linux-kernel - [PATCHv2] zram: restrict add/remove attributes to root only

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Date:   Sun,  4 Dec 2016 21:44:13 +0900
From:   Sergey Senozhatsky <sergey.senozhatsky@...il.com>
To:     Andrew Morton <akpm@...ux-foundation.org>
Cc:     Greg KH <gregkh@...uxfoundation.org>,
        Minchan Kim <minchan@...nel.org>,
        Steven Allen <steven@...balien.com>,
        linux-kernel@...r.kernel.org, stable@...r.kernel.org,
        Sergey Senozhatsky <sergey.senozhatsky.work@...il.com>,
        Sergey Senozhatsky <sergey.senozhatsky@...il.com>
Subject: [PATCHv2] 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.

Fixes: 6566d1a32bf72 ("zram: add dynamic device add/remove functionality")
Reported-by: Steven Allen <steven@...balien.com>
Cc: <stable@...r.kernel.org>    [4.2+]
Signed-off-by: Sergey Senozhatsky <sergey.senozhatsky@...il.com>
---
 drivers/block/zram/zram_drv.c | 11 +++++++++--
 1 file changed, 9 insertions(+), 2 deletions(-)

diff --git a/drivers/block/zram/zram_drv.c b/drivers/block/zram/zram_drv.c
index 5163c8f..3a0576f 100644
--- a/drivers/block/zram/zram_drv.c
+++ b/drivers/block/zram/zram_drv.c
@@ -1413,9 +1413,16 @@ 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 sence 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_WO(hot_remove),
+	__ATTR(hot_add, 0400, hot_add_show, NULL),
+	__ATTR(hot_remove, 0200, NULL, hot_remove_store),
 	__ATTR_NULL,
 };
 
-- 
2.10.2