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Date: Fri, 26 Jun 2020 08:39:53 -0700
From: Tom Herbert <tom@...bertland.com>
To: Justin Iurman <justin.iurman@...ege.be>
Cc: Linux Kernel Network Developers <netdev@...r.kernel.org>,
"David S. Miller" <davem@...emloft.net>
Subject: Re: [PATCH net-next 1/5] ipv6: eh: Introduce removable TLVs
On Fri, Jun 26, 2020 at 1:22 AM Justin Iurman <justin.iurman@...ege.be> wrote:
>
> Tom,
>
> >> Hi Tom,
> >>
> >> >> Add the possibility to remove one or more consecutive TLVs without
> >> >> messing up the alignment of others. For now, only IOAM requires this
> >> >> behavior.
> >> >>
> >> > Hi Justin,
> >> >
> >> > Can you explain the motivation for this? Per RFC8200, extension
> >> > headers in flight are not to be added, removed, or modified outside of
> >> > the standard rules for processing modifiable HBH and DO TLVs., that
> >> > would include adding and removing TLVs in EH. One obvious problem this
> >>
> >> As you already know from our last meeting, IOAM may be configured on a node such
> >> that a specific IOAM namespace should be removed. Therefore, this patch
> >> provides support for the deletion of a TLV (or consecutive TLVs), without
> >> removing the entire EH (if it's empty, there will be padding). Note that there
> >> is a similar "problem" with the Incremental Trace where you'd need to expand
> >> the Hop-by-Hop (not included in this patchset). I agree that RFC 8200 is
> >> against modification of in-flight EHs, but there are several reasons that, I
> >> believe, mitigates this statement.
> >>
> >> Let's keep in mind that IOAM purpose is "private" (= IOAM domain), ie not widely
> >> deployed on the Internet. We can distinguish two big scenarios: (i) in-transit
> >> traffic where it is encapsulated (IPv6-in-IPv6) and (ii) traffic inside the
> >> domain, ie from an IOAM node inside the domain to another one (no need for
> >> encapsulation). In both cases, we kind of own the traffic: (i) encapsulation,
> >> so we modify "our" header and (ii) we already own the traffic.
> >>
> >> And if someone is still angry about this, well, the good news is that such
> >> modification can be avoided most of the time. Indeed, operators are advised to
> >> remove an IOAM namespace only on egress nodes. This way, the destination
> >> (either the tunnel destination or the real destination, depending on the
> >> scenario) will receive EHs and take care of them without the need to remove
> >> anything. But, again, operators can do what they want and I'd tend to adhere to
> >> David's philosophy [1] and give them the possibility to choose what to do.
> >>
> >
> > Justin,
> >
> > 6man WG has had a _long_ and sometimes bitter discussion around this
> > particularly with regards to insertion of SRH. The current consensus
> > of IETF is that it is a violation of RFC8200. We've heard all the
> > arguments that it's only for limited domains and narrow use cases,
> > nevertheless there are several problems that the header
> > insertion/deletion advocates never answered-- it breaks AH, it breaks
> > PMTU discovery, it breaks ICMP. There is also a risk that a
> > non-standard modification could cause a packet to be dropped
> > downstream from the node that modifies it. There is no attribution on
> > who created the problem, and hence this can lead to systematic
> > blackholes which are the most miserable sort of problem to debug.
>
> Yes, I know the whole story and it's been stormy from what I understood.
>
> > Fundamentally, it is not robust per Postel's law (I actually wrote a
> > draft to try to make it robust in draft-herbert-6man-eh-attrib-00 if
> > you're interested).
>
> Interesting, I'll take a look.
>
> > IMO, we shouldn't be using Linux as a backdoor to implement protocol
> > that IETF is saying isn't robust. Can you point out in the IOAM drafts
> > where this requirement is specified, then I can take it up in IOAM WG
> > or 6man if needed...
>
> Well, I wouldn't say that IETF is considering IPv6-IOAM as not robust since [1] (IPv6 encapsulation for IOAM) and [2] (IOAM data fields) are about to be published.
I was specifically referring to the requirements around removing the
IOAM TLV from packets in-flight. I don't readily see that in the IOAM
drafts.
Also, be careful about saying that drafts are about to be published by
IETF. Until a draft reaches the RFC editor we really can't say that. I
don't believe drafts you're referring to have even made it through
WGLC.
