[PATCH] amt: fix use-after-free in AMT delayed works

[Shihuang Liu <shlomojune6@gmail.com>]

When an AMT device is removed, pending delayed works can still access
the freed amt_dev structure, which may result in kernel crashes or
memory corruption.

amt_dev_stop() cancels req_wq and discovery_wq with
cancel_delayed_work_sync(), but these works can be scheduled again
from event_wq after the cancellation. This allows delayed works to
access the freed amt_dev structure after the netdev has been released.

The following is a simple race scenario:

CPU0                         CPU1

amt_dev_stop()
cancel_delayed_work_sync()
                             amt_event_work()
                             mod_delayed_work(req_wq)
free netdev
                             req_wq accesses freed amt_dev

Use disable_delayed_work_sync() in amt_dev_stop() to prevent req_wq and
discovery_wq from being queued again and wait for running work items
to complete.

The delayed works are disabled after initialization in
amt_newlink() and enabled only when the device is successfully opened.
This keeps the delayed work lifecycle synchronized with the lifetime
of the AMT device.

Fixes: cbc21dc1cfe9 ("amt: add data plane of amt interface")
Cc: stable@vger.kernel.org
Signed-off-by: Shihuang Liu <shlomojune6@gmail.com>
---
 drivers/net/amt.c | 14 +++++++++++---
 1 file changed, 11 insertions(+), 3 deletions(-)

diff --git a/drivers/net/amt.c b/drivers/net/amt.c
index 951dd10e192b..7eb871b9b7e1 100644
--- a/drivers/net/amt.c
+++ b/drivers/net/amt.c
@@ -2995,9 +2995,15 @@ static int amt_dev_open(struct net_device *dev)
 	amt->event_idx = 0;
 	amt->nr_events = 0;
 
+	enable_delayed_work(&amt->discovery_wq);
+	enable_delayed_work(&amt->req_wq);
+
 	err = amt_socket_create(amt);
-	if (err)
+	if (err) {
+		disable_delayed_work(&amt->req_wq);
+		disable_delayed_work(&amt->discovery_wq);
 		return err;
+	}
 
 	amt->req_cnt = 0;
 	amt->remote_ip = 0;
@@ -3023,8 +3029,8 @@ static int amt_dev_stop(struct net_device *dev)
 	struct sock *sk;
 	int i;
 
-	cancel_delayed_work_sync(&amt->req_wq);
-	cancel_delayed_work_sync(&amt->discovery_wq);
+	disable_delayed_work_sync(&amt->req_wq);
+	disable_delayed_work_sync(&amt->discovery_wq);
 	cancel_delayed_work_sync(&amt->secret_wq);
 
 	/* shutdown */
@@ -3278,6 +3284,8 @@ static int amt_newlink(struct net_device *dev,
 	INIT_DELAYED_WORK(&amt->req_wq, amt_req_work);
 	INIT_DELAYED_WORK(&amt->secret_wq, amt_secret_work);
 	INIT_WORK(&amt->event_wq, amt_event_work);
+	disable_delayed_work(&amt->req_wq);
+	disable_delayed_work(&amt->discovery_wq);
 	INIT_LIST_HEAD(&amt->tunnel_list);
 	return 0;
 err:
-- 
2.43.0