Re: [PATCH v2] vhost: fix segfault on bad descriptor address

[Yuanhan Liu <yuanhan.liu@linux.intel.com>]

On Fri, Jul 15, 2016 at 10:23:12AM +0300, Ilya Maximets wrote:
> On 15.07.2016 09:17, Yuanhan Liu wrote:
> > On Thu, Jul 14, 2016 at 11:18:39AM +0300, Ilya Maximets wrote:
> >> In current implementation vhost will crash with segmentation fault
> >> if malicious or buggy virtio application breaks addresses of descriptors.
> >>
> >> Before commit 0823c1cb0a73 this crash was reproducible even with
> >> normal DPDK application that tries to change number of virtqueues
> >> dynamically inside VM.
> >>
> >> Fix that by checking addresses of descriptors before using.
> >>
> >> Also fixed return value on error for 'copy_mbuf_to_desc_mergeable()'
> >> from '-1' to '0' because it returns unsigned value and it means
> >> number of used descriptors.
> > 
> > Yeah, that's a good fix. Thanks.
> > 
> > Maybe you'd better make it a standalone patch.
> 
> Ok. Maybe I should split this patch in two:
> 1. Fix return value + using of this value (vq->last_used_idx += nr_used;)
> 2. Check addresses of descriptors.
> What do you think?

Good to me.

> >> Signed-off-by: Ilya Maximets <i.maximets@samsung.com>
> >> ---
> >> Version 2:
> >> 	* Rebased on top of current master.
> >> 	* host's address now checked in meargeable case,
> >> 	  because needed refactoring already done.
> >> 	* Commit-message changed because old issue with
> >> 	  virtio reload accidentially fixed by commit
> >> 	  0823c1cb0a73.
> >>
> >>  lib/librte_vhost/vhost_rxtx.c | 28 +++++++++++++++++++++-------
> >>  1 file changed, 21 insertions(+), 7 deletions(-)
> >>
> >> diff --git a/lib/librte_vhost/vhost_rxtx.c b/lib/librte_vhost/vhost_rxtx.c
> >> index 15ca956..31e8b58 100644
> >> --- a/lib/librte_vhost/vhost_rxtx.c
> >> +++ b/lib/librte_vhost/vhost_rxtx.c
> >> @@ -147,10 +147,10 @@ copy_mbuf_to_desc(struct virtio_net *dev, struct vhost_virtqueue *vq,
> >>  	struct virtio_net_hdr_mrg_rxbuf virtio_hdr = {{0, 0, 0, 0, 0, 0}, 0};
> >>  
> >>  	desc = &vq->desc[desc_idx];
> >> -	if (unlikely(desc->len < dev->vhost_hlen))
> >> +	desc_addr = gpa_to_vva(dev, desc->addr);
> >> +	if (unlikely(desc->len < dev->vhost_hlen || !desc_addr))
> >>  		return -1;
> > 
> > So, you discards the workaround from Rich?
> 
> I can apply it, if you wish. Should I?

Yeah, it's hard to tell. The performace regression is weird after all.
I'm thinking we should appy it anyway: it saves 10% regression, which
is worthwhile. I think we should also add comments there.

	--yliu