[PATCH net v3] ipv6: omit traffic class when calculating flow hash

[Michal Kubecek]

Some of the code paths calculating flow hash for IPv6 use flowlabel member
of struct flowi6 which, despite its name, encodes both flow label and
traffic class. If traffic class changes within a TCP connection (as e.g.
ssh does), ECMP route can switch between path. It's also inconsistent with
other code paths where ip6_flowlabel() (returning only flow label) is used
to feed the key.

Use only flow label everywhere, including one place where hash key is set
using ip6_flowinfo().

Fixes: 51ebd3181572 ("ipv6: add support of equal cost multipath (ECMP)")
Fixes: f70ea018da06 ("net: Add functions to get skb->hash based on flow structures")
Signed-off-by: Michal Kubecek <mkubecek@xxxxxxx>
---
v2: introduce and use an inline helper as suggested by David Ahern
v3: keep the cast out of the helper to make future cleanup easier

 include/net/ipv6.h        | 5 +++++
 net/core/flow_dissector.c | 2 +-
 net/ipv6/route.c          | 4 ++--
 3 files changed, 8 insertions(+), 3 deletions(-)

diff --git a/include/net/ipv6.h b/include/net/ipv6.h
index 836f31af1369..a406f2e8680a 100644
--- a/include/net/ipv6.h
+++ b/include/net/ipv6.h
@@ -906,6 +906,11 @@ static inline __be32 ip6_make_flowinfo(unsigned int tclass, __be32 flowlabel)
 	return htonl(tclass << IPV6_TCLASS_SHIFT) | flowlabel;
 }
 
+static inline __be32 flowi6_get_flowlabel(const struct flowi6 *fl6)
+{
+	return fl6->flowlabel & IPV6_FLOWLABEL_MASK;
+}
+
 /*
  *	Prototypes exported by ipv6
  */
diff --git a/net/core/flow_dissector.c b/net/core/flow_dissector.c
index d29f09bc5ff9..0234f8d1f0ac 100644
--- a/net/core/flow_dissector.c
+++ b/net/core/flow_dissector.c
@@ -1334,7 +1334,7 @@ __u32 __get_hash_from_flowi6(const struct flowi6 *fl6, struct flow_keys *keys)
 	keys->ports.src = fl6->fl6_sport;
 	keys->ports.dst = fl6->fl6_dport;
 	keys->keyid.keyid = fl6->fl6_gre_key;
-	keys->tags.flow_label = (__force u32)fl6->flowlabel;
+	keys->tags.flow_label = (__force u32)flowi6_get_flowlabel(fl6);
 	keys->basic.ip_proto = fl6->flowi6_proto;
 
 	return flow_hash_from_keys(keys);
diff --git a/net/ipv6/route.c b/net/ipv6/route.c
index f4d61736c41a..4530a82aaa2e 100644
--- a/net/ipv6/route.c
+++ b/net/ipv6/route.c
@@ -1868,7 +1868,7 @@ static void ip6_multipath_l3_keys(const struct sk_buff *skb,
 	} else {
 		keys->addrs.v6addrs.src = key_iph->saddr;
 		keys->addrs.v6addrs.dst = key_iph->daddr;
-		keys->tags.flow_label = ip6_flowinfo(key_iph);
+		keys->tags.flow_label = ip6_flowlabel(key_iph);
 		keys->basic.ip_proto = key_iph->nexthdr;
 	}
 }
@@ -1889,7 +1889,7 @@ u32 rt6_multipath_hash(const struct net *net, const struct flowi6 *fl6,
 		} else {
 			hash_keys.addrs.v6addrs.src = fl6->saddr;
 			hash_keys.addrs.v6addrs.dst = fl6->daddr;
-			hash_keys.tags.flow_label = (__force u32)fl6->flowlabel;
+			hash_keys.tags.flow_label = (__force u32)flowi6_get_flowlabel(fl6);
 			hash_keys.basic.ip_proto = fl6->flowi6_proto;
 		}
 		break;
-- 
2.17.1