[PATCH 6.18 156/396] mshv: Fix race in mshv_irqfd_deassign

6.18-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Stanislav Kinsburskii <[email protected]>

[ Upstream commit 0762262ac3e70f65b3bb843fe892f8bac1562d08 ]

mshv_irqfd_deactivate() and the hlist traversal of pt_irqfds_list
require pt->pt_irqfds_lock to be held, but mshv_irqfd_deassign()
omits it. This races with the EPOLLHUP path in mshv_irqfd_wakeup(),
which does take the lock before calling mshv_irqfd_deactivate().

Additionally, mshv_irqfd_deactivate() uses hlist_del() which poisons
the node pointers rather than resetting them. Since
mshv_irqfd_is_active() relies on hlist_unhashed() (checks pprev ==
NULL), a poisoned node still appears active. If a concurrent path calls
mshv_irqfd_deactivate() again on the same irqfd, the guard fails to
prevent a double hlist_del() on poisoned pointers.

Fix both issues:
- Add the missing spin_lock_irq/spin_unlock_irq around the list
  traversal in mshv_irqfd_deassign(), matching mshv_irqfd_release().
- Use hlist_del_init() instead of hlist_del() so the node is properly
  marked as unhashed after removal, making the is_active guard reliable.

Fixes: 621191d709b14 ("Drivers: hv: Introduce mshv_root module to expose /dev/mshv to VMMs")
Signed-off-by: Stanislav Kinsburskii <[email protected]>
Reviewed-by: Anirudh Rayabharam (Microsoft) <[email protected]>
Signed-off-by: Wei Liu <[email protected]>
Signed-off-by: Sasha Levin <[email protected]>
---
 drivers/hv/mshv_eventfd.c | 5 +++--
 1 file changed, 3 insertions(+), 2 deletions(-)

diff --git a/drivers/hv/mshv_eventfd.c b/drivers/hv/mshv_eventfd.c
index 40b7179fee805..586a9f99b3405 100644
--- a/drivers/hv/mshv_eventfd.c
+++ b/drivers/hv/mshv_eventfd.c
@@ -280,7 +280,7 @@ static void mshv_irqfd_deactivate(struct mshv_irqfd *irqfd)
 	if (!mshv_irqfd_is_active(irqfd))
 		return;
 
-	hlist_del(&irqfd->irqfd_hnode);
+	hlist_del_init(&irqfd->irqfd_hnode);
 
 	queue_work(irqfd_cleanup_wq, &irqfd->irqfd_shutdown);
 }
@@ -535,13 +535,14 @@ static int mshv_irqfd_deassign(struct mshv_partition *pt,
 	if (IS_ERR(eventfd))
 		return PTR_ERR(eventfd);
 
+	spin_lock_irq(&pt->pt_irqfds_lock);
 	hlist_for_each_entry_safe(irqfd, n, &pt->pt_irqfds_list,
 				  irqfd_hnode) {
 		if (irqfd->irqfd_eventfd_ctx == eventfd &&
 		    irqfd->irqfd_irqnum == args->gsi)
-
 			mshv_irqfd_deactivate(irqfd);
 	}
+	spin_unlock_irq(&pt->pt_irqfds_lock);
 
 	eventfd_ctx_put(eventfd);
 
-- 
2.53.0