Tom
>
> Justin
>
> [1] https://tools.ietf.org/html/draft-ietf-ippm-ioam-ipv6-options-01
> [2] https://tools.ietf.org/html/draft-ietf-ippm-ioam-data-09
>
> > Tom
> >
> >> > creates is that it breaks AH if the TLVs are removed in HBH before AH
> >> > is processed (AH is processed after HBH).
> >>
> >> Correct. But I don't think it should prevent us from having IOAM in the kernel.
> >> Again, operators could simply apply IOAM on a subset of the traffic that does
> >> not include AHs, for example.
> >>
> >> Justin
> >>
> >> [1] https://www.mail-archive.com/netdev@vger.kernel.org/msg136797.html
> >>
> >> > Tom
> >> >> By default, an 8-octet boundary is automatically assumed. This is the
> >> >> price to pay (at most a useless 4-octet padding) to make sure everything
> >> >> is still aligned after the removal.
> >> >>
> >> >> Proof: let's assume for instance the following alignments 2n, 4n and 8n
> >> >> respectively for options X, Y and Z, inside a Hop-by-Hop extension
> >> >> header.
> >> >>
> >> >> Example 1:
> >> >>
> >> >> +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
> >> >> | Next header | Hdr Ext Len | X | X |
> >> >> +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
> >> >> | X | X | Padding | Padding |
> >> >> +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
> >> >> | |
> >> >> ~ Option to be removed (8 octets) ~
> >> >> | |
> >> >> +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
> >> >> | Y | Y | Y | Y |
> >> >> +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
> >> >> | Padding | Padding | Padding | Padding |
> >> >> +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
> >> >> | Z | Z | Z | Z |
> >> >> +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
> >> >> | Z | Z | Z | Z |
> >> >> +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
> >> >>
> >> >> Result 1: assuming a 4-octet boundary would work, as well as an 8-octet
> >> >> boundary (same result in both cases).
> >> >>
> >> >> +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
> >> >> | Next header | Hdr Ext Len | X | X |
> >> >> +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
> >> >> | X | X | Padding | Padding |
> >> >> +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
> >> >> | Y | Y | Y | Y |
> >> >> +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
> >> >> | Padding | Padding | Padding | Padding |
> >> >> +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
> >> >> | Z | Z | Z | Z |
> >> >> +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
> >> >> | Z | Z | Z | Z |
> >> >> +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
> >> >>
> >> >> Example 2:
> >> >>
> >> >> +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
> >> >> | Next header | Hdr Ext Len | X | X |
> >> >> +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
> >> >> | X | X | Padding | Padding |
> >> >> +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
> >> >> | Option to be removed (4 octets) |
> >> >> +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
> >> >> | Y | Y | Y | Y |
> >> >> +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
> >> >> | Z | Z | Z | Z |
> >> >> +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
> >> >> | Z | Z | Z | Z |
> >> >> +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
> >> >>
> >> >> Result 2: assuming a 4-octet boundary WOULD NOT WORK. Indeed, option Z
> >> >> would not be 8n-aligned and the Hop-by-Hop size would not be a multiple
> >> >> of 8 anymore.
> >> >>
> >> >> +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
> >> >> | Next header | Hdr Ext Len | X | X |
> >> >> +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
> >> >> | X | X | Padding | Padding |
> >> >> +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
> >> >> | Y | Y | Y | Y |
> >> >> +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
> >> >> | Z | Z | Z | Z |
> >> >> +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
> >> >> | Z | Z | Z | Z |
> >> >> +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
> >> >>
> >> >> Therefore, the largest (8-octet) boundary is assumed by default and for
> >> >> all, which means that blocks are only moved in multiples of 8. This
> >> >> assertion guarantees good alignment.
> >> >>
> >> >> Signed-off-by: Justin Iurman <justin.iurman@...ege.be>
> >> >> ---
> >> >> net/ipv6/exthdrs.c | 134 ++++++++++++++++++++++++++++++++++++---------
> >> >> 1 file changed, 108 insertions(+), 26 deletions(-)
> >> >>
> >> >> diff --git a/net/ipv6/exthdrs.c b/net/ipv6/exthdrs.c
> >> >> index e9b366994475..f27ab3bf2e0c 100644
> >> >> --- a/net/ipv6/exthdrs.c
> >> >> +++ b/net/ipv6/exthdrs.c
> >> >> @@ -52,17 +52,27 @@
> >> >>
> >> >> #include <linux/uaccess.h>
> >> >>
> >> >> -/*
> >> >> - * Parsing tlv encoded headers.
