zram: restrict add/remove attributes to root only

zram hot_add sysfs attribute is a very 'special' attribute - reading
from it creates a new uninitialized zram device.  This file, by a
mistake, can be read by a 'normal' user at the moment, while only root
must be able to create a new zram device, therefore hot_add attribute
must have S_IRUSR mode, not S_IRUGO.

[[email protected]: s/sence/sense/, reflow comment to use 80 cols]
Fixes: 6566d1a32bf72 ("zram: add dynamic device add/remove functionality")
Link: http://lkml.kernel.org/r/[email protected]
Signed-off-by: Sergey Senozhatsky <[email protected]>
Reported-by: Steven Allen <[email protected]>
Acked-by: Greg Kroah-Hartman <[email protected]>
Cc: Minchan Kim <[email protected]>
Cc: <[email protected]>    [4.2+]
Signed-off-by: Andrew Morton <[email protected]>
Signed-off-by: Linus Torvalds <[email protected]>

1 files changed, 7 insertions, 1 deletions

diff --git a/drivers/block/zram/zram_drv.c b/drivers/block/zram/zram_drv.c
index 5163c8f918cb..5497f7fc44d0 100644
--- a/drivers/block/zram/zram_drv.c
+++ b/drivers/block/zram/zram_drv.c
@@ -1413,8 +1413,14 @@ static ssize_t hot_remove_store(struct class *class,
 	return ret ? ret : count;
 }
 
+/*
+ * NOTE: hot_add attribute is not the usual read-only sysfs attribute. In a
+ * sense that reading from this file does alter the state of your system -- it
+ * creates a new un-initialized zram device and returns back this device's
+ * device_id (or an error code if it fails to create a new device).
+ */
 static struct class_attribute zram_control_class_attrs[] = {
-	__ATTR_RO(hot_add),
+	__ATTR(hot_add, 0400, hot_add_show, NULL),
 	__ATTR_WO(hot_remove),
 	__ATTR_NULL,
 };