[PATCH v2 net-next 3/9] ipv6: snmp: do not track per idev ICMP6_MIB_RATELIMITHOST

[Eric Dumazet <edumazet@google.com>]

Blamed commit added a critical false sharing on a single
atomic_long_t under DOS, like receiving UDP packets
to closed ports.

Per netns ICMP6_MIB_RATELIMITHOST tracking uses per-cpu
storage and is enough, we do not need per-device and slow tracking.

Fixes: d0941130c9351 ("icmp: Add counters for rate limits")
Signed-off-by: Eric Dumazet <edumazet@google.com>
Cc: Jamie Bainbridge <jamie.bainbridge@gmail.com>
Cc: Abhishek Rawal <rawal.abhishek92@gmail.com>
---
 net/ipv6/icmp.c | 3 +--
 net/ipv6/proc.c | 6 +++++-
 2 files changed, 6 insertions(+), 3 deletions(-)

diff --git a/net/ipv6/icmp.c b/net/ipv6/icmp.c
index 95cdd4cacb00..56c974cf75d1 100644
--- a/net/ipv6/icmp.c
+++ b/net/ipv6/icmp.c
@@ -230,8 +230,7 @@ static bool icmpv6_xrlim_allow(struct sock *sk, u8 type,
 	}
 	rcu_read_unlock();
 	if (!res)
-		__ICMP6_INC_STATS(net, ip6_dst_idev(dst),
-				  ICMP6_MIB_RATELIMITHOST);
+		__ICMP6_INC_STATS(net, NULL, ICMP6_MIB_RATELIMITHOST);
 	else
 		icmp_global_consume(net);
 	dst_release(dst);
diff --git a/net/ipv6/proc.c b/net/ipv6/proc.c
index 92ed04729c2f..73296f38c252 100644
--- a/net/ipv6/proc.c
+++ b/net/ipv6/proc.c
@@ -94,6 +94,7 @@ static const struct snmp_mib snmp6_icmp6_list[] = {
 	SNMP_MIB_ITEM("Icmp6OutMsgs", ICMP6_MIB_OUTMSGS),
 	SNMP_MIB_ITEM("Icmp6OutErrors", ICMP6_MIB_OUTERRORS),
 	SNMP_MIB_ITEM("Icmp6InCsumErrors", ICMP6_MIB_CSUMERRORS),
+/* ICMP6_MIB_RATELIMITHOST needs to be last, see snmp6_dev_seq_show(). */
 	SNMP_MIB_ITEM("Icmp6OutRateLimitHost", ICMP6_MIB_RATELIMITHOST),
 };
 
@@ -242,8 +243,11 @@ static int snmp6_dev_seq_show(struct seq_file *seq, void *v)
 			      snmp6_ipstats_list,
 			      ARRAY_SIZE(snmp6_ipstats_list),
 			      offsetof(struct ipstats_mib, syncp));
+
+	/* Per idev icmp stats do not have ICMP6_MIB_RATELIMITHOST */
 	snmp6_seq_show_item(seq, NULL, idev->stats.icmpv6dev->mibs,
-			    snmp6_icmp6_list, ARRAY_SIZE(snmp6_icmp6_list));
+			    snmp6_icmp6_list, ARRAY_SIZE(snmp6_icmp6_list) - 1);
+
 	snmp6_seq_show_icmpv6msg(seq, idev->stats.icmpv6msgdev->mibs);
 	return 0;
 }
-- 
2.51.0.355.g5224444f11-goog