From: Jiang Liu <liuj97@gmail.com>
Date: Thu, 6 Jun 2013 16:07:27 +0000 (+0800)
Subject: zram: protect sysfs handler from invalid memory access
X-Git-Tag: firefly_0821_release~6453^2~1171
X-Git-Url: http://demsky.eecs.uci.edu/git/?a=commitdiff_plain;h=c181b464309da49333b85aa9df1eafe2678f1da3;p=firefly-linux-kernel-4.4.55.git

zram: protect sysfs handler from invalid memory access

commit 5863e10b441e7ea4b492f930f1be180a97d026f3 upstream.

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>
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 e6a929d452f7..dc76a3dba1b8 100644
--- 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);
 }