icmp: change the order of rate limits

Vulnerability Description

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 (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.

References

• https://git.kernel.org/stable/c/997ba8889611891f91e8ad83583466aeab6239a3
• https://git.kernel.org/stable/c/662ec52260cc07b9ae53ecd3925183c29d34288b
• https://git.kernel.org/stable/c/a7722921adb046e3836eb84372241f32584bdb07
• https://git.kernel.org/stable/c/483397b4ba280813e4a9c161a0a85172ddb43d19
• https://git.kernel.org/stable/c/8c2bd38b95f75f3d2a08c93e35303e26d480d24e