compat: Fixup ipv6 fragmentation on 4.9.135+ kernels

Upstream commit 648700f76b03 ("inet: frags: use rhashtables...") changed
how ipv6 fragmentation is implemented.  This patch was backported to
the upstream stable 4.9.x kernel starting at 4.9.135.

This patch creates the compatibility layer changes required to both
compile and also operate correctly with ipv6 fragmentation on these
kernels. Check if the inet_frags 'rnd' field is present to key on
whether the upstream patch is present.  Also update Travis to the
latest 4.9 kernel release so that this patch is compile tested.

Passes Travis:
https://travis-ci.org/gvrose8192/ovs-experimental/builds/587185472

Cc: William Tu <u9012063@gmail.com>
Cc: Yi-Hung Wei <yihung.wei@gmail.com>
Cc: Yifeng Sun <pkusunyifeng@gmail.com>
Acked-by: Yi-Hung Wei <yihung.wei@gmail.com>
Signed-off-by: Greg Rose <gvrose8192@gmail.com>
Signed-off-by: Ben Pfaff <blp@ovn.org>

acinclude.m4

@@ -694,7 +694,9 @@ AC_DEFUN([OVS_CHECK_LINUX_COMPAT], [
   OVS_FIND_PARAM_IFELSE([$KSRC/include/net/protocol.h],
                         [udp_add_offload], [net],
                         [OVS_DEFINE([HAVE_UDP_ADD_OFFLOAD_TAKES_NET])])
-
+  OVS_FIND_FIELD_IFELSE([$KSRC/include/net/inet_frag.h], [inet_frags],
+                        [rnd],
+                        [OVS_DEFINE([HAVE_INET_FRAGS_RND])])
 
   if cmp -s datapath/linux/kcompat.h.new \
             datapath/linux/kcompat.h >/dev/null 2>&1; then

datapath/linux/compat/nf_conntrack_reasm.c

@@ -73,6 +73,7 @@ static inline u8 ip6_frag_ecn(const struct ipv6hdr *ipv6h)
 	return 1 << (ipv6_get_dsfield(ipv6h) & INET_ECN_MASK);
 }
 
+#ifdef HAVE_INET_FRAGS_RND
 static unsigned int nf_hash_frag(__be32 id, const struct in6_addr *saddr,
 				 const struct in6_addr *daddr)
 {
@@ -99,6 +100,7 @@ static unsigned int nf_hashfn(struct inet_frag_queue *q)
 	return nf_hash_frag(nq->id, &nq->saddr, &nq->daddr);
 }
 
+#endif /* HAVE_INET_FRAGS_RND */
 static void nf_ct_frag6_expire(unsigned long data)
 {
 	struct frag_queue *fq;
@@ -107,9 +109,14 @@ static void nf_ct_frag6_expire(unsigned long data)
 	fq = container_of((struct inet_frag_queue *)data, struct frag_queue, q);
 	net = container_of(fq->q.net, struct net, nf_frag.frags);
 
+#ifdef HAVE_INET_FRAGS_RND
 	ip6_expire_frag_queue(net, fq, &nf_frags);
+#else
+	ip6_expire_frag_queue(net, fq);
+#endif
 }
 
+#ifdef HAVE_INET_FRAGS_RND
 /* Creation primitives. */
 static inline struct frag_queue *fq_find(struct net *net, __be32 id,
 					 u32 user, struct in6_addr *src,
@@ -140,7 +147,27 @@ static inline struct frag_queue *fq_find(struct net *net, __be32 id,
 	}
 	return container_of(q, struct frag_queue, q);
 }
+#else
+static struct frag_queue *fq_find(struct net *net, __be32 id, u32 user,
+				  const struct ipv6hdr *hdr, int iif)
+{
+	struct frag_v6_compare_key key = {
+		.id = id,
+		.saddr = hdr->saddr,
+		.daddr = hdr->daddr,
+		.user = user,
+		.iif = iif,
+	};
+	struct inet_frag_queue *q;
 
+	q = inet_frag_find(&net->nf_frag.frags, &key);
+	if (!q)
+		return NULL;
+
+	return container_of(q, struct frag_queue, q);
+}
+
+#endif  /* HAVE_INET_FRAGS_RND */
 
 static int nf_ct_frag6_queue(struct frag_queue *fq, struct sk_buff *skb,
 			     const struct frag_hdr *fhdr, int nhoff)
@@ -289,7 +316,11 @@ static int nf_ct_frag6_queue(struct frag_queue *fq, struct sk_buff *skb,
 	return 0;
 
 discard_fq:
+#ifdef HAVE_INET_FRAGS_RND
 	inet_frag_kill(&fq->q, &nf_frags);
+#else
+	inet_frag_kill(&fq->q);
+#endif
 err:
 	return -1;
 }
@@ -311,7 +342,11 @@ nf_ct_frag6_reasm(struct frag_queue *fq, struct sk_buff *prev,  struct net_devic
 	int    payload_len;
 	u8 ecn;
 
+#ifdef HAVE_INET_FRAGS_RND
 	inet_frag_kill(&fq->q, &nf_frags);
+#else
+	inet_frag_kill(&fq->q);
+#endif
 
 	WARN_ON(head == NULL);
 	WARN_ON(NFCT_FRAG6_CB(head)->offset != 0);
@@ -530,8 +565,13 @@ int nf_ct_frag6_gather(struct net *net, struct sk_buff *skb, u32 user)
 	local_bh_enable();
 #endif
 
+#ifdef HAVE_INET_FRAGS_RND
 	fq = fq_find(net, fhdr->identification, user, &hdr->saddr, &hdr->daddr,
 		     ip6_frag_ecn(hdr));
+#else
+	fq = fq_find(net, fhdr->identification, user, hdr,
+		     skb->dev ? skb->dev->ifindex : 0);
+#endif
 	if (fq == NULL)
 		return -ENOMEM;
 
@@ -553,7 +593,11 @@ int nf_ct_frag6_gather(struct net *net, struct sk_buff *skb, u32 user)
 
 out_unlock:
 	spin_unlock_bh(&fq->q.lock);
+#ifdef HAVE_INET_FRAGS_RND
 	inet_frag_put(&fq->q, &nf_frags);
+#else
+	inet_frag_put(&fq->q);
+#endif
 	return ret;
 }
 
@@ -571,13 +615,17 @@ int rpl_nf_ct_frag6_init(void)
 	int ret = 0;
 
 	nf_defrag_ipv6_enable();
+#ifdef HAVE_INET_FRAGS_RND
 	nf_frags.hashfn = nf_hashfn;
+	nf_frags.match = ip6_frag_match;
+#else
+	nf_frags.rhash_params = ip6_rhash_params;
+#endif
 	nf_frags.constructor = ip6_frag_init;
 	nf_frags.destructor = NULL;
 	nf_frags.qsize = sizeof(struct frag_queue);
-	nf_frags.match = ip6_frag_match;
 	nf_frags.frag_expire = nf_ct_frag6_expire;
-#ifdef HAVE_INET_FRAGS_WITH_FRAGS_WORK
+#if defined(HAVE_INET_FRAGS_WITH_FRAGS_WORK) || !defined(HAVE_INET_FRAGS_RND)
 	nf_frags.frags_cache_name = nf_frags_cache_name;
 #endif
 #if RHEL_RELEASE_CODE < RHEL_RELEASE_VERSION(8,0)