[PATCH net-next] ip6_tunnel: Fix missing tunnel encapsulation limit option

[PATCH net-next] ip6_tunnel: Fix missing tunnel encapsulation limit option

[Craig Gallek]

From: Craig Gallek <kraig@google.com>

The IPv6 tunneling code tries to insert IPV6_TLV_TNL_ENCAP_LIMIT and
IPV6_TLV_PADN options when an encapsulation limit is defined (the
default is a limit of 4).  An MTU adjustment is done to account for
these options as well.  However, the options are never present in the
generated packets.

ipv6_push_nfrag_opts requires that IPV6_RTHDR be present in order to
include any IPV6_DSTOPTS options.  The v6 tunnel code does not
use routing options, so the encap limit options are not included.

A brief reading of RFC 3542 section 9.2 (specifically the 4th paragraph)
makes me believe that this requirement in the kernel is incorrect.

Fixes: 333fad5364d6: ("[IPV6]: Support several new sockopt / ancillary data in Advanced API (RFC3542)")
Signed-off-by: Craig Gallek <kraig@google.com>
---
 net/ipv6/exthdrs.c | 13 +++++--------
 1 file changed, 5 insertions(+), 8 deletions(-)

diff --git a/net/ipv6/exthdrs.c b/net/ipv6/exthdrs.c
index 25192a3b0cd7..224a89e68a42 100644
--- a/net/ipv6/exthdrs.c
+++ b/net/ipv6/exthdrs.c
@@ -932,15 +932,12 @@ void ipv6_push_nfrag_opts(struct sk_buff *skb, struct ipv6_txoptions *opt,
 			  u8 *proto,
 			  struct in6_addr **daddr, struct in6_addr *saddr)
 {
-	if (opt->srcrt) {
+	if (opt->srcrt)
 		ipv6_push_rthdr(skb, proto, opt->srcrt, daddr, saddr);
-		/*
-		 * IPV6_RTHDRDSTOPTS is ignored
-		 * unless IPV6_RTHDR is set (RFC3542).
-		 */
-		if (opt->dst0opt)
-			ipv6_push_exthdr(skb, proto, NEXTHDR_DEST, opt->dst0opt);
-	}
+
+	if (opt->dst0opt)
+		ipv6_push_exthdr(skb, proto, NEXTHDR_DEST, opt->dst0opt);
+
 	if (opt->hopopt)
 		ipv6_push_exthdr(skb, proto, NEXTHDR_HOP, opt->hopopt);
 }
-- 
2.13.0.rc0.306.g87b477812d-goog

Re: [PATCH net-next] ip6_tunnel: Fix missing tunnel encapsulation limit option

[Craig Gallek]

On Wed, Apr 26, 2017 at 1:07 PM, Craig Gallek <kraigatgoog@gmail.com> wrote:
> From: Craig Gallek <kraig@google.com>
>
> The IPv6 tunneling code tries to insert IPV6_TLV_TNL_ENCAP_LIMIT and
> IPV6_TLV_PADN options when an encapsulation limit is defined (the
> default is a limit of 4).  An MTU adjustment is done to account for
> these options as well.  However, the options are never present in the
> generated packets.
>
> ipv6_push_nfrag_opts requires that IPV6_RTHDR be present in order to
> include any IPV6_DSTOPTS options.  The v6 tunnel code does not
> use routing options, so the encap limit options are not included.
>
> A brief reading of RFC 3542 section 9.2 (specifically the 4th paragraph)
> makes me believe that this requirement in the kernel is incorrect.
Looking more closely, I think I'm wrong here.  Specifically, the cmsg
parser puts IPV6_RTHDRDSTOPTS in dst0opt and IPV6_DSTOPTS in dst1opt.
The tunnel code is currently building dst0opt and using
ipv6_push_nfrag_opts.  Perhaps it should be building dst1opt and
calling ipv6_push_frag_opts?

[PATCH v2 net-next] ip6_tunnel: Fix missing tunnel encapsulation limit option

[Craig Gallek]

From: Craig Gallek <cgallek@google.com>

The IPv6 tunneling code tries to insert IPV6_TLV_TNL_ENCAP_LIMIT and
IPV6_TLV_PADN options when an encapsulation limit is defined (the
default is a limit of 4).  An MTU adjustment is done to account for
these options as well.  However, the options are never present in the
generated packets.

