linux-kernel - Re: [PATCH] virtio_ring: Fix mem leak with vring_new

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Date:   Tue, 25 Feb 2020 13:39:41 +0800
From:   Jason Wang <jasowang@...hat.com>
To:     Suman Anna <s-anna@...com>, "Michael S. Tsirkin" <mst@...hat.com>
Cc:     Tiwei Bie <tiwei.bie@...el.com>,
        "David S. Miller" <davem@...emloft.net>,
        virtualization@...ts.linux-foundation.org,
        linux-kernel@...r.kernel.org, linux-remoteproc@...r.kernel.org
Subject: Re: [PATCH] virtio_ring: Fix mem leak with vring_new_virtqueue()


On 2020/2/25 上午5:26, Suman Anna wrote:
> The functions vring_new_virtqueue() and __vring_new_virtqueue() are used
> with split rings, and any allocations within these functions are managed
> outside of the .we_own_ring flag. The commit cbeedb72b97a ("virtio_ring:
> allocate desc state for split ring separately") allocates the desc state
> within the __vring_new_virtqueue() but frees it only when the .we_own_ring
> flag is set. This leads to a memory leak when freeing such allocated
> virtqueues with the vring_del_virtqueue() function.
>
> Fix this by moving the desc_state free code outside the flag and only
> for split rings. Issue was discovered during testing with remoteproc
> and virtio_rpmsg.
>
> Fixes: cbeedb72b97a ("virtio_ring: allocate desc state for split ring separately")
> Signed-off-by: Suman Anna <s-anna@...com>
> ---
>   drivers/virtio/virtio_ring.c | 4 ++--
>   1 file changed, 2 insertions(+), 2 deletions(-)
>
> diff --git a/drivers/virtio/virtio_ring.c b/drivers/virtio/virtio_ring.c
> index 867c7ebd3f10..58b96baa8d48 100644
> --- a/drivers/virtio/virtio_ring.c
> +++ b/drivers/virtio/virtio_ring.c
> @@ -2203,10 +2203,10 @@ void vring_del_virtqueue(struct virtqueue *_vq)
>   					 vq->split.queue_size_in_bytes,
>   					 vq->split.vring.desc,
>   					 vq->split.queue_dma_addr);
> -
> -			kfree(vq->split.desc_state);
>   		}
>   	}
> +	if (!vq->packed_ring)
> +		kfree(vq->split.desc_state);


Nitpick, it looks to me it would be more clear if we just free 
desc_state unconditionally here (and remove the kfree for packed above).

Anyway desc_state will be allocated by use even if !we_own_ring.

Thanks


>   	list_del(&_vq->list);
>   	kfree(vq);
>   }