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Quoting Daniel Borkmann: "When adding connection tracking template rules to a netns, f.e. to configure netfilter zones, the kernel will endlessly busy-loop as soon as we try to delete the given netns in case there's at least one template present, which is problematic i.e. if there is such bravery that the priviledged user inside the netns is assumed untrusted. Minimal example: ip netns add foo ip netns exec foo iptables -t raw -A PREROUTING -d 1.2.3.4 -j CT --zone 1 ip netns del foo What happens is that when nf_ct_iterate_cleanup() is being called from nf_conntrack_cleanup_net_list() for a provided netns, we always end up with a net->ct.count > 0 and thus jump back to i_see_dead_people. We don't get a soft-lockup as we still have a schedule() point, but the serving CPU spins on 100% from that point onwards. Since templates are normally allocated with nf_conntrack_alloc(), we also bump net->ct.count. The issue why they are not yet nf_ct_put() is because the per netns .exit() handler from x_tables (which would eventually invoke xt_CT's xt_ct_tg_destroy() that drops reference on info->ct) is called in the dependency chain at a *later* point in time than the per netns .exit() handler for the connection tracker. This is clearly a chicken'n'egg problem: after the connection tracker .exit() handler, we've teared down all the connection tracking infrastructure already, so rightfully, xt_ct_tg_destroy() cannot be invoked at a later point in time during the netns cleanup, as that would lead to a use-after-free. At the same time, we cannot make x_tables depend on the connection tracker module, so that the xt_ct_tg_destroy() would be invoked earlier in the cleanup chain." Daniel confirms this has to do with the order in which modules are loaded or having compiled nf_conntrack as modules while x_tables built-in. So we have no guarantees regarding the order in which netns callbacks are executed. Fix this by allocating the templates through kmalloc() from the respective SYNPROXY and CT targets, so they don't depend on the conntrack kmem cache. Then, release then via nf_ct_tmpl_free() from destroy_conntrack(). This branch is marked as unlikely since conntrack templates are rarely allocated and only from the configuration plane path. Note that templates are not kept in any list to avoid further dependencies with nf_conntrack anymore, thus, the tmpl larval list is removed. Reported-by: Daniel Borkmann <daniel@iogearbox.net> Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org> Tested-by: Daniel Borkmann <daniel@iogearbox.net> |
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| .. | ||
| ipv4 | ||
| ipv6 | ||
| br_netfilter.h | ||
| nf_conntrack_acct.