Re: [dpdk-dev] [PATCH] gro: add missing invalid packet checks

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

> 
> 
> > -----Original Message-----
> > From: Stephen Hemminger [mailto:stephen@networkplumber.org]
> > Sent: Tuesday, January 8, 2019 2:32 PM
> > To: Hu, Jiayu <jiayu.hu@intel.com>
> > Cc: dev@dpdk.org; Bie, Tiwei <tiwei.bie@intel.com>; Richardson, Bruce
> > <bruce.richardson@intel.com>; stable@dpdk.org
> > Subject: Re: [dpdk-dev] [PATCH] gro: add missing invalid packet checks
> >
> > On Tue,  8 Jan 2019 14:08:45 +0800
> > Jiayu Hu <jiayu.hu@intel.com> wrote:
> >
> > > +	/*
> > > +	 * Don't process the packet whose Ethernet, IPv4 and TCP header
> > > +	 * lengths are invalid. In addition, if the IPv4 header contains
> > > +	 * Options, the packet shouldn't be processed.
> > > +	 */
> > > +	if (unlikely(ILLEGAL_ETHER_HDRLEN(pkt->l2_len) ||
> > > +			ILLEGAL_IPV4_HDRLEN(pkt->l3_len) ||
> > > +			ILLEGAL_TCP_HDRLEN(pkt->l4_len)))
> > > +		return -1;
> 
> In the GRO design, we assume applications give correct
> MBUF->l2_len/.. for input packets of GRO. Specifically, GRO
> library assumes applications will set values to MBUF->l2_len/...
> and guarantee the values are the same as the values in the packet
> headers. The reason for this assumption is to process header faster.
> This is also why I want to add this assumption in the programmer
> guide.
> 
> The above code is to forbid GRO to process invalid packets, which
> have invalid packet header lengths, like TCP header length is less than
> 20 bytes.
> 
> >
> > I like it when code is as picky as possible when doing optimizations because
> > it reduces possible security riskg.
> >
> > To me this looks more confusing and not as careful as doing it like:
> >
> > 	if (unlikely(pkt->l2_len != ETHER_HDR_LEN))
> > 		return -1;
> > 	eth_hdr = rte_pktmbuf_mtod(pkt, struct ether_hdr *);
> > 	ipv4_hdr = (struct ipv4_hdr *)((char *)eth_hdr + ETHER_HDR_LEN);
> >
> > 	if (pkt->l3_len != (ipv4->version_ihl & IPV4_HDR_IHL_MASK) << 4)
> > 		return -1;
> >
> > 	if (pkt->l4_len < sizeof(struct tcp_hdr))
> > 		return -1;
> >
> > You should also check for TCP options as well.
> 
> There are two ways to get ether, ipv4 and tcp headers:
> 1). Use MBUF->l2_len/l3_len...;
> 2). Parse packet and ignore MBUF->l2_len/....
> 
> If we follow the choice 1, we don't need to parse packet and
> don't need to check if values of MBUF->l2_len/... are correct,
> since we assume applications will set correct values. If we follow
> the choice 2, we don't need to care about the values of MBUF->l2_len/...
> 
> I am a little confused about your code, since it parses packet and
> checks if the values of MBUF->l2_len/... are correct. If we don't use
> MBUF->l2_len/... to get ether/ipv4/tcp headers, why should we check
> the values of MBUF->l2_len/...?
> 

Agree that we don't need both.
My preference would be to stick with 1).
In many cases user would have already determined l2/l3/l4 len
by this stage.
Konstantin