ipv6: Add a sysctl to control multipath hash fields

A subsequent patch will add a new multipath hash policy where the packet
fields used for multipath hash calculation are determined by user space.
This patch adds a sysctl that allows user space to set these fields.

The packet fields are represented using a bitmask and are common between
IPv4 and IPv6 to allow user space to use the same numbering across both
protocols. For example, to hash based on standard 5-tuple:

 # sysctl -w net.ipv6.fib_multipath_hash_fields=0x0037
 net.ipv6.fib_multipath_hash_fields = 0x0037

To avoid introducing holes in 'struct netns_sysctl_ipv6', move the
'bindv6only' field after the multipath hash fields.

The kernel rejects unknown fields, for example:

 # sysctl -w net.ipv6.fib_multipath_hash_fields=0x1000
 sysctl: setting key "net.ipv6.fib_multipath_hash_fields": Invalid argument

Signed-off-by: Ido Schimmel <idosch@nvidia.com>
Reviewed-by: David Ahern <dsahern@kernel.org>
Signed-off-by: David S. Miller <davem@davemloft.net>

Documentation/networking/ip-sysctl.rst

@@ -1773,6 +1773,33 @@ fib_multipath_hash_policy - INTEGER
 	- 1 - Layer 4 (standard 5-tuple)
 	- 2 - Layer 3 or inner Layer 3 if present
 
+fib_multipath_hash_fields - UNSIGNED INTEGER
+	When fib_multipath_hash_policy is set to 3 (custom multipath hash), the
+	fields used for multipath hash calculation are determined by this
+	sysctl.
+
+	This value is a bitmask which enables various fields for multipath hash
+	calculation.
+
+	Possible fields are:
+
+	====== ============================
+	0x0001 Source IP address
+	0x0002 Destination IP address
+	0x0004 IP protocol
+	0x0008 Flow Label
+	0x0010 Source port
+	0x0020 Destination port
+	0x0040 Inner source IP address
+	0x0080 Inner destination IP address
+	0x0100 Inner IP protocol
+	0x0200 Inner Flow Label
+	0x0400 Inner source port
+	0x0800 Inner destination port
+	====== ============================
+
+	Default: 0x0007 (source IP, destination IP and IP protocol)
+
 anycast_src_echo_reply - BOOLEAN
 	Controls the use of anycast addresses as source addresses for ICMPv6
 	echo reply

include/net/ipv6.h

@@ -926,11 +926,19 @@ static inline int ip6_multipath_hash_policy(const struct net *net)
 {
 	return net->ipv6.sysctl.multipath_hash_policy;
 }
+static inline u32 ip6_multipath_hash_fields(const struct net *net)
+{
+	return net->ipv6.sysctl.multipath_hash_fields;
+}
 #else
 static inline int ip6_multipath_hash_policy(const struct net *net)
 {
 	return 0;
 }
+static inline u32 ip6_multipath_hash_fields(const struct net *net)
+{
+	return 0;
+}
 #endif
 
 /*

include/net/netns/ipv6.h

@@ -28,8 +28,9 @@ struct netns_sysctl_ipv6 {
 	int ip6_rt_gc_elasticity;
 	int ip6_rt_mtu_expires;
 	int ip6_rt_min_advmss;
-	u8 bindv6only;
+	u32 multipath_hash_fields;
 	u8 multipath_hash_policy;
+	u8 bindv6only;
 	u8 flowlabel_consistency;
 	u8 auto_flowlabels;
 	int icmpv6_time;

net/ipv6/ip6_fib.c

@@ -32,6 +32,7 @@
 #include <net/lwtunnel.h>
 #include <net/fib_notifier.h>
 
+#include <net/ip_fib.h>
 #include <net/ip6_fib.h>
 #include <net/ip6_route.h>
 
@@ -2355,6 +2356,10 @@ static int __net_init fib6_net_init(struct net *net)
 	if (err)
 		return err;
 
+	/* Default to 3-tuple */
+	net->ipv6.sysctl.multipath_hash_fields =
+		FIB_MULTIPATH_HASH_FIELD_DEFAULT_MASK;
+
 	spin_lock_init(&net->ipv6.fib6_gc_lock);
 	rwlock_init(&net->ipv6.fib6_walker_lock);
 	INIT_LIST_HEAD(&net->ipv6.fib6_walkers);

net/ipv6/sysctl_net_ipv6.c

@@ -17,6 +17,7 @@
 #include <net/addrconf.h>
 #include <net/inet_frag.h>
 #include <net/netevent.h>
+#include <net/ip_fib.h>
 #ifdef CONFIG_NETLABEL
 #include <net/calipso.h>
 #endif
@@ -24,6 +25,8 @@
 static int two = 2;
 static int flowlabel_reflect_max = 0x7;
 static int auto_flowlabels_max = IP6_AUTO_FLOW_LABEL_MAX;
+static u32 rt6_multipath_hash_fields_all_mask =
+	FIB_MULTIPATH_HASH_FIELD_ALL_MASK;
 
 static int proc_rt6_multipath_hash_policy(struct ctl_table *table, int write,
 					  void *buffer, size_t *lenp, loff_t *ppos)
@@ -151,6 +154,15 @@ static struct ctl_table ipv6_table_template[] = {
 		.extra1		= SYSCTL_ZERO,
 		.extra2		= &two,
 	},
+	{
+		.procname	= "fib_multipath_hash_fields",
+		.data		= &init_net.ipv6.sysctl.multipath_hash_fields,
+		.maxlen		= sizeof(u32),
+		.mode		= 0644,
+		.proc_handler	= proc_douintvec_minmax,
+		.extra1		= SYSCTL_ONE,
+		.extra2		= &rt6_multipath_hash_fields_all_mask,
+	},
 	{
 		.procname	= "seg6_flowlabel",
 		.data		= &init_net.ipv6.sysctl.seg6_flowlabel,