There is one race case in vduse_dev_msg_sync and vduse_dev_read_iter:

vduse_dev_read_iter():
    lock(msg_lock);
    dequeue_msg(send_list);
    unlock(msg_lock);
vduse_dev_msg_sync():
    wait_timeout() finish
    lock(msg_lock);
    check msg->complete is false
        list_del(msg);   <- double list_del() crash!

To fix this case, we shall ensure vduse_msg is on send_list or recv_list
outside the msg_lock critical section.

Fixes: c8a6153b6c59 ("vduse: Introduce VDUSE - vDPA Device in Userspace")
Cc: stable@vger.kernel.org
Signed-off-by: Zhang Tianci <zhangtianci.1997@bytedance.com>
Reviewed-by: Xie Yongji <xieyongji@bytedance.com>
---
 drivers/vdpa/vdpa_user/vduse_dev.c | 30 ++++++++++++++++++++++--------
 1 file changed, 22 insertions(+), 8 deletions(-)

diff --git a/drivers/vdpa/vdpa_user/vduse_dev.c b/drivers/vdpa/vdpa_user/vduse_dev.c
index b37f18a0ce6fd..1e274688bba32 100644
--- a/drivers/vdpa/vdpa_user/vduse_dev.c
+++ b/drivers/vdpa/vdpa_user/vduse_dev.c
@@ -331,6 +331,7 @@ static ssize_t vduse_dev_read_iter(struct kiocb *iocb, struct iov_iter *to)
 	struct file *file = iocb->ki_filp;
 	struct vduse_dev *dev = file->private_data;
 	struct vduse_dev_msg *msg;
+	struct vduse_dev_request req;
 	int size = sizeof(struct vduse_dev_request);
 	ssize_t ret;
 
@@ -345,7 +346,7 @@ static ssize_t vduse_dev_read_iter(struct kiocb *iocb, struct iov_iter *to)
 
 		ret = -EAGAIN;
 		if (file->f_flags & O_NONBLOCK)
-			goto unlock;
+			break;
 
 		spin_unlock(&dev->msg_lock);
 		ret = wait_event_interruptible_exclusive(dev->waitq,
@@ -355,17 +356,30 @@ static ssize_t vduse_dev_read_iter(struct kiocb *iocb, struct iov_iter *to)
 
 		spin_lock(&dev->msg_lock);
 	}
+	if (!msg) {
+		spin_unlock(&dev->msg_lock);
+		return ret;
+	}
+
+	memcpy(&req, &msg->req, sizeof(req));
+	/*
+	 * We must ensure vduse_msg is on send_list or recv_list before unlock
+	 * dev->msg_lock. Because vduse_dev_msg_sync() may be timeout when we
+	 * copy data to userspace, and will call list_del() for this msg.
+	 */
+	vduse_enqueue_msg(&dev->recv_list, msg);
 	spin_unlock(&dev->msg_lock);
-	ret = copy_to_iter(&msg->req, size, to);
-	spin_lock(&dev->msg_lock);
+
+	ret = copy_to_iter(&req, size, to);
 	if (ret != size) {
+		spin_lock(&dev->msg_lock);
+		/* Roll back: move msg back to send_list if still pending. */
+		msg = vduse_find_msg(&dev->recv_list, req.request_id);
+		if (msg)
+			vduse_enqueue_msg_head(&dev->send_list, msg);
+		spin_unlock(&dev->msg_lock);
 		ret = -EFAULT;
-		vduse_enqueue_msg_head(&dev->send_list, msg);
-		goto unlock;
 	}
-	vduse_enqueue_msg(&dev->recv_list, msg);
-unlock:
-	spin_unlock(&dev->msg_lock);
 
 	return ret;
 }
-- 
2.39.5