[PATCH v3 net] cnic: Fix use-after-free bugs in cnic_delete_task

[PATCH v3 net] cnic: Fix use-after-free bugs in cnic_delete_task

[Duoming Zhou]

The original code uses cancel_delayed_work() in cnic_cm_stop_bnx2x_hw(),
which does not guarantee that the delayed work item 'delete_task' has
fully completed if it was already running. Additionally, the delayed work
item is cyclic, the flush_workqueue() in cnic_cm_stop_bnx2x_hw() only
blocks and waits for work items that were already queued to the
workqueue prior to its invocation. Any work items submitted after
flush_workqueue() is called are not included in the set of tasks that the
flush operation awaits. This means that after the cyclic work items have
finished executing, a delayed work item may still exist in the workqueue.
This leads to use-after-free scenarios where the cnic_dev is deallocated
by cnic_free_dev(), while delete_task remains active and attempt to
dereference cnic_dev in cnic_delete_task().

A typical race condition is illustrated below:

CPU 0 (cleanup)              | CPU 1 (delayed work callback)
cnic_netdev_event()          |
  cnic_stop_hw()             | cnic_delete_task()
    cnic_cm_stop_bnx2x_hw()  | ...
      cancel_delayed_work()  | /* the queue_delayed_work()
      flush_workqueue()      |    executes after flush_workqueue()*/
                             | queue_delayed_work()
  cnic_free_dev(dev)//free   | cnic_delete_task() //new instance
                             |   dev = cp->dev; //use

Replace cancel_delayed_work() with cancel_delayed_work_sync() to ensure
that the cyclic delayed work item is properly canceled and that any
ongoing execution of the work item completes before the cnic_dev is
deallocated. Furthermore, since cancel_delayed_work_sync() uses
__flush_work(work, true) to synchronously wait for any currently
executing instance of the work item to finish, the flush_workqueue()
becomes redundant and should be removed.

This bug was identified through static analysis. To reproduce the issue
and validate the fix, I simulated the cnic PCI device in QEMU and
introduced intentional delays — such as inserting calls to ssleep()
within the cnic_delete_task() function — to increase the likelihood
of triggering the bug.

Fixes: fdf24086f475 ("cnic: Defer iscsi connection cleanup")
Signed-off-by: Duoming Zhou <duoming@zju.edu.cn>
---
Changes in v3:
  - Add how I discovered and tested the patch in the commit message.
  - Remove flush_workqueue() in cnic_cm_stop_bnx2x_hw().

 drivers/net/ethernet/broadcom/cnic.c | 3 +--
 1 file changed, 1 insertion(+), 2 deletions(-)

diff --git a/drivers/net/ethernet/broadcom/cnic.c b/drivers/net/ethernet/broadcom/cnic.c
index a9040c42d2ff..6e97a5a7daaf 100644
--- a/drivers/net/ethernet/broadcom/cnic.c
+++ b/drivers/net/ethernet/broadcom/cnic.c
@@ -4230,8 +4230,7 @@ static void cnic_cm_stop_bnx2x_hw(struct cnic_dev *dev)
 
 	cnic_bnx2x_delete_wait(dev, 0);
 
-	cancel_delayed_work(&cp->delete_task);
-	flush_workqueue(cnic_wq);
+	cancel_delayed_work_sync(&cp->delete_task);
 
 	if (atomic_read(&cp->iscsi_conn) != 0)
 		netdev_warn(dev->netdev, "%d iSCSI connections not destroyed\n",
-- 
2.34.1

Re: [PATCH v3 net] cnic: Fix use-after-free bugs in cnic_delete_task

[patchwork-bot+netdevbpf]

Hello:

This patch was applied to netdev/net.git (main)
by Jakub Kicinski <kuba@kernel.org>:

On Wed, 17 Sep 2025 13:46:02 +0800 you wrote:
> The original code uses cancel_delayed_work() in cnic_cm_stop_bnx2x_hw(),
> which does not guarantee that the delayed work item 'delete_task' has
> fully completed if it was already running. Additionally, the delayed work
> item is cyclic, the flush_workqueue() in cnic_cm_stop_bnx2x_hw() only
> blocks and waits for work items that were already queued to the
> workqueue prior to its invocation. Any work items submitted after
> flush_workqueue() is called are not included in the set of tasks that the
> flush operation awaits. This means that after the cyclic work items have
> finished executing, a delayed work item may still exist in the workqueue.
> This leads to use-after-free scenarios where the cnic_dev is deallocated
> by cnic_free_dev(), while delete_task remains active and attempt to
> dereference cnic_dev in cnic_delete_task().
> 
> [...]

Here is the summary with links:
  - [v3,net] cnic: Fix use-after-free bugs in cnic_delete_task
    https://git.kernel.org/netdev/net/c/cfa7d9b1e3a8

You are awesome, thank you!
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