Subject: [PATCH v6 net-next 2/3] net/ipv6: multipath routing: configurable seed

From: Pavel Balaev <[email-masked]>
Date: Wed, 28 Apr 2021 15:33:57 +0300

Ability for a user to assign seed value to IPv6 multipath route hashes.
This patch adds sysctl variable: net.ipv6.fib_multipath_hash_seed.

Signed-off-by: Pavel Balaev <[email-masked]>
---
 include/net/netns/ipv6.h   |  3 ++
 net/ipv6/route.c           | 10 +++-
 net/ipv6/sysctl_net_ipv6.c | 96 ++++++++++++++++++++++++++++++++++++++
 3 files changed, 108 insertions(+), 1 deletion(-)

diff --git a/include/net/netns/ipv6.h b/include/net/netns/ipv6.h
index 808f0f79e..6bb383b0a 100644
--- a/include/net/netns/ipv6.h
+++ b/include/net/netns/ipv6.h
@@ -8,6 +8,7 @@
 #ifndef __NETNS_IPV6_H__
 #define __NETNS_IPV6_H__
 #include <net/dst_ops.h>
+#include <linux/siphash.h>
 #include <uapi/linux/icmpv6.h>
 
 struct ctl_table_header;
@@ -30,6 +31,7 @@ struct netns_sysctl_ipv6 {
 	int ip6_rt_min_advmss;
 	u8 bindv6only;
 	u8 multipath_hash_policy;
+	u8 multipath_hash_seed;
 	u8 flowlabel_consistency;
 	u8 auto_flowlabels;
 	int icmpv6_time;
@@ -107,6 +109,7 @@ struct netns_ipv6 {
 	struct fib_rules_ops	*mr6_rules_ops;
 #endif
 #endif
+	siphash_key_t __rcu	*multipath_hash_seed_ctx;
 	atomic_t		dev_addr_genid;
 	atomic_t		fib6_sernum;
 	struct seg6_pernet_data *seg6_data;
diff --git a/net/ipv6/route.c b/net/ipv6/route.c
index 28801ae80..70c488812 100644
--- a/net/ipv6/route.c
+++ b/net/ipv6/route.c
@@ -2331,6 +2331,7 @@ u32 rt6_multipath_hash(const struct net *net, const struct flowi6 *fl6,
 		       const struct sk_buff *skb, struct flow_keys *flkeys)
 {
 	struct flow_keys hash_keys;
+	siphash_key_t *seed_ctx;
 	u32 mhash;
 
 	switch (ip6_multipath_hash_policy(net)) {
@@ -2414,7 +2415,14 @@ u32 rt6_multipath_hash(const struct net *net, const struct flowi6 *fl6,
 		}
 		break;
 	}
-	mhash = flow_hash_from_keys(&hash_keys);
+
+	rcu_read_lock();
+	seed_ctx = rcu_dereference(net->ipv6.multipath_hash_seed_ctx);
+	if (seed_ctx)
+		mhash = flow_multipath_hash_from_keys(&hash_keys, seed_ctx);
+	else
+		mhash = flow_hash_from_keys(&hash_keys);
+	rcu_read_unlock();
 
 	return mhash >> 1;
 }
diff --git a/net/ipv6/sysctl_net_ipv6.c b/net/ipv6/sysctl_net_ipv6.c
index 27102c3d6..349251cb7 100644
--- a/net/ipv6/sysctl_net_ipv6.c
+++ b/net/ipv6/sysctl_net_ipv6.c
@@ -40,6 +40,94 @@ static int proc_rt6_multipath_hash_policy(struct ctl_table *table, int write,
 	return ret;
 }
 
