[RFC PATCH v1 2/8] zram: avoid invalid memory access in zram_exit()

[Jiang Liu <liuj97@gmail.com>]

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.

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

Signed-off-by: Jiang Liu <jiang.liu@huawei.com>
---
 drivers/staging/zram/zram_drv.c | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/drivers/staging/zram/zram_drv.c b/drivers/staging/zram/zram_drv.c
index e34e3fe..ee6b67d 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");
-- 
1.8.1.2