcpy(buf, tbuf + offset, count);
+
+ return count;
+}
+
+static ssize_t enable_write(struct file *filp, struct kobject *kobj,
+ struct bin_attribute *bin_attr, char *buf,
+ loff_t off, size_t count)
+{
+ int new_enable;
+
+ if (off != 0 || (buf[0] != '0' && buf[1] != '1'))
+ return -EINVAL;
+
+ new_enable = buf[0] - '0';
+ if (new_enable != 0 && new_enable != 1)
+ return -EINVAL;
+
+ /* NOP for same value */
+ if (new_enable == atomic_read(&ov_enable))
+ return count;
+
+ /* if we've disabled it, no going back */
+ if (atomic_read(&ov_enable) == 0)
+ return -EPERM;
+
+ atomic_set(&ov_enable, new_enable);
+ return count;
+}
+
+/* just a single char + '\n' + '\0' */
+static BIN_ATTR_RW(enable, 3);
+
/**
* of_overlay_create() - Create and apply an overlay
* @tree: Device node containing all the overlays
@@ -360,6 +418,10 @@ 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 +658,7 @@ int of_overlay_init(void)
if (!ov_kset)
return -ENOMEM;
- return 0;
+ rc = sysfs_create_bin_file(&ov_kset->kobj, &bin_attr_enable);
+ WARN(rc, "%s: error adding enable attribute\n", __func__);
+ return rc;
}
--
1.7.12
--
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