> >> >> +/* States for TLV parsing functions. */
> >> >> +
> >> >> +enum {
> >> >> + TLV_ACCEPT,
> >> >> + TLV_REJECT,
> >> >> + TLV_REMOVE,
> >> >> + __TLV_MAX
> >> >> +};
> >> >> +
> >> >> +/* Parsing TLV encoded headers.
> >> >> *
> >> >> - * Parsing function "func" returns true, if parsing succeed
> >> >> - * and false, if it failed.
> >> >> - * It MUST NOT touch skb->h.
> >> >> + * Parsing function "func" returns either:
> >> >> + * - TLV_ACCEPT if parsing succeeds
> >> >> + * - TLV_REJECT if parsing fails
> >> >> + * - TLV_REMOVE if TLV must be removed
> >> >> + * It MUST NOT touch skb->h.
> >> >> */
> >> >>
> >> >> struct tlvtype_proc {
> >> >> int type;
> >> >> - bool (*func)(struct sk_buff *skb, int offset);
> >> >> + int (*func)(struct sk_buff *skb, int offset);
> >> >> };
> >> >>
> >> >> /*********************
> >> >> @@ -109,19 +119,67 @@ static bool ip6_tlvopt_unknown(struct sk_buff *skb, int
> >> >> optoff,
> >> >> return false;
> >> >> }
> >> >>
> >> >> +/* Remove one or several consecutive TLVs and recompute offsets, lengths */
> >> >> +
> >> >> +static int remove_tlv(int start, int end, struct sk_buff *skb)
> >> >> +{
> >> >> + int len = end - start;
> >> >> + int padlen = len % 8;
> >> >> + unsigned char *h;
> >> >> + int rlen, off;
> >> >> + u16 pl_len;
> >> >> +
> >> >> + rlen = len - padlen;
> >> >> + if (rlen) {
> >> >> + skb_pull(skb, rlen);
> >> >> + memmove(skb_network_header(skb) + rlen, skb_network_header(skb),
> >> >> + start);
> >> >> + skb_postpull_rcsum(skb, skb_network_header(skb), rlen);
> >> >> +
> >> >> + skb_reset_network_header(skb);
> >> >> + skb_set_transport_header(skb, sizeof(struct ipv6hdr));
> >> >> +
> >> >> + pl_len = be16_to_cpu(ipv6_hdr(skb)->payload_len) - rlen;
> >> >> + ipv6_hdr(skb)->payload_len = cpu_to_be16(pl_len);
> >> >> +
> >> >> + skb_transport_header(skb)[1] -= rlen >> 3;
> >> >> + end -= rlen;
> >> >> + }
> >> >> +
> >> >> + if (padlen) {
> >> >> + off = end - padlen;
> >> >> + h = skb_network_header(skb);
> >> >> +
> >> >> + if (padlen == 1) {
> >> >> + h[off] = IPV6_TLV_PAD1;
> >> >> + } else {
> >> >> + padlen -= 2;
> >> >> +
> >> >> + h[off] = IPV6_TLV_PADN;
> >> >> + h[off + 1] = padlen;
> >> >> + memset(&h[off + 2], 0, padlen);
> >> >> + }
> >> >> + }
> >> >> +
> >> >> + return end;
> >> >> +}
> >> >> +
> >> >> /* Parse tlv encoded option header (hop-by-hop or destination) */
> >> >>
> >> >> static bool ip6_parse_tlv(const struct tlvtype_proc *procs,
> >> >> struct sk_buff *skb,
> >> >> - int max_count)
> >> >> + int max_count,
> >> >> + bool removable)
> >> >> {
> >> >> int len = (skb_transport_header(skb)[1] + 1) << 3;
> >> >> - const unsigned char *nh = skb_network_header(skb);
> >> >> + unsigned char *nh = skb_network_header(skb);
> >> >> int off = skb_network_header_len(skb);
> >> >> const struct tlvtype_proc *curr;
> >> >> bool disallow_unknowns = false;
> >> >> + int off_remove = 0;
> >> >> int tlv_count = 0;
> >> >> int padlen = 0;
> >> >> + int ret;
> >> >>
> >> >> if (unlikely(max_count < 0)) {
