[PATCH] scsi: imm: fix use-after-free bugs caused by unfinished delayed work

[Duoming Zhou]

The delayed work item imm_tq is initialized in imm_attach() and
scheduled via imm_queuecommand() for processing SCSI commands.
When the IMM parallel port SCSI host adapter is detached through
imm_detach(), the imm_struct device instance is deallocated.

However, the delayed work might still be pending or executing
when imm_detach() is called, leading to use-after-free bugs
when the work function imm_interrupt() accesses the already
freed imm_struct memory.

The race condition can occur as follows:

CPU 0(detach thread)   | CPU 1
                       | imm_queuecommand()
                       |   imm_queuecommand_lck()
imm_detach()           |     schedule_delayed_work()
  kfree(dev) //FREE    | imm_interrupt()
                       |   dev = container_of(...) //USE
                           dev-> //USE

Add disable_delayed_work_sync() in imm_detach() to guarantee
proper cancellation of the delayed work item before imm_struct
is deallocated.

Fixes: 1da177e4c3f4 ("Linux-2.6.12-rc2")
Signed-off-by: Duoming Zhou <duoming@xxxxxxxxxx>
---
 drivers/scsi/imm.c | 1 +
 1 file changed, 1 insertion(+)

diff --git a/drivers/scsi/imm.c b/drivers/scsi/imm.c
index 5c602c057798..45b0e33293a5 100644
--- a/drivers/scsi/imm.c
+++ b/drivers/scsi/imm.c
@@ -1260,6 +1260,7 @@ static void imm_detach(struct parport *pb)
 	imm_struct *dev;
 	list_for_each_entry(dev, &imm_hosts, list) {
 		if (dev->dev->port == pb) {
+			disable_delayed_work_sync(&dev->imm_tq);
 			list_del_init(&dev->list);
 			scsi_remove_host(dev->host);
 			scsi_host_put(dev->host);
-- 
2.34.1