icmp: change the order of rate limits

ICMP messages are ratelimited :

After the blamed commits, the two rate limiters are applied in this order:

1) host wide ratelimit (icmp_global_allow())

2) Per destination ratelimit (inetpeer based)

In order to avoid side-channels attacks, we need to apply
the per destination check first.

This patch makes the following change :

1) icmp_global_allow() checks if the host wide limit is reached.
   But credits are not yet consumed. This is deferred to 3)

2) The per destination limit is checked/updated.
   This might add a new node in inetpeer tree.

3) icmp_global_consume() consumes tokens if prior operations succeeded.

This means that host wide ratelimit is still effective
in keeping inetpeer tree small even under DDOS.

As a bonus, I removed icmp_global.lock as the fast path
can use a lock-free operation.

Fixes: c0303efeab73 ("net: reduce cycles spend on ICMP replies that gets rate limited")
Fixes: 4cdf507d5452 ("icmp: add a global rate limitation")
Reported-by: Keyu Man <keyu.man@email.ucr.edu>
Signed-off-by: Eric Dumazet <edumazet@google.com>
Reviewed-by: David Ahern <dsahern@kernel.org>
Cc: Jesper Dangaard Brouer <hawk@kernel.org>
Cc: stable@vger.kernel.org
Link: https://patch.msgid.link/20240829144641.3880376-2-edumazet@google.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

1 files changed, 18 insertions, 10 deletions

diff --git a/net/ipv6/icmp.c b/net/ipv6/icmp.c
index 7b31674644ef..46f70e4a8351 100644
--- a/net/ipv6/icmp.c
+++ b/net/ipv6/icmp.c
@@ -175,14 +175,16 @@ static bool icmpv6_mask_allow(struct net *net, int type)
 	return false;
 }
 
-static bool icmpv6_global_allow(struct net *net, int type)
+static bool icmpv6_global_allow(struct net *net, int type,
+				bool *apply_ratelimit)
 {
 	if (icmpv6_mask_allow(net, type))
 		return true;
 
-	if (icmp_global_allow())
+	if (icmp_global_allow()) {
+		*apply_ratelimit = true;
 		return true;
-
+	}
 	__ICMP_INC_STATS(net, ICMP_MIB_RATELIMITGLOBAL);
 	return false;
 }
@@ -191,13 +193,13 @@ static bool icmpv6_global_allow(struct net *net, int type)
  * Check the ICMP output rate limit
  */
 static bool icmpv6_xrlim_allow(struct sock *sk, u8 type,
-			       struct flowi6 *fl6)
+			       struct flowi6 *fl6, bool apply_ratelimit)
 {
 	struct net *net = sock_net(sk);
 	struct dst_entry *dst;
 	bool res = false;
 
-	if (icmpv6_mask_allow(net, type))
+	if (!apply_ratelimit)
 		return true;
 
 	/*
@@ -228,6 +230,8 @@ static bool icmpv6_xrlim_allow(struct sock *sk, u8 type,
 	if (!res)
 		__ICMP6_INC_STATS(net, ip6_dst_idev(dst),
 				  ICMP6_MIB_RATELIMITHOST);
+	else
+		icmp_global_consume();
 	dst_release(dst);
 	return res;
 }
@@ -452,6 +456,7 @@ void icmp6_send(struct sk_buff *skb, u8 type, u8 code, __u32 info,
 	struct net *net;
 	struct ipv6_pinfo *np;
 	const struct in6_addr *saddr = NULL;
+	bool apply_ratelimit = false;
 	struct dst_entry *dst;
 	struct icmp6hdr tmp_hdr;
 	struct flowi6 fl6;
@@ -533,11 +538,12 @@ void icmp6_send(struct sk_buff *skb, u8 type, u8 code, __u32 info,
 		return;
 	}
 
-	/* Needed by both icmp_global_allow and icmpv6_xmit_lock */
+	/* Needed by both icmpv6_global_allow and icmpv6_xmit_lock */
 	local_bh_disable();
 
 	/* Check global sysctl_icmp_msgs_per_sec ratelimit */
-	if (!(skb->dev->flags & IFF_LOOPBACK) && !icmpv6_global_allow(net, type))
+	if (!(skb->dev->flags & IFF_LOOPBACK) &&
+	    !icmpv6_global_allow(net, type, &apply_ratelimit))
 		goto out_bh_enable;
 
 	mip6_addr_swap(skb, parm);
@@ -575,7 +581,7 @@ void icmp6_send(struct sk_buff *skb, u8 type, u8 code, __u32 info,
 
 	np = inet6_sk(sk);
 
-	if (!icmpv6_xrlim_allow(sk, type, &fl6))
+	if (!icmpv6_xrlim_allow(sk, type, &fl6, apply_ratelimit))
 		goto out;
 
 	tmp_hdr.icmp6_type = type;
@@ -717,6 +723,7 @@ static enum skb_drop_reason icmpv6_echo_reply(struct sk_buff *skb)
 	struct ipv6_pinfo *np;
 	const struct in6_addr *saddr = NULL;
 	struct icmp6hdr *icmph = icmp6_hdr(skb);
+	bool apply_ratelimit = false;
 	struct icmp6hdr tmp_hdr;
 	struct flowi6 fl6;
 	struct icmpv6_msg msg;
@@ -781,8 +788,9 @@ static enum skb_drop_reason icmpv6_echo_reply(struct sk_buff *skb)
 		goto out;
 
 	/* Check the ratelimit */
-	if ((!(skb->dev->flags & IFF_LOOPBACK) && !icmpv6_global_allow(net, ICMPV6_ECHO_REPLY)) ||
-	    !icmpv6_xrlim_allow(sk, ICMPV6_ECHO_REPLY, &fl6))
+	if ((!(skb->dev->flags & IFF_LOOPBACK) &&
+	    !icmpv6_global_allow(net, ICMPV6_ECHO_REPLY, &apply_ratelimit)) ||
+	    !icmpv6_xrlim_allow(sk, ICMPV6_ECHO_REPLY, &fl6, apply_ratelimit))
 		goto out_dst_release;
 
 	idev = __in6_dev_get(skb->dev);