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From:   Cpp Code <cpp.code.lv@gmail.com>
Date:   Mon, 6 Dec 2021 15:00:40 -0800
Message-ID: <CAASuNyUKj+dsf++7mhdkjm2mabQggYW4x42_BV=y+VPPSBFqfA@mail.gmail.com>
Subject: Re: [PATCH net-next v8] net: openvswitch: IPv6: Add IPv6 extension
 header support
To:     Pravin Shelar <pravin.ovn@gmail.com>
Cc:     Linux Kernel Network Developers <netdev@vger.kernel.org>,
        "David S. Miller" <davem@davemloft.net>,
        Jakub Kicinski <kuba@kernel.org>,
        ovs dev <dev@openvswitch.org>,
        LKML <linux-kernel@vger.kernel.org>
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On Thu, Dec 2, 2021 at 9:28 PM Pravin Shelar <pravin.ovn@gmail.com> wrote:
>
> On Thu, Dec 2, 2021 at 12:20 PM Cpp Code <cpp.code.lv@gmail.com> wrote:
> >
> > On Wed, Dec 1, 2021 at 11:34 PM Pravin Shelar <pravin.ovn@gmail.com> wrote:
> > >
> > > On Wed, Nov 24, 2021 at 11:33 AM Toms Atteka <cpp.code.lv@gmail.com> wrote:
> > > >
> > > > This change adds a new OpenFlow field OFPXMT_OFB_IPV6_EXTHDR and
> > > > packets can be filtered using ipv6_ext flag.
> > > >
> > > > Signed-off-by: Toms Atteka <cpp.code.lv@gmail.com>
> > > > ---
> > > >  include/uapi/linux/openvswitch.h |   6 ++
> > > >  net/openvswitch/flow.c           | 140 +++++++++++++++++++++++++++++++
> > > >  net/openvswitch/flow.h           |  14 ++++
> > > >  net/openvswitch/flow_netlink.c   |  26 +++++-
> > > >  4 files changed, 184 insertions(+), 2 deletions(-)
> > > >
> > > > diff --git a/include/uapi/linux/openvswitch.h b/include/uapi/linux/openvswitch.h
> > > > index a87b44cd5590..43790f07e4a2 100644
> > > > --- a/include/uapi/linux/openvswitch.h
> > > > +++ b/include/uapi/linux/openvswitch.h
> > > > @@ -342,6 +342,7 @@ enum ovs_key_attr {
> > > >         OVS_KEY_ATTR_CT_ORIG_TUPLE_IPV4,   /* struct ovs_key_ct_tuple_ipv4 */
> > > >         OVS_KEY_ATTR_CT_ORIG_TUPLE_IPV6,   /* struct ovs_key_ct_tuple_ipv6 */
> > > >         OVS_KEY_ATTR_NSH,       /* Nested set of ovs_nsh_key_* */
> > > > +       OVS_KEY_ATTR_IPV6_EXTHDRS,  /* struct ovs_key_ipv6_exthdr */
> > > >
> > > >  #ifdef __KERNEL__
> > > >         OVS_KEY_ATTR_TUNNEL_INFO,  /* struct ip_tunnel_info */
> > > > @@ -421,6 +422,11 @@ struct ovs_key_ipv6 {
> > > >         __u8   ipv6_frag;       /* One of OVS_FRAG_TYPE_*. */
> > > >  };
> > > >
> > > > +/* separate structure to support backward compatibility with older user space */
> > > > +struct ovs_key_ipv6_exthdrs {
> > > > +       __u16  hdrs;
> > > > +};
> > > > +
> > > >  struct ovs_key_tcp {
> > > >         __be16 tcp_src;
> > > >         __be16 tcp_dst;
> > > > diff --git a/net/openvswitch/flow.c b/net/openvswitch/flow.c
> > > > index 9d375e74b607..28acb40437ca 100644
> > > > --- a/net/openvswitch/flow.c
> > > > +++ b/net/openvswitch/flow.c
> > > > @@ -239,6 +239,144 @@ static bool icmphdr_ok(struct sk_buff *skb)
> > > >                                   sizeof(struct icmphdr));
> > > >  }
> > > >
> > > > +/**
> > > > + * get_ipv6_ext_hdrs() - Parses packet and sets IPv6 extension header flags.
> > > > + *
> > > > + * @skb: buffer where extension header data starts in packet
> > > > + * @nh: ipv6 header
> > > > + * @ext_hdrs: flags are stored here
> > > > + *
