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

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Date:   Sun, 8 Mar 2020 03:58:05 -0400
From:   "Michael S. Tsirkin" <mst@...hat.com>
To:     Suman Anna <s-anna@...com>
Cc:     Jason Wang <jasowang@...hat.com>, 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 Thu, Mar 05, 2020 at 06:27:53PM -0600, Suman Anna wrote:
> On 2/25/20 9:13 PM, Jason Wang wrote:
> > 
> > On 2020/2/26 上午12:51, Suman Anna wrote:
> >> Hi Jason,
> >>
> >> On 2/24/20 11:39 PM, Jason Wang wrote:
> >>> 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).
> >> OK, are you sure you want that to be folded into this patch? It looks to
> >> me a separate cleanup/consolidation patch, and packed desc_state does
> >> not suffer this memleak, and need not be backported into stable kernels.
> >>
> >> regards
> >> Suman
> > 
> > 
> > Though it's just a small tweak, I'm fine for leaving it for future.
> > 
> > So
> > 
> > Acked-by: Jason Wang <jasowang@...hat.com>
> > 
> 
> Mike,
> Ping on this. I don't see the patch in -next yet. Can we get this into
> the current -rc please?
> 
> regards
> Suman

Yes will queue it shortly, thanks!