[ 065/102] zram: protect sysfs handler from invalid memory access

[Greg Kroah-Hartman]

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

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

From: Jiang Liu <liuj97@xxxxxxxxx>

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@xxxxxxxxxx>
Acked-by: Minchan Kim <minchan@xxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>

---
 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
@@ -188,8 +188,10 @@ static ssize_t mem_used_total_show(struc
 	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);
 }


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