> > > > + * OFPIEH12_UNREP is set if more than one of a given IPv6 extension header
> > > > + * is unexpectedly encountered. (Two destination options headers may be
> > > > + * expected and would not cause this bit to be set.)
> > > > + *
> > > > + * OFPIEH12_UNSEQ is set if IPv6 extension headers were not in the order
> > > > + * preferred (but not required) by RFC 2460:
> > > > + *
> > > > + * When more than one extension header is used in the same packet, it is
> > > > + * recommended that those headers appear in the following order:
> > > > + *      IPv6 header
> > > > + *      Hop-by-Hop Options header
> > > > + *      Destination Options header
> > > > + *      Routing header
> > > > + *      Fragment header
> > > > + *      Authentication header
> > > > + *      Encapsulating Security Payload header
> > > > + *      Destination Options header
> > > > + *      upper-layer header
> > > > + */
> > > > +static void get_ipv6_ext_hdrs(struct sk_buff *skb, struct ipv6hdr *nh,
> > > > +                             u16 *ext_hdrs)
> > > > +{
> > > > +       u8 next_type = nh->nexthdr;
> > > > +       unsigned int start = skb_network_offset(skb) + sizeof(struct ipv6hdr);
> > > > +       int dest_options_header_count = 0;
> > > > +
> > > > +       *ext_hdrs = 0;
> > > > +
> > > > +       while (ipv6_ext_hdr(next_type)) {
> > > > +               struct ipv6_opt_hdr _hdr, *hp;
> > > > +
> > > > +               switch (next_type) {
> > > > +               case IPPROTO_NONE:
> > > > +                       *ext_hdrs |= OFPIEH12_NONEXT;
> > > > +                       /* stop parsing */
> > > > +                       return;
> > > > +
> > > > +               case IPPROTO_ESP:
> > > > +                       if (*ext_hdrs & OFPIEH12_ESP)
> > > > +                               *ext_hdrs |= OFPIEH12_UNREP;
> > > > +                       if ((*ext_hdrs & ~(OFPIEH12_HOP | OFPIEH12_DEST |
> > > > +                                          OFPIEH12_ROUTER | IPPROTO_FRAGMENT |
> > > > +                                          OFPIEH12_AUTH | OFPIEH12_UNREP)) ||
> > > > +                           dest_options_header_count >= 2) {
> > > > +                               *ext_hdrs |= OFPIEH12_UNSEQ;
> > > > +                       }
> > > > +                       *ext_hdrs |= OFPIEH12_ESP;
> > > > +                       break;
> > > you need to check_header() before looking into each extension header.
> >
> > Could you elaborate why I need to add check_header(),
> > skb_header_pointer() is doing sanitization.
>
> I mean check_header() would allow you to read the header without
> copying the bits, it is used in ovs flow extraction so its usual
> check.

But check_header() will call *__pskb_pull_tail which in turn will copy
bits if data will be fragmented.

/* Moves tail of skb head forward, copying data from fragmented part,
 * when it is necessary.
 * 1. It may fail due to malloc failure.
 * 2. It may change skb pointers.
 *
 * It is pretty complicated. Luckily, it is called only in exceptional cases.
 */
void *__pskb_pull_tail(struct sk_buff *skb, int delta)

as well I noticed that for example commit
4a06fa67c4da20148803525151845276cdb995c1 is moving from
pskb_may_pull() to skb_header_pointer()