netfilter: ipset: fix performance regression in swap operation

Vulnerability Description

In the Linux kernel, the following vulnerability has been resolved: netfilter: ipset: fix performance regression in swap operation The patch "netfilter: ipset: fix race condition between swap/destroy and kernel side add/del/test", commit 28628fa9 fixes a race condition. But the synchronize_rcu() added to the swap function unnecessarily slows it down: it can safely be moved to destroy and use call_rcu() instead. Eric Dumazet pointed out that simply calling the destroy functions as rcu callback does not work: sets with timeout use garbage collectors which need cancelling at destroy which can wait. Therefore the destroy functions are split into two: cancelling garbage collectors safely at executing the command received by netlink and moving the remaining part only into the rcu callback.

References

• https://git.kernel.org/stable/c/c7f2733e5011bfd136f1ca93497394d43aa76225
• https://git.kernel.org/stable/c/a24d5f2ac8ef702a58e55ec276aad29b4bd97e05
• https://git.kernel.org/stable/c/c2dc077d8f722a1c73a24e674f925602ee5ece49
• https://git.kernel.org/stable/c/653bc5e6d9995d7d5f497c665b321875a626161c
• https://git.kernel.org/stable/c/b93a6756a01f4fd2f329a39216f9824c56a66397
• https://git.kernel.org/stable/c/970709a67696b100a57b33af1a3d75fc34b747eb
• https://git.kernel.org/stable/c/97f7cf1cd80eeed3b7c808b7c12463295c751001