> >> >> disallow_unknowns = true;
> >> >> @@ -173,12 +231,14 @@ static bool ip6_parse_tlv(const struct tlvtype_proc
> >> >> *procs,
> >> >> if (tlv_count > max_count)
> >> >> goto bad;
> >> >>
> >> >> + ret = -1;
> >> >> for (curr = procs; curr->type >= 0; curr++) {
> >> >> if (curr->type == nh[off]) {
> >> >> /* type specific length/alignment
> >> >> checks will be performed in the
> >> >> func(). */
> >> >> - if (curr->func(skb, off) == false)
> >> >> + ret = curr->func(skb, off);
> >> >> + if (ret == TLV_REJECT)
> >> >> return false;
> >> >> break;
> >> >> }
> >> >> @@ -187,6 +247,17 @@ static bool ip6_parse_tlv(const struct tlvtype_proc *procs,
> >> >> !ip6_tlvopt_unknown(skb, off, disallow_unknowns))
> >> >> return false;
> >> >>
> >> >> + if (removable) {
> >> >> + if (ret == TLV_REMOVE) {
> >> >> + if (!off_remove)
> >> >> + off_remove = off - padlen;
> >> >> + } else if (off_remove) {
> >> >> + off = remove_tlv(off_remove, off, skb);
> >> >> + nh = skb_network_header(skb);
> >> >> + off_remove = 0;
> >> >> + }
> >> >> + }
> >> >> +
> >> >> padlen = 0;
> >> >> break;
> >> >> }
> >> >> @@ -194,8 +265,13 @@ static bool ip6_parse_tlv(const struct tlvtype_proc *procs,
> >> >> len -= optlen;
> >> >> }
> >> >>
> >> >> - if (len == 0)
> >> >> + if (len == 0) {
> >> >> + /* Don't forget last TLV if it must be removed */
> >> >> + if (off_remove)
> >> >> + remove_tlv(off_remove, off, skb);
> >> >> +
> >> >> return true;
> >> >> + }
> >> >> bad:
> >> >> kfree_skb(skb);
> >> >> return false;
> >> >> @@ -206,7 +282,7 @@ static bool ip6_parse_tlv(const struct tlvtype_proc *procs,
> >> >> *****************************/
> >> >>
> >> >> #if IS_ENABLED(CONFIG_IPV6_MIP6)
> >> >> -static bool ipv6_dest_hao(struct sk_buff *skb, int optoff)
> >> >> +static int ipv6_dest_hao(struct sk_buff *skb, int optoff)
> >> >> {
> >> >> struct ipv6_destopt_hao *hao;
> >> >> struct inet6_skb_parm *opt = IP6CB(skb);
> >> >> @@ -257,11 +333,11 @@ static bool ipv6_dest_hao(struct sk_buff *skb, int optoff)
> >> >> if (skb->tstamp == 0)
> >> >> __net_timestamp(skb);
> >> >>
> >> >> - return true;
> >> >> + return TLV_ACCEPT;
> >> >>
> >> >> discard:
> >> >> kfree_skb(skb);
> >> >> - return false;
> >> >> + return TLV_REJECT;
> >> >> }
> >> >> #endif
> >> >>
> >> >> @@ -306,7 +382,8 @@ static int ipv6_destopt_rcv(struct sk_buff *skb)
> >> >> #endif
> >> >>
> >> >> if (ip6_parse_tlv(tlvprocdestopt_lst, skb,
> >> >> - init_net.ipv6.sysctl.max_dst_opts_cnt)) {
> >> >> + init_net.ipv6.sysctl.max_dst_opts_cnt,
> >> >> + false)) {
> >> >> skb->transport_header += extlen;
> >> >> opt = IP6CB(skb);
> >> >> #if IS_ENABLED(CONFIG_IPV6_MIP6)
> >> >> @@ -918,24 +995,24 @@ static inline struct net *ipv6_skb_net(struct sk_buff
> >> >> *skb)
> >> >>
> >> >> /* Router Alert as of RFC 2711 */
> >> >>
> >> >> -static bool ipv6_hop_ra(struct sk_buff *skb, int optoff)
> >> >> +static int ipv6_hop_ra(struct sk_buff *skb, int optoff)
> >> >> {
> >> >> const unsigned char *nh = skb_network_header(skb);
