[PATCH 06/98] zram: protect sysfs handler from invalid memory access

[Luis Henriques]

3.5.7.17 -stable review patch.  If anyone has any objections, please let me know.

------------------

From: Jiang Liu <liuj97 at gmail.com>

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 at huawei.com>
Acked-by: Minchan Kim <minchan at kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh at linuxfoundation.org>
[ luis: backported to 3.5:
  - protect access to zram->mem_pool instead of zram->meta ]
Signed-off-by: Luis Henriques <luis.henriques at canonical.com>
---
 drivers/staging/zram/zram_sysfs.c | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/drivers/staging/zram/zram_sysfs.c b/drivers/staging/zram/zram_sysfs.c
index a7f3771..dbe8907 100644
--- a/drivers/staging/zram/zram_sysfs.c
+++ b/drivers/staging/zram/zram_sysfs.c
@@ -186,10 +186,12 @@ static ssize_t mem_used_total_show(struct device *dev,
 	u64 val = 0;
 	struct zram *zram = dev_to_zram(dev);
 
+	down_read(&zram->init_lock);
 	if (zram->init_done) {
 		val = zs_get_total_size_bytes(zram->mem_pool) +
 			((u64)(zram->stats.pages_expand) << PAGE_SHIFT);
 	}
+	up_read(&zram->init_lock);
 
 	return sprintf(buf, "%llu\n", val);
 }
-- 
1.8.1.2