Hi Florian, On Sat, 4 Nov 2023, Florian Westphal wrote: > Jozsef Kadlecsik <kadlec@xxxxxxxxxxxxx> wrote: > > Linkui Xiao reported that there's a race condition when ipset swap and destroy is > > called, which can lead to crash in add/del/test element operations. Swap then > > destroy are usual operations to replace a set with another one in a production > > system. The issue can in some cases be reproduced with the script: > > > iptables -A INPUT -m set --match-set hash_ip1 src -j ACCEPT > > while [ 1 ] > > do > > # ... Ongoing traffic... > > ipset create hash_ip2 hash:net family inet hashsize 1024 maxelem 1048576 > > ipset add hash_ip2 172.20.0.0/16 > > ipset swap hash_ip1 hash_ip2 > > ipset destroy hash_ip2 > > sleep 0.05 > > done > > > > In the race case the possible order of the operations are > > > > CPU0 CPU1 > > ip_set_test > > ipset swap hash_ip1 hash_ip2 > > ipset destroy hash_ip2 > > hash_net_kadt > > > > Swap replaces hash_ip1 with hash_ip2 and then destroy removes hash_ip2 which > > is the original hash_ip1. ip_set_test was called on hash_ip1 and because destroy > > removed it, hash_net_kadt crashes. > > > > The fix is to protect both the list of the sets and the set pointers in an extended RCU > > region and before exiting ip_set_swap(), wait to finish all started rcu_read_lock(). > > The first version of the patch was written by Linkui Xiao <xiaolinkui@xxxxxxxxxx>. > > > > v2: synchronize_rcu() is moved into ip_set_swap() in order not to burden > > ip_set_destroy() unnecessarily when all sets are destroyed. > > Hmm. Isn't it enough to only call synchronize_rcu() in ip_set_swap? > > All netfilter hooks run with rcu_read_lock() held, em_ipset.c wraps the > entire ip_set_test() in rcu read lock/unlock pair. Hm, actually, you are right. Technically there's no need to extend the rcu_read_lock() protected area inside ipset itself. > > @@ -704,13 +704,18 @@ ip_set_rcu_get(struct net *net, ip_set_id_t index) > > struct ip_set_net *inst = ip_set_pernet(net); > > > > rcu_read_lock(); > > - /* ip_set_list itself needs to be protected */ > > + /* ip_set_list and the set pointer need to be protected */ > > set = rcu_dereference(inst->ip_set_list)[index]; > > - rcu_read_unlock(); > > > > return set; > > } > > ... so I don't understand why ip_set_rcu_get() has to extend > the locked section. > > AFAICS there are only two type of callers: > 1. rcu read lock is already held (datapath) > 2. ipset nfnl subsys mutex is held > > *probably* This could be changed in a separate patch to: > > - rcu_read_lock(); > - /* ip_set_list itself needs to be protected */ > - set = rcu_dereference(inst->ip_set_list)[index]; > - rcu_read_unlock(); > + /* ip_set_list and the set pointer need to be protected */ > + return rcu_dereference_check(inst->ip_set_list, lockdep_nfnl_is_held(NFNL_SUBSYS_IPSET)[index]; > > This is an example, probably better to add a small > "ip_set_dereference_nfnl" helper to hide the lockdep construct... > > Not saying the patch is wrong; rcu read locks nest and > ipset locking is not simple so I might be missing something. I'm going to rework the patch, thanks for your input! Best regards, Jozsef -- E-mail : kadlec@xxxxxxxxxxxxxxxxx, kadlecsik.jozsef@xxxxxxxxx PGP key : https://wigner.hu/~kadlec/pgp_public_key.txt Address : Wigner Research Centre for Physics H-1525 Budapest 114, POB. 49, Hungary