> >> >>
> >> >> if (nh[optoff + 1] == 2) {
> >> >> IP6CB(skb)->flags |= IP6SKB_ROUTERALERT;
> >> >> memcpy(&IP6CB(skb)->ra, nh + optoff + 2, sizeof(IP6CB(skb)->ra));
> >> >> - return true;
> >> >> + return TLV_ACCEPT;
> >> >> }
> >> >> net_dbg_ratelimited("ipv6_hop_ra: wrong RA length %d\n",
> >> >> nh[optoff + 1]);
> >> >> kfree_skb(skb);
> >> >> - return false;
> >> >> + return TLV_REJECT;
> >> >> }
> >> >>
> >> >> /* Jumbo payload */
> >> >>
> >> >> -static bool ipv6_hop_jumbo(struct sk_buff *skb, int optoff)
> >> >> +static int ipv6_hop_jumbo(struct sk_buff *skb, int optoff)
> >> >> {
> >> >> const unsigned char *nh = skb_network_header(skb);
> >> >> struct inet6_dev *idev = __in6_dev_get_safely(skb->dev);
> >> >> @@ -953,12 +1030,12 @@ static bool ipv6_hop_jumbo(struct sk_buff *skb, int
> >> >> optoff)
> >> >> if (pkt_len <= IPV6_MAXPLEN) {
> >> >> __IP6_INC_STATS(net, idev, IPSTATS_MIB_INHDRERRORS);
> >> >> icmpv6_param_prob(skb, ICMPV6_HDR_FIELD, optoff+2);
> >> >> - return false;
> >> >> + return TLV_REJECT;
> >> >> }
> >> >> if (ipv6_hdr(skb)->payload_len) {
> >> >> __IP6_INC_STATS(net, idev, IPSTATS_MIB_INHDRERRORS);
> >> >> icmpv6_param_prob(skb, ICMPV6_HDR_FIELD, optoff);
> >> >> - return false;
> >> >> + return TLV_REJECT;
> >> >> }
> >> >>
> >> >> if (pkt_len > skb->len - sizeof(struct ipv6hdr)) {
> >> >> @@ -970,16 +1047,16 @@ static bool ipv6_hop_jumbo(struct sk_buff *skb, int
> >> >> optoff)
> >> >> goto drop;
> >> >>
> >> >> IP6CB(skb)->flags |= IP6SKB_JUMBOGRAM;
> >> >> - return true;
> >> >> + return TLV_ACCEPT;
> >> >>
> >> >> drop:
> >> >> kfree_skb(skb);
> >> >> - return false;
> >> >> + return TLV_REJECT;
> >> >> }
> >> >>
> >> >> /* CALIPSO RFC 5570 */
> >> >>
> >> >> -static bool ipv6_hop_calipso(struct sk_buff *skb, int optoff)
> >> >> +static int ipv6_hop_calipso(struct sk_buff *skb, int optoff)
> >> >> {
> >> >> const unsigned char *nh = skb_network_header(skb);
> >> >>
> >> >> @@ -992,11 +1069,11 @@ static bool ipv6_hop_calipso(struct sk_buff *skb, int
> >> >> optoff)
> >> >> if (!calipso_validate(skb, nh + optoff))
> >> >> goto drop;
> >> >>
> >> >> - return true;
> >> >> + return TLV_ACCEPT;
> >> >>
> >> >> drop:
> >> >> kfree_skb(skb);
> >> >> - return false;
> >> >> + return TLV_REJECT;
> >> >> }
> >> >>
> >> >> static const struct tlvtype_proc tlvprochopopt_lst[] = {
> >> >> @@ -1041,7 +1118,12 @@ int ipv6_parse_hopopts(struct sk_buff *skb)
> >> >>
> >> >> opt->flags |= IP6SKB_HOPBYHOP;
> >> >> if (ip6_parse_tlv(tlvprochopopt_lst, skb,
> >> >> - init_net.ipv6.sysctl.max_hbh_opts_cnt)) {
> >> >> + init_net.ipv6.sysctl.max_hbh_opts_cnt,
> >> >> + true)) {
> >> >> + /* we need to refresh the length in case
> >> >> + * at least one TLV was removed
> >> >> + */
> >> >> + extlen = (skb_transport_header(skb)[1] + 1) << 3;
> >> >> skb->transport_header += extlen;
> >> >> opt = IP6CB(skb);
> >> >> opt->nhoff = sizeof(struct ipv6hdr);
> >> >> --
> > > >> 2.17.1
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