AZL-50716

In the Linux kernel, the following vulnerability has been resolved:

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 (icmpglobalallow())

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) icmpglobalallow() 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) icmpglobalconsume() 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.