zram: protect sysfs handler from invalid memory access

Use zram->init_lock to protect access to zram->meta, otherwise it
may cause invalid memory access if zram->meta has been freed by
zram_reset_device().

This issue may be triggered by:
Thread 1:
while true; do cat mem_used_total; done
Thread 2:
while true; do echo 8M > disksize; echo 1 > reset; done

Signed-off-by: Jiang Liu <jiang.liu@huawei.com>
Acked-by: Minchan Kim <minchan@kernel.org>
Cc: stable@vger.kernel.org
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

diff --git a/drivers/staging/zram/zram_sysfs.c b/drivers/staging/zram/zram_sysfs.c
index e6a929d452f72cda5b9953e1b9b0a1b3c15cb13d..dc76a3dba1b8d918f42d59cdc1cf1c6ae39de79d 100644 (file)
--- a/drivers/staging/zram/zram_sysfs.c
+++ b/drivers/staging/zram/zram_sysfs.c
@@ -188,8 +188,10 @@ static ssize_t mem_used_total_show(struct device *dev,
        struct zram *zram = dev_to_zram(dev);
        struct zram_meta *meta = zram->meta;
 
+       down_read(&zram->init_lock);
        if (zram->init_done)
                val = zs_get_total_size_bytes(meta->mem_pool);
+       up_read(&zram->init_lock);
 
        return sprintf(buf, "%llu\n", val);
 }