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Subject[12/85] zram: protect sysfs handler from invalid memory access
3.2.49-rc1 review patch.  If anyone has any objections, please let me know.

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

From: Jiang Liu <liuj97@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@huawei.com>
Acked-by: Minchan Kim <minchan@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
[bwh: Backported to 3.2: adjust context]
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>
---
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
@@ -186,10 +186,12 @@ 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 = xv_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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