[PATCH net] 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 incosistent 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>
---
 net/core/flow_dissector.c | 3 ++-
 net/ipv6/route.c          | 5 +++--
 2 files changed, 5 insertions(+), 3 deletions(-)

diff --git a/net/core/flow_dissector.c b/net/core/flow_dissector.c
index d29f09bc5ff9..441d3db76e8e 100644
--- a/net/core/flow_dissector.c
+++ b/net/core/flow_dissector.c
@@ -1334,7 +1334,8 @@ __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)(fl6->flowlabel &
+					      IPV6_FLOWLABEL_MASK);
 	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..fcbacf1677f8 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 +1889,8 @@ 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)(fl6->flowlabel &
+								  IPV6_FLOWLABEL_MASK);
 			hash_keys.basic.ip_proto = fl6->flowi6_proto;
 		}
 		break;
-- 
2.17.1