From 7b6f2e3c29fb4d76f1e4973280792eabbd526602 Mon Sep 17 00:00:00 2001 From: Yizhou Zhao Date: Tue, 9 Jun 2026 23:52:01 +0800 Subject: [PATCH] 9p/xen: drain response work after unbinding IRQ commit ea4f1009408e ("9p/xen : Fix use after free bug in xen_9pfs_front_remove due to race condition") added cancel_work_sync() to keep xen_9pfs_front_free() from freeing a ring while p9_xen_response() is still running. The work is currently drained before the event channel IRQ is unbound. That leaves a race window where xen_9pfs_front_event_handler() can run after cancel_work_sync() returns and queue p9_xen_response() again. The following unbind_from_irqhandler() synchronizes with the IRQ handler, but it does not cancel work that the handler already queued. The teardown can then free the ring and private data while the response work remains pending, and the worker later dereferences ring->priv and priv->client. Unbind the event channel IRQ before draining the work. Once the IRQ is unbound, no new response work can be queued by the backend event channel, and cancel_work_sync() waits for any work that was queued before or during the unbind. It is then safe to release the ring resources. Fixes: ea4f1009408e ("9p/xen : Fix use after free bug in xen_9pfs_front_remove due to race condition") Cc: stable@vger.kernel.org Reported-by: Yizhou Zhao Reported-by: Yuxiang Yang Reported-by: Ao Wang Reported-by: Xuewei Feng Reported-by: Qi Li Reported-by: Ke Xu Assisted-by: GLM:GLM-5.1 Signed-off-by: Yizhou Zhao Message-ID: <20260609155202.1706-1-zhaoyz24@mails.tsinghua.edu.cn> Signed-off-by: Dominique Martinet --- net/9p/trans_xen.c | 4 ++-- 1 file changed, 2 insertions(+), 2 deletions(-) diff --git a/net/9p/trans_xen.c b/net/9p/trans_xen.c index 5a0b5b83e8ab..9ee1ac9143d4 100644 --- a/net/9p/trans_xen.c +++ b/net/9p/trans_xen.c @@ -282,14 +282,14 @@ static void xen_9pfs_front_free(struct xen_9pfs_front_priv *priv) for (i = 0; i < XEN_9PFS_NUM_RINGS; i++) { struct xen_9pfs_dataring *ring = &priv->rings[i]; - cancel_work_sync(&ring->work); - if (!ring->intf) break; if (ring->irq >= 0) { unbind_from_irqhandler(ring->irq, ring); ring->irq = -1; } + cancel_work_sync(&ring->work); + if (ring->data.in) { for (j = 0; j < (1 << ring->intf->ring_order); j++) { grant_ref_t ref;