On Thu, 4 Jul 2024 12:54:18 +0200 Florian Westphal <fw@xxxxxxxxx> > Hillf Danton <hdanton@xxxxxxxx> wrote: > > On Wed, 3 Jul 2024 15:01:07 +0200 Florian Westphal <fw@xxxxxxxxx> > > > Hillf Danton <hdanton@xxxxxxxx> wrote: > > > > On Wed, 3 Jul 2024 12:52:15 +0200 Florian Westphal <fw@xxxxxxxxx> > > > > > Hillf Danton <hdanton@xxxxxxxx> wrote: > > > > > > Given trans->table goes thru the lifespan of trans, your proposal is a bandaid > > > > > > if trans outlives table. > > > > > > > > > > trans must never outlive table. > > > > > > > > > What is preventing trans from being freed after closing sock, given > > > > trans is freed in workqueue? > > > > > > > > close sock > > > > queue work > > > > > > The notifier acquires the transaction mutex, locking out all other > > > transactions, so no further transactions requests referencing > > > the table can be queued. > > > > > As per the syzbot report, trans->table could be instantiated before > > notifier acquires the transaction mutex. And in fact the lock helps > > trans outlive table even with your patch. > > > > cpu1 cpu2 > > --- --- > > transB->table = A > > lock trans mutex > > flush work > > free A > > unlock trans mutex > > > > queue work to free transB > > Can you show a crash reproducer or explain how this assign > and queueing happens unordered wrt. cpu2? > Not so difficult. > This should look like this: > > cpu1 cpu2 > --- --- > lock trans mutex > lock trans mutex -> blocks > transB->table = A > queue work to free transB > unlock trans mutex > lock trans mutex returns > flush work > free A > unlock trans mutex > If your patch is correct, it should survive a warning. #syz test https://git.kernel.org/pub/scm/linux/kernel/git/netdev/net-next.git 1c5fc27bc48a --- x/net/netfilter/nf_tables_api.c +++ y/net/netfilter/nf_tables_api.c @@ -11552,9 +11552,10 @@ static int nft_rcv_nl_event(struct notif gc_seq = nft_gc_seq_begin(nft_net); - if (!list_empty(&nf_tables_destroy_list)) - nf_tables_trans_destroy_flush_work(); + nf_tables_trans_destroy_flush_work(); again: + WARN_ON(!list_empty(&nft_net->commit_list)); + list_for_each_entry(table, &nft_net->tables, list) { if (nft_table_has_owner(table) && n->portid == table->nlpid) { --
