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Subject[08/85] zram: avoid invalid memory access in zram_exit()
3.2.49-rc1 review patch.  If anyone has any objections, please let me know.

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

From: Jiang Liu <liuj97@gmail.com>

commit 6030ea9b35971a4200062f010341ab832e878ac9 upstream.

Memory for zram->disk object may have already been freed after returning
from destroy_device(zram), then it's unsafe for zram_reset_device(zram)
to access zram->disk again.

We can't solve this bug by flipping the order of destroy_device(zram)
and zram_reset_device(zram), that will cause deadlock issues to the
zram sysfs handler.

So fix it by holding an extra reference to zram->disk before calling
destroy_device(zram).

Signed-off-by: Jiang Liu <jiang.liu@huawei.com>
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_drv.c | 2 ++
1 file changed, 2 insertions(+)

--- a/drivers/staging/zram/zram_drv.c
+++ b/drivers/staging/zram/zram_drv.c
@@ -846,9 +846,11 @@ static void __exit zram_exit(void)
for (i = 0; i < zram_num_devices; i++) {
zram = &zram_devices[i];

+ get_disk(zram->disk);
destroy_device(zram);
if (zram->init_done)
zram_reset_device(zram);
+ put_disk(zram->disk);
}

unregister_blkdev(zram_major, "zram");


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