virtio_net: fix missing lock protection on control_buf access

Refactored the handling of control_buf to be within the cvq_lock
critical section, mitigating race conditions between reading device
responses and new command submissions.

Fixes: 6f45ab3e ("virtio_net: Add a lock for the command VQ.")
Signed-off-by: Heng Qi <hengqi@linux.alibaba.com>
Reviewed-by: Hariprasad Kelam <hkelam@marvell.com>
Acked-by: Jason Wang <jasowang@redhat.com>
Reviewed-by: Xuan Zhuo <xuanzhuo@linux.alibaba.com>
Link: https://lore.kernel.org/r/20240530034143.19579-1-hengqi@linux.alibaba.comSigned-off-by: Jakub Kicinski <kuba@kernel.org>

drivers/net/virtio_net.c

@@ -2686,6 +2686,7 @@ static bool virtnet_send_command_reply(struct virtnet_info *vi, u8 class, u8 cmd
 {
 	struct scatterlist *sgs[5], hdr, stat;
 	u32 out_num = 0, tmp, in_num = 0;
+	bool ok;
 	int ret;
 
 	/* Caller should know better */
@@ -2731,8 +2732,9 @@ static bool virtnet_send_command_reply(struct virtnet_info *vi, u8 class, u8 cmd
 	}
 
 unlock:
+	ok = vi->ctrl->status == VIRTIO_NET_OK;
 	mutex_unlock(&vi->cvq_lock);
-	return vi->ctrl->status == VIRTIO_NET_OK;
+	return ok;
 }
 
 static bool virtnet_send_command(struct virtnet_info *vi, u8 class, u8 cmd,