From: Jiang Liu <liuj97@gmail.com>
Date: Thu, 6 Jun 2013 16:07:22 +0000 (+0800)
Subject: zram: avoid invalid memory access in zram_exit()
X-Git-Tag: firefly_0821_release~6453^2~1176
X-Git-Url: http://demsky.eecs.uci.edu/git/?a=commitdiff_plain;h=b74c38d5b6af46482480f6f8b83633e2971a0ed8;p=firefly-linux-kernel-4.4.55.git

zram: avoid invalid memory access in zram_exit()

commit 6030ea9b35971a4200062f010341ab832e878ac9 upstream.

Memory for zram->disk object may have already been freed after returning
from destroy_device(zram), then it's unsafe for zram_reset_device(zram)
to access zram->disk again.

We can't solve this bug by flipping the order of destroy_device(zram)
and zram_reset_device(zram), that will cause deadlock issues to the
zram sysfs handler.

So fix it by holding an extra reference to zram->disk before calling
destroy_device(zram).

Signed-off-by: Jiang Liu <jiang.liu@huawei.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---

diff --git a/drivers/staging/zram/zram_drv.c b/drivers/staging/zram/zram_drv.c
index e34e3fe0ae2e..ee6b67d77340 100644
--- a/drivers/staging/zram/zram_drv.c
+++ b/drivers/staging/zram/zram_drv.c
@@ -727,8 +727,10 @@ static void __exit zram_exit(void)
 	for (i = 0; i < num_devices; i++) {
 		zram = &zram_devices[i];
 
+		get_disk(zram->disk);
 		destroy_device(zram);
 		zram_reset_device(zram);
+		put_disk(zram->disk);
 	}
 
 	unregister_blkdev(zram_major, "zram");