[PATCH ipsec v2] xfrm: fix races in device state cleanup

The deferred-device pass in xfrm_dev_state_flush() finds states under
xfrm_state_dev_gc_lock, but drops the lock before calling
xfrm_dev_state_free() because the driver callback may sleep. The device
GC list does not hold an xfrm_state reference, so the state GC worker can
destroy the same state concurrently.

The race can proceed as follows:

  CPU 0                               CPU 1
  find x on the device GC list
  drop xfrm_state_dev_gc_lock
                                      xfrm_state_gc_destroy(x)
                                        xfrm_dev_state_free(x)
                                        xfrm_state_free(x)
  xfrm_dev_state_free(x)

Both paths can invoke the driver callback and drop the device reference.
CPU 0 can also access the xfrm_state after CPU 1 has freed it.

KASAN reported:

  BUG: KASAN: slab-use-after-free in xfrm_dev_state_free+0x24c/0x2a0
  Read of size 8 at addr ffff88810bbaa960 by task poc/102

  Call Trace:
   xfrm_dev_state_free+0x24c/0x2a0
   xfrm_dev_state_flush+0x353/0x400
   xfrm_dev_event+0x26d/0x3a0
   notifier_call_chain+0xc0/0x280
   __dev_notify_flags+0x169/0x250
   netif_change_flags+0xe7/0x160
   dev_change_flags+0x96/0x220
   devinet_ioctl+0x7f4/0x1880

  Freed by task 57:
   kmem_cache_free+0xcb/0x3d0
   xfrm_state_gc_task+0x4a8/0x650
   process_one_work+0x63a/0x1070

A third xfrm_dev_state_free() caller in xfrm_state_find() can also race
with the deferred pass. Both callers can sample the same device before
either clears xso->dev, then invoke the callback and netdev_put() twice.
Since hlist_del() leaves the node poisoned rather than unhashed, they can
also unlink the device GC node twice.

Acquire a state reference while the deferred pass still holds
xfrm_state_dev_gc_lock. If the reference count is already zero, leave
destruction to the state GC worker. Also claim device cleanup under the
same lock by clearing xso->dev and unlinking the node with
hlist_del_init(). Only the caller that claims the device invokes the
callback and drops the device reference. The deferred pass releases its
temporary state reference after cleanup.

Fixes: 07b87f9eea0c ("xfrm: Fix unregister netdevice hang on hardware offload.")
Cc: stable@vger.kernel.org
Signed-off-by: Chengfeng Ye <redacted>
---

Changes in v2:
- Replace the global mutex with a temporary state reference acquired
  while walking the device GC list.
- Claim device cleanup under xfrm_state_dev_gc_lock so concurrent
  callers cannot run the callback or netdev_put() twice.
- Use hlist_del_init() to leave the device GC node unhashed.
- Cover the xfrm_state_find() cleanup path identified during review.

v1: https://lore.kernel.org/netdev/20260730103543.2077749-1-nicoyip.dev@gmail.com/ (local)

 net/xfrm/xfrm_state.c | 16 ++++++++++------
 1 file changed, 10 insertions(+), 6 deletions(-)

diff --git a/net/xfrm/xfrm_state.c b/net/xfrm/xfrm_state.c
index 36a4f6793ede..282d09d0c247 100644
--- a/net/xfrm/xfrm_state.c
+++ b/net/xfrm/xfrm_state.c

@@ -780,17 +780,20 @@ EXPORT_SYMBOL_GPL(xfrm_dev_state_delete);
 void xfrm_dev_state_free(struct xfrm_state *x)
 {
 	struct xfrm_dev_offload *xso = &x->xso;
-	struct net_device *dev = READ_ONCE(xso->dev);
+	struct net_device *dev;
 
+	spin_lock_bh(&xfrm_state_dev_gc_lock);
+	dev = READ_ONCE(xso->dev);
 	if (dev && dev->xfrmdev_ops) {
-		spin_lock_bh(&xfrm_state_dev_gc_lock);
+		WRITE_ONCE(xso->dev, NULL);
 		if (!hlist_unhashed(&x->dev_gclist))
-			hlist_del(&x->dev_gclist);
-		spin_unlock_bh(&xfrm_state_dev_gc_lock);
+			hlist_del_init(&x->dev_gclist);
+	}
+	spin_unlock_bh(&xfrm_state_dev_gc_lock);
 
+	if (dev && dev->xfrmdev_ops) {
 		if (dev->xfrmdev_ops->xdo_dev_state_free)
 			dev->xfrmdev_ops->xdo_dev_state_free(dev, x);
-		WRITE_ONCE(xso->dev, NULL);
 		xso->type = XFRM_DEV_OFFLOAD_UNSPECIFIED;
 		netdev_put(dev, &xso->dev_tracker);
 	}

@@ -1005,9 +1008,10 @@ int xfrm_dev_state_flush(struct net *net, struct net_device *dev, bool task_vali
 	hlist_for_each_entry_safe(x, tmp, &xfrm_state_dev_gc_list, dev_gclist) {
 		xso = &x->xso;
 
-		if (xso->dev == dev) {
+		if (xso->dev == dev && xfrm_state_hold_rcu(x)) {
 			spin_unlock_bh(&xfrm_state_dev_gc_lock);
 			xfrm_dev_state_free(x);
+			xfrm_state_put(x);
 			spin_lock_bh(&xfrm_state_dev_gc_lock);
 			goto restart_gc;
 		}

base-commit: e6b6078ea1731b05b3b552497b3bce4bf8b014ae
-- 
2.43.0