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

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Message-ID: <0ace3a3b-cf2f-7977-5337-f74f530afbe1@ti.com>
Date:   Tue, 25 Feb 2020 10:51:52 -0600
From:   Suman Anna <s-anna@...com>
To:     Jason Wang <jasowang@...hat.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()

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

> Anyway desc_state will be allocated by use even if !we_own_ring.
> 
> Thanks
> 
> 
>>       list_del(&_vq->list);
>>       kfree(vq);
>>   }
>