linux-kernel - Re: [PATCH] vhost_net: Convert from atomic_t to refcount_t on vhost_net_ubuf

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Date:   Sun, 5 Sep 2021 12:17:55 -0400
From:   "Michael S. Tsirkin" <mst@...hat.com>
To:     Xiyu Yang <xiyuyang19@...an.edu.cn>
Cc:     Jason Wang <jasowang@...hat.com>, kvm@...r.kernel.org,
        virtualization@...ts.linux-foundation.org, netdev@...r.kernel.org,
        linux-kernel@...r.kernel.org, yuanxzhang@...an.edu.cn,
        Xin Tan <tanxin.ctf@...il.com>
Subject: Re: [PATCH] vhost_net: Convert from atomic_t to refcount_t on
 vhost_net_ubuf_ref->refcount

On Sat, Jul 17, 2021 at 06:20:30PM +0800, Xiyu Yang wrote:
> refcount_t type and corresponding API can protect refcounters from
> accidental underflow and overflow and further use-after-free situations.
> 
> Signed-off-by: Xiyu Yang <xiyuyang19@...an.edu.cn>
> Signed-off-by: Xin Tan <tanxin.ctf@...il.com>

Pls resubmit after addressing the build bot comments.
Thanks!

> ---
>  drivers/vhost/net.c | 14 ++++++++------
>  1 file changed, 8 insertions(+), 6 deletions(-)
> 
> diff --git a/drivers/vhost/net.c b/drivers/vhost/net.c
> index 6414bd5741b8..e23150ca7d4c 100644
> --- a/drivers/vhost/net.c
> +++ b/drivers/vhost/net.c
> @@ -5,6 +5,7 @@
>   * virtio-net server in host kernel.
>   */
>  
> +#include <linux/refcount.h>
>  #include <linux/compat.h>
>  #include <linux/eventfd.h>
>  #include <linux/vhost.h>
> @@ -92,7 +93,7 @@ struct vhost_net_ubuf_ref {
>  	 *  1: no outstanding ubufs
>  	 * >1: outstanding ubufs
>  	 */
> -	atomic_t refcount;
> +	refcount_t refcount;
>  	wait_queue_head_t wait;
>  	struct vhost_virtqueue *vq;
>  };
> @@ -240,7 +241,7 @@ vhost_net_ubuf_alloc(struct vhost_virtqueue *vq, bool zcopy)
>  	ubufs = kmalloc(sizeof(*ubufs), GFP_KERNEL);
>  	if (!ubufs)
>  		return ERR_PTR(-ENOMEM);
> -	atomic_set(&ubufs->refcount, 1);
> +	refcount_set(&ubufs->refcount, 1);
>  	init_waitqueue_head(&ubufs->wait);
>  	ubufs->vq = vq;
>  	return ubufs;
> @@ -248,7 +249,8 @@ vhost_net_ubuf_alloc(struct vhost_virtqueue *vq, bool zcopy)
>  
>  static int vhost_net_ubuf_put(struct vhost_net_ubuf_ref *ubufs)
>  {
> -	int r = atomic_sub_return(1, &ubufs->refcount);
> +	refcount_dec(&ubufs->refcount);
> +	int r = refcount_read(&ubufs->refcount);
>  	if (unlikely(!r))
>  		wake_up(&ubufs->wait);
>  	return r;
> @@ -257,7 +259,7 @@ static int vhost_net_ubuf_put(struct vhost_net_ubuf_ref *ubufs)
>  static void vhost_net_ubuf_put_and_wait(struct vhost_net_ubuf_ref *ubufs)
>  {
>  	vhost_net_ubuf_put(ubufs);
> -	wait_event(ubufs->wait, !atomic_read(&ubufs->refcount));
> +	wait_event(ubufs->wait, !refcount_read(&ubufs->refcount));
>  }
>  
>  static void vhost_net_ubuf_put_wait_and_free(struct vhost_net_ubuf_ref *ubufs)
> @@ -909,7 +911,7 @@ static void handle_tx_zerocopy(struct vhost_net *net, struct socket *sock)
>  			ctl.ptr = ubuf;
>  			msg.msg_controllen = sizeof(ctl);
>  			ubufs = nvq->ubufs;
> -			atomic_inc(&ubufs->refcount);
> +			refcount_inc(&ubufs->refcount);
>  			nvq->upend_idx = (nvq->upend_idx + 1) % UIO_MAXIOV;
>  		} else {
>  			msg.msg_control = NULL;
> @@ -1384,7 +1386,7 @@ static void vhost_net_flush(struct vhost_net *n)
>  		vhost_net_ubuf_put_and_wait(n->vqs[VHOST_NET_VQ_TX].ubufs);
>  		mutex_lock(&n->vqs[VHOST_NET_VQ_TX].vq.mutex);
>  		n->tx_flush = false;
> -		atomic_set(&n->vqs[VHOST_NET_VQ_TX].ubufs->refcount, 1);
> +		refcount_set(&n->vqs[VHOST_NET_VQ_TX].ubufs->refcount, 1);
>  		mutex_unlock(&n->vqs[VHOST_NET_VQ_TX].vq.mutex);
>  	}
>  }
> -- 
> 2.7.4