+#define RT6_MULTIPATH_SEED_KEY_LENGTH sizeof(siphash_key_t)
+#define RT6_MULTIPATH_SEED_RANDOM "random"
+static int proc_rt6_multipath_hash_seed(struct ctl_table *table, int write,
+					void *buffer, size_t *lenp, loff_t *ppos)
+{
+	struct net *net = container_of(table->data, struct net,
+	    ipv6.sysctl.multipath_hash_seed);
+	/* maxlen to print the keys in hex (*2) and a comma in between keys. */
+	struct ctl_table tbl = {
+		.maxlen = ((RT6_MULTIPATH_SEED_KEY_LENGTH * 2) + 2)
+	};
+	siphash_key_t user_key, *ctx;
+	__le64 key[2];
+	int ret;
+
+	tbl.data = kmalloc(tbl.maxlen, GFP_KERNEL);
+
+	if (!tbl.data)
+		return -ENOMEM;
+
+	rcu_read_lock();
+	ctx = rcu_dereference(net->ipv6.multipath_hash_seed_ctx);
+	if (ctx) {
+		put_unaligned_le64(ctx->key[0], &key[0]);
+		put_unaligned_le64(ctx->key[1], &key[1]);
+		user_key.key[0] = le64_to_cpu(key[0]);
+		user_key.key[1] = le64_to_cpu(key[1]);
+
+		snprintf(tbl.data, tbl.maxlen, "%016llx,%016llx",
+			 user_key.key[0], user_key.key[1]);
+	} else {
+		snprintf(tbl.data, tbl.maxlen, "%s", RT6_MULTIPATH_SEED_RANDOM);
+	}
+	rcu_read_unlock();
+
+	ret = proc_dostring(&tbl, write, buffer, lenp, ppos);
+
+	if (write && ret == 0) {
+		siphash_key_t *new_ctx, *old_ctx;
+
+		if (!strcmp(tbl.data, RT6_MULTIPATH_SEED_RANDOM)) {
+			rtnl_lock();
+			old_ctx = rtnl_dereference(net->ipv6.multipath_hash_seed_ctx);
+			RCU_INIT_POINTER(net->ipv6.multipath_hash_seed_ctx, NULL);
+			rtnl_unlock();
+			if (old_ctx) {
+				synchronize_net();
+				kfree_sensitive(old_ctx);
+			}
+
+			pr_debug("multipath hash seed set to random value\n");
+			goto out;
+		}
+
+		if (sscanf(tbl.data, "%llx,%llx", user_key.key, user_key.key + 1) != 2) {
+			ret = -EINVAL;
+			goto out;
+		}
+
+		key[0] = cpu_to_le64(user_key.key[0]);
+		key[1] = cpu_to_le64(user_key.key[1]);
+		pr_debug("multipath hash seed set to 0x%llx,0x%llx\n",
+			 user_key.key[0], user_key.key[1]);
+
+		new_ctx = kmalloc(sizeof(*new_ctx), GFP_KERNEL);
+		if (!new_ctx) {
+			ret = -ENOMEM;
+			goto out;
+		}
+
+		new_ctx->key[0] = get_unaligned_le64(&key[0]);
+		new_ctx->key[1] = get_unaligned_le64(&key[1]);
+
+		rtnl_lock();
+		old_ctx = rtnl_dereference(net->ipv6.multipath_hash_seed_ctx);
+		rcu_assign_pointer(net->ipv6.multipath_hash_seed_ctx, new_ctx);
+		rtnl_unlock();
+		if (old_ctx) {
+			synchronize_net();
+			kfree_sensitive(old_ctx);
+		}
+	}
+
+out:
+	kfree(tbl.data);
+	return ret;
+}
+
 static struct ctl_table ipv6_table_template[] = {
 	{
 		.procname	= "bindv6only",
@@ -151,6 +239,14 @@ static struct ctl_table ipv6_table_template[] = {
 		.extra1		= SYSCTL_ZERO,
 		.extra2		= &two,
 	},
+	{
+		.procname	= "fib_multipath_hash_seed",
+		.data		= &init_net.ipv6.sysctl.multipath_hash_seed,
+		/* maxlen to print the keys in hex (*2) and a comma in between keys. */
+		.maxlen		= (RT6_MULTIPATH_SEED_KEY_LENGTH * 2) + 2,
+		.mode		= 0600,
+		.proc_handler	= proc_rt6_multipath_hash_seed,
+	},
 	{
 		.procname	= "seg6_flowlabel",
 		.data		= &init_net.ipv6.sysctl.seg6_flowlabel,
-- 
2.31.1