[dpdk-dev] [PATCH] vhost: fix off-by-one error on nr_desc check

[dpdk-dev] [PATCH] vhost: fix off-by-one error on nr_desc check

[Maxime Coquelin]

nr_desc is not an index but the number of descriptors,
so can be equal to the virtqueue size.

Fixes: a436f53ebfeb ("vhost: avoid dead loop chain")

Cc: Yuanhan Liu <yuanhan.liu@linux.intel.com>
Signed-off-by: Maxime Coquelin <maxime.coquelin@redhat.com>
---
Hi Yuanhan,

I faced the bug while testing my indirect descriptor patch, it happens
as soon as the number of chained descritors is above 2.

But the bug may in theory also be faced with normal descriptors, so it might
be good to have it 16.07?

Regards,
Maxime

---
 lib/librte_vhost/vhost_rxtx.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/lib/librte_vhost/vhost_rxtx.c b/lib/librte_vhost/vhost_rxtx.c
index bc00518..08a73fd 100644
--- a/lib/librte_vhost/vhost_rxtx.c
+++ b/lib/librte_vhost/vhost_rxtx.c
@@ -748,7 +748,7 @@ copy_desc_to_mbuf(struct virtio_net *dev, struct vhost_virtqueue *vq,
 				break;
 
 			if (unlikely(desc->next >= vq->size ||
-				     ++nr_desc >= vq->size))
+				     ++nr_desc > vq->size))
 				return -1;
 			desc = &vq->desc[desc->next];
 
-- 
2.7.4

Re: [dpdk-dev] [PATCH] vhost: fix off-by-one error on nr_desc check

[Yuanhan Liu]

On Mon, Jul 25, 2016 at 04:09:58PM +0200, Maxime Coquelin wrote:
> nr_desc is not an index but the number of descriptors,
> so can be equal to the virtqueue size.
> 
> Fixes: a436f53ebfeb ("vhost: avoid dead loop chain")
> 
> Cc: Yuanhan Liu <yuanhan.liu@linux.intel.com>
> Signed-off-by: Maxime Coquelin <maxime.coquelin@redhat.com>

Thanks for catching it!

> ---
> Hi Yuanhan,
> 
> I faced the bug while testing my indirect descriptor patch, it happens
> as soon as the number of chained descritors is above 2.
> 
> But the bug may in theory also be faced with normal descriptors,

In theory, yes, and only in one case, that there is a Tx has 256
descriptors chained. If that happens, I doubt things work well.
So I would say it just happens __in theory__.

> so it might
> be good to have it 16.07?

Even though, it apparently fixes a bug, so I think we could have it
for 16.07.

Acked-by: Yuanhan Liu <yuanhan.liu@linux.intel.com>

	--yliu

Re: [dpdk-dev] [PATCH] vhost: fix off-by-one error on nr_desc check

[Maxime Coquelin]

On 07/25/2016 05:24 PM, Yuanhan Liu wrote:
> On Mon, Jul 25, 2016 at 04:09:58PM +0200, Maxime Coquelin wrote:
>> nr_desc is not an index but the number of descriptors,
>> so can be equal to the virtqueue size.
>>
>> Fixes: a436f53ebfeb ("vhost: avoid dead loop chain")
>>
>> Cc: Yuanhan Liu <yuanhan.liu@linux.intel.com>
>> Signed-off-by: Maxime Coquelin <maxime.coquelin@redhat.com>
>
> Thanks for catching it!
>
>> ---
>> Hi Yuanhan,
>>
>> I faced the bug while testing my indirect descriptor patch, it happens
>> as soon as the number of chained descritors is above 2.
>>
>> But the bug may in theory also be faced with normal descriptors,
>
> In theory, yes, and only in one case, that there is a Tx has 256
> descriptors chained. If that happens, I doubt things work well.
> So I would say it just happens __in theory__.
Right.

>
>> so it might
>> be good to have it 16.07?
>
> Even though, it apparently fixes a bug, so I think we could have it
> for 16.07.
Good, but don't delay 16.07 for that! :)

>
> Acked-by: Yuanhan Liu <yuanhan.liu@linux.intel.com>
>
> 	--yliu
>

Thanks,
Maxime

Re: [dpdk-dev] [PATCH] vhost: fix off-by-one error on nr_desc check

[Thomas Monjalon]

2016-07-25 23:24, Yuanhan Liu:
> On Mon, Jul 25, 2016 at 04:09:58PM +0200, Maxime Coquelin wrote:
> > nr_desc is not an index but the number of descriptors,
> > so can be equal to the virtqueue size.
> > 
> > Fixes: a436f53ebfeb ("vhost: avoid dead loop chain")
> > 
> > Cc: Yuanhan Liu <yuanhan.liu@linux.intel.com>
> > Signed-off-by: Maxime Coquelin <maxime.coquelin@redhat.com>
> 
> Thanks for catching it!
> 
> > ---
> > Hi Yuanhan,
> > 
> > I faced the bug while testing my indirect descriptor patch, it happens
> > as soon as the number of chained descritors is above 2.
> > 
> > But the bug may in theory also be faced with normal descriptors,
> 
> In theory, yes, and only in one case, that there is a Tx has 256
> descriptors chained. If that happens, I doubt things work well.
> So I would say it just happens __in theory__.
> 
> > so it might
> > be good to have it 16.07?
> 
> Even though, it apparently fixes a bug, so I think we could have it
> for 16.07.
> 
> Acked-by: Yuanhan Liu <yuanhan.liu@linux.intel.com>

Applied, thanks