linux-kernel - [PATCH] scsi: ppa: Fix use-after-free caused by unfinished delayed work

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Message-Id: <20251201104655.13286-1-duoming@zju.edu.cn>
Date: Mon,  1 Dec 2025 18:46:55 +0800
From: Duoming Zhou <duoming@....edu.cn>
To: linux-scsi@...r.kernel.org
Cc: linux-kernel@...r.kernel.org,
	martin.petersen@...cle.com,
	James.Bottomley@...senPartnership.com,
	Duoming Zhou <duoming@....edu.cn>,
	stable@...nel.org
Subject: [PATCH] scsi: ppa: Fix use-after-free caused by unfinished delayed work

The delayed work item 'ppa_tq' is initialized in __ppa_attach() and
scheduled via ppa_queuecommand() for processing SCSI commands. When
the parallel port SCSI host adapter is detached through ppa_detach(),
the ppa_struct device instance is deallocated.

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

The race condition can occur as follows:

CPU 0(detach thread)   | CPU 1(delayed work)
                       | ppa_queuecommand()
                       |   ppa_queuecommand_lck()
ppa_detach()           |     schedule_delayed_work()
  kfree(dev) //FREE    | ppa_interrupt()
                       |   dev = container_of(...) //USE
                           dev-> //USE

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

This bug was identified through static analysis.

Fixes: 1da177e4c3f4 ("Linux-2.6.12-rc2")
Cc: stable@...nel.org
Signed-off-by: Duoming Zhou <duoming@....edu.cn>
---
 drivers/scsi/ppa.c | 1 +
 1 file changed, 1 insertion(+)

diff --git a/drivers/scsi/ppa.c b/drivers/scsi/ppa.c
index ea682f3044b..8da2a78ebac 100644
--- a/drivers/scsi/ppa.c
+++ b/drivers/scsi/ppa.c
@@ -1136,6 +1136,7 @@ static void ppa_detach(struct parport *pb)
 	ppa_struct *dev;
 	list_for_each_entry(dev, &ppa_hosts, list) {
 		if (dev->dev->port == pb) {
+			disable_delayed_work_sync(&dev->ppa_tq);
 			list_del_init(&dev->list);
 			scsi_remove_host(dev->host);
 			scsi_host_put(dev->host);
-- 
2.34.1