xiaolinkui <xiaolinkui@xxxxxxx> wrote: > From: Linkui Xiao <xiaolinkui@xxxxxxxxxx> > > Before destroying the ipset, take a check on sequence to ensure that the > ip_set_test operation of this ipset has been completed. > > The code of set_match_v4 is protected by addend=xt_write_recseq_begin() and > xt_write_recseq_end(addend). So we can ensure that the test operation is > completed by reading seqcount. Nope, please don't do this, the xt_set can also be used from nft_compat which doesn't use the xtables packet traversers. I'd rather use synchonize_rcu() once in ip_set_destroy(), that will make sure all concurrent traversers are gone. That said, I still do not understand this fix, the match / target destroy hooks are called after the table has been completely replaced, i.e., while packets can still be in flight no packets should be within the ipset lookup functions when this happens, and no more packets should be able to enter them. AFAICS the request to delete the set will fail if its still referenced via any rule. xt_set holds references to the sets. So: 1. set have dropped all references 2. userspace *can* delete the set 3. we get crash because xt_set was still within a sets eval function. I don't see how 3) can happen, xt table replace isn't supposed to call the xt_set destroy functions until after table replace. We even release the entire x_table blob right afterwards.
