linux-kernel - [PATCH 3.4 4/8] zram: protect sysfs handler from invalid memory access

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Date:	Thu, 12 Jun 2014 16:22:51 -0700
From:	Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:	linux-kernel@...r.kernel.org
Cc:	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	stable@...r.kernel.org, Jiang Liu <jiang.liu@...wei.com>,
	Minchan Kim <minchan@...nel.org>,
	Ben Hutchings <ben@...adent.org.uk>,
	Yijing Wang <wangyijing@...wei.com>
Subject: [PATCH 3.4 4/8] zram: protect sysfs handler from invalid memory access

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

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

From: Jiang Liu <liuj97@...il.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@...wei.com>
Acked-by: Minchan Kim <minchan@...nel.org>
[bwh: Backported to 3.2: adjust context]
Signed-off-by: Ben Hutchings <ben@...adent.org.uk>
[wyj: Backported to 3.4: adjust context]
Signed-off-by: Yijing Wang <wangyijing@...wei.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
---
 drivers/staging/zram/zram_sysfs.c |    2 ++
 1 file changed, 2 insertions(+)

--- a/drivers/staging/zram/zram_sysfs.c
+++ b/drivers/staging/zram/zram_sysfs.c
@@ -188,10 +188,12 @@ static ssize_t mem_used_total_show(struc
 	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);
 }


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