[145/251] zram: avoid invalid memory access in zram_exit()

[Steven Rostedt]

3.6.11.9-rc1 stable review patch.
If anyone has any objections, please let me know.

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

From: Jiang Liu <liuj97@xxxxxxxxx>

[ Upstream commit 6030ea9b35971a4200062f010341ab832e878ac9 ]

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@xxxxxxxxxx>
Cc: stable@xxxxxxxxxxxxxxx
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
Signed-off-by: Steven Rostedt <rostedt@xxxxxxxxxxx>
---
 drivers/staging/zram/zram_drv.c |    2 ++
 1 file changed, 2 insertions(+)

diff --git a/drivers/staging/zram/zram_drv.c b/drivers/staging/zram/zram_drv.c
index 6edefde..38a1b44 100644
--- a/drivers/staging/zram/zram_drv.c
+++ b/drivers/staging/zram/zram_drv.c
@@ -771,9 +771,11 @@ static void __exit zram_exit(void)
 	for (i = 0; i < 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");
-- 
1.7.10.4


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