The issue appears to be a subtlety between IPV6_DSTOPTS and
IPV6_RTHDRDSTOPTS defined in RFC 3542.  When the IPIP tunnel driver was
written, the encap limit options were included as IPV6_RTHDRDSTOPTS in
dst0opt of struct ipv6_txoptions.  Later, ipv6_push_nfrags_opts was
(correctly) updated to require IPV6_RTHDR options when IPV6_RTHDRDSTOPTS
are to be used.  This caused the options to no longer be included in v6
encapsulated packets.

The fix is to use IPV6_DSTOPTS (in dst1opt of struct ipv6_txoptions)
instead.  IPV6_DSTOPTS do not have the additional IPV6_RTHDR requirement.

Fixes: 1df64a8569c7: ("[IPV6]: Add ip6ip6 tunnel driver.")
Fixes: 333fad5364d6: ("[IPV6]: Support several new sockopt / ancillary data in Advanced API (RFC3542)")
Signed-off-by: Craig Gallek <kraig@google.com>
---

v2: Change tunnel code to use dst1opt rather than making the checks for
    dst0opt more permissive.

 net/ipv6/ip6_tunnel.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/net/ipv6/ip6_tunnel.c b/net/ipv6/ip6_tunnel.c
index ad15d38b41e8..c81f9541f1f7 100644
--- a/net/ipv6/ip6_tunnel.c
+++ b/net/ipv6/ip6_tunnel.c
@@ -954,7 +954,7 @@ static void init_tel_txopt(struct ipv6_tel_txoption *opt, __u8 encap_limit)
 	opt->dst_opt[5] = IPV6_TLV_PADN;
 	opt->dst_opt[6] = 1;
 
-	opt->ops.dst0opt = (struct ipv6_opt_hdr *) opt->dst_opt;
+	opt->ops.dst1opt = (struct ipv6_opt_hdr *) opt->dst_opt;
 	opt->ops.opt_nflen = 8;
 }
 
@@ -1176,7 +1176,7 @@ int ip6_tnl_xmit(struct sk_buff *skb, struct net_device *dev, __u8 dsfield,
 
 	if (encap_limit >= 0) {
 		init_tel_txopt(&opt, encap_limit);
-		ipv6_push_nfrag_opts(skb, &opt.ops, &proto, NULL, NULL);
+		ipv6_push_frag_opts(skb, &opt.ops, &proto);
 	}
 
 	/* Calculate max headroom for all the headers and adjust
-- 
2.13.0.rc0.306.g87b477812d-goog

Re: [PATCH v2 net-next] ip6_tunnel: Fix missing tunnel encapsulation limit option

[David Miller]

From: Craig Gallek <kraigatgoog@gmail.com>
Date: Wed, 26 Apr 2017 14:37:45 -0400

> From: Craig Gallek <cgallek@google.com>
> 
> The IPv6 tunneling code tries to insert IPV6_TLV_TNL_ENCAP_LIMIT and
> IPV6_TLV_PADN options when an encapsulation limit is defined (the
> default is a limit of 4).  An MTU adjustment is done to account for
> these options as well.  However, the options are never present in the
> generated packets.
> 
> The issue appears to be a subtlety between IPV6_DSTOPTS and
> IPV6_RTHDRDSTOPTS defined in RFC 3542.  When the IPIP tunnel driver was
> written, the encap limit options were included as IPV6_RTHDRDSTOPTS in
> dst0opt of struct ipv6_txoptions.  Later, ipv6_push_nfrags_opts was
> (correctly) updated to require IPV6_RTHDR options when IPV6_RTHDRDSTOPTS
> are to be used.  This caused the options to no longer be included in v6
> encapsulated packets.
> 
> The fix is to use IPV6_DSTOPTS (in dst1opt of struct ipv6_txoptions)
> instead.  IPV6_DSTOPTS do not have the additional IPV6_RTHDR requirement.
> 
> Fixes: 1df64a8569c7: ("[IPV6]: Add ip6ip6 tunnel driver.")
> Fixes: 333fad5364d6: ("[IPV6]: Support several new sockopt / ancillary data in Advanced API (RFC3542)")
> Signed-off-by: Craig Gallek <kraig@google.com>
> ---
> 
> v2: Change tunnel code to use dst1opt rather than making the checks for
>     dst0opt more permissive.

Thanks for the detailed analysis in the commit message, this made reviewing
your patch a lot easier.

Applied, thank you.