[PATCH] vsock/virtio: prevent workers from using deleted virtqueues

[Weiming Shi]

The RX, TX and event workers read their virtqueue pointers before taking
the mutex that protects the queue and its run flag. A work item delayed
across freeze and restore can therefore retain a pointer deleted by
virtio_vsock_vqs_del(), observe the run flag for the replacement queues,
and use the freed pointer.

RX has an additional path: when rx_run is clear, the common exit still
refills the RX queue. A queued worker can consequently call
virtqueue_add_sgs() immediately after freeze deletes the virtqueues.

BUG: KASAN: slab-use-after-free in virtqueue_add_sgs
Read of size 4 by task kworker/2:1
Workqueue: virtio_vsock virtio_transport_rx_work
Call Trace:
 virtqueue_add_sgs (drivers/virtio/virtio_ring.c:2796)
 virtio_vsock_rx_fill (net/vmw_vsock/virtio_transport.c:332)
 virtio_transport_rx_work (net/vmw_vsock/virtio_transport.c:701)
 process_one_work (kernel/workqueue.c:3314)
 worker_thread (kernel/workqueue.c:3478)
 kthread (kernel/kthread.c:436)
 ret_from_fork (arch/x86/kernel/process.c:158)
 ret_from_fork_asm (arch/x86/entry/entry_64.S:245)
...
Freed by task 141:
 kfree (mm/slub.c:6566)
 vp_del_vq (drivers/virtio/virtio_pci_common.c:259)
 vp_del_vqs (drivers/virtio/virtio_pci_common.c:285)
 virtio_vsock_freeze (net/vmw_vsock/virtio_transport.c:912)
 virtio_device_freeze (drivers/virtio/virtio.c:658)
 virtio_pci_freeze (drivers/virtio/virtio_pci_common.c:601)
 pci_pm_freeze (drivers/pci/pci-driver.c:1098)
 device_suspend (drivers/base/power/main.c:1968)
Kernel panic - not syncing: KASAN: panic_on_warn set ...

Read each worker's virtqueue under its mutex after confirming that the
queue is running, and only refill RX while RX is running.

Fixes: b917507e5ad9 ("vsock/virtio: stop workers during the .remove()")
Cc: stable@xxxxxxxxxxxxxxx
Reported-by: Xiang Mei <xmei5@xxxxxxx>
Assisted-by: OpenAI-Codex:gpt-5
Signed-off-by: Weiming Shi <bestswngs@xxxxxxxxx>
---
 net/vmw_vsock/virtio_transport.c | 14 ++++++++------
 1 file changed, 8 insertions(+), 6 deletions(-)

diff --git a/net/vmw_vsock/virtio_transport.c b/net/vmw_vsock/virtio_transport.c
index 57f2d6ec3ffc..79cf19f58943 100644
--- a/net/vmw_vsock/virtio_transport.c
+++ b/net/vmw_vsock/virtio_transport.c
@@ -346,12 +346,13 @@ static void virtio_transport_tx_work(struct work_struct *work)
 	struct virtqueue *vq;
 	bool added = false;
 
-	vq = vsock->vqs[VSOCK_VQ_TX];
 	mutex_lock(&vsock->tx_lock);
 
 	if (!vsock->tx_run)
 		goto out;
 
+	vq = vsock->vqs[VSOCK_VQ_TX];
+
 	do {
 		struct sk_buff *skb;
 		unsigned int len;
@@ -451,13 +452,13 @@ static void virtio_transport_event_work(struct work_struct *work)
 		container_of(work, struct virtio_vsock, event_work);
 	struct virtqueue *vq;
 
-	vq = vsock->vqs[VSOCK_VQ_EVENT];
-
 	mutex_lock(&vsock->event_lock);
 
 	if (!vsock->event_run)
 		goto out;
 
+	vq = vsock->vqs[VSOCK_VQ_EVENT];
+
 	do {
 		struct virtio_vsock_event *event;
 		unsigned int len;
@@ -634,13 +635,13 @@ static void virtio_transport_rx_work(struct work_struct *work)
 		container_of(work, struct virtio_vsock, rx_work);
 	struct virtqueue *vq;
 
-	vq = vsock->vqs[VSOCK_VQ_RX];
-
 	mutex_lock(&vsock->rx_lock);
 
 	if (!vsock->rx_run)
 		goto out;
 
+	vq = vsock->vqs[VSOCK_VQ_RX];
+
 	do {
 		virtqueue_disable_cb(vq);
 		for (;;) {
@@ -689,7 +690,8 @@ static void virtio_transport_rx_work(struct work_struct *work)
 	} while (!virtqueue_enable_cb(vq));
 
 out:
-	if (vsock->rx_buf_nr < vsock->rx_buf_max_nr / 2)
+	if (vsock->rx_run &&
+	    vsock->rx_buf_nr < vsock->rx_buf_max_nr / 2)
 		virtio_vsock_rx_fill(vsock);
 	mutex_unlock(&vsock->rx_lock);
 }
-- 
2.55.0