icmp: prevent possible overflow in icmp_global_allow()

Following expression can overflow
if sysctl_icmp_msgs_per_sec is big enough.

sysctl_icmp_msgs_per_sec * delta / HZ;

Fixes: 4cdf507 ("icmp: add a global rate limitation")
Signed-off-by: Eric Dumazet <edumazet@google.com>
Reviewed-by: Kuniyuki Iwashima <kuniyu@google.com>
Link: https://patch.msgid.link/20260216142832.3834174-2-edumazet@google.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

Author: edumazet

net/ipv4/icmp.c

@@ -250,7 +250,8 @@ bool icmp_global_allow(struct net *net)
 	if (delta < HZ / 50)
 		return false;
 
-	incr = READ_ONCE(net->ipv4.sysctl_icmp_msgs_per_sec) * delta / HZ;
+	incr = READ_ONCE(net->ipv4.sysctl_icmp_msgs_per_sec);
+	incr = div_u64((u64)incr * delta, HZ);
 	if (!incr)
 		return false;