Re: [dpdk-stable] [PATCH v2] vhost: add header check in dequeue offload

["Ananyev, Konstantin" <konstantin.ananyev@intel.com>]

> -----Original Message-----
> From: David Marchand <david.marchand@redhat.com>
> Sent: Monday, March 15, 2021 4:17 PM
> To: Wang, Xiao W <xiao.w.wang@intel.com>
> Cc: Xia, Chenbo <chenbo.xia@intel.com>; Maxime Coquelin <maxime.coquelin@redhat.com>; Liu, Yong <yong.liu@intel.com>; dev
> <dev@dpdk.org>; Ananyev, Konstantin <konstantin.ananyev@intel.com>; dpdk stable <stable@dpdk.org>
> Subject: Re: [dpdk-stable] [PATCH v2] vhost: add header check in dequeue offload
> 
> On Mon, Mar 15, 2021 at 4:52 PM Xiao Wang <xiao.w.wang@intel.com> wrote:
> >
> > When parsing the virtio net header and packet header for dequeue offload,
> > we need to perform sanity check on the packet header to ensure:
> >   - No out-of-boundary memory access.
> >   - The packet header and virtio_net header are valid and aligned.
> >
> > Fixes: d0cf91303d73 ("vhost: add Tx offload capabilities")
> > Cc: stable@dpdk.org
> >
> > Signed-off-by: Xiao Wang <xiao.w.wang@intel.com>
> > ---
> > v2:
> > Allow empty L4 payload for cksum offload.
> > ---
> >  lib/librte_vhost/virtio_net.c | 49 +++++++++++++++++++++++++++++++++++++------
> >  1 file changed, 43 insertions(+), 6 deletions(-)
> >
> > diff --git a/lib/librte_vhost/virtio_net.c b/lib/librte_vhost/virtio_net.c
> > index 583bf379c6..53a8ff2898 100644
> > --- a/lib/librte_vhost/virtio_net.c
> > +++ b/lib/librte_vhost/virtio_net.c
> > @@ -1821,44 +1821,64 @@ virtio_net_with_host_offload(struct virtio_net *dev)
> >         return false;
> >  }
> >
> > -static void
> > -parse_ethernet(struct rte_mbuf *m, uint16_t *l4_proto, void **l4_hdr)
> > +static int
> > +parse_ethernet(struct rte_mbuf *m, uint16_t *l4_proto, void **l4_hdr,
> > +               uint16_t *len)
> >  {
> >         struct rte_ipv4_hdr *ipv4_hdr;
> >         struct rte_ipv6_hdr *ipv6_hdr;
> >         void *l3_hdr = NULL;
> >         struct rte_ether_hdr *eth_hdr;
> >         uint16_t ethertype;
> > +       uint16_t data_len = m->data_len;
> 
> >
> >         eth_hdr = rte_pktmbuf_mtod(m, struct rte_ether_hdr *);
> >
> > +       if (data_len <= sizeof(struct rte_ether_hdr))
> > +               return -EINVAL;
> 
> On principle, the check should happen before calling rte_pktmbuf_mtod,
> like what rte_pktmbuf_read does.
> 
> Looking at the rest of the patch, does this helper function only
> handle mono segment mbufs?
> My reading of copy_desc_to_mbuf() was that it could generate multi
> segments mbufs...
> 
> 
> [snip]
> 
> >         case RTE_ETHER_TYPE_IPV4:
> > +               if (data_len <= sizeof(struct rte_ipv4_hdr))
> > +                       return -EINVAL;
> >                 ipv4_hdr = l3_hdr;
> >                 *l4_proto = ipv4_hdr->next_proto_id;
> >                 m->l3_len = rte_ipv4_hdr_len(ipv4_hdr);
> > +               if (data_len <= m->l3_len) {
> > +                       m->l3_len = 0;
> > +                       return -EINVAL;
> > +               }
> 
> ... so here, comparing l3 length to only the first segment length
> (data_len) would be invalid.
> 
> If this helper must deal with multi segments, why not use rte_pktmbuf_read?
> This function returns access to mbuf data after checking offset and
> length are contiguous, else copy the needed data in a passed buffer.

From my understanding, yes multi-seg is allowed, but an expectation
Is that at least packet header (l2/l3/l4?) will always reside in first segment.

> 
> 
> >                 *l4_hdr = (char *)l3_hdr + m->l3_len;
> >                 m->ol_flags |= PKT_TX_IPV4;
> > +               data_len -= m->l3_len;
> >                 break;
> 
> 
> --
> David Marchand