zram: avoid invalid memory access in zram_exit()

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>
Cc: stable@vger.kernel.org
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 d628bd30113cf9329e3a0105190a76f8efa5124e..9057520c0e4039cf9a55fdd8c28f2931dec0fb4d 100644 (file)
--- 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");