Re: [PATCH] virtio_ring: Fix mem leak with vring_new_virtqueue()

[Suman Anna]

Hi Jason,

On 2/24/20 11:39 PM, Jason Wang wrote:
> 
> On 2020/2/25 äå5:26, 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@xxxxxx>
>> ---
>> Â drivers/virtio/virtio_ring.c | 4 ++--
>> Â 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)
>> ÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂ vq->split.queue_size_in_bytes,
>> ÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂ vq->split.vring.desc,
>> ÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂ vq->split.queue_dma_addr);
>> -
>> -ÂÂÂÂÂÂÂÂÂÂÂ kfree(vq->split.desc_state);
>> ÂÂÂÂÂÂÂÂÂ }
>> ÂÂÂÂÂ }
>> +ÂÂÂ if (!vq->packed_ring)
>> +ÂÂÂÂÂÂÂ 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
> 
> 
>> ÂÂÂÂÂ list_del(&_vq->list);
>> ÂÂÂÂÂ kfree(vq);
>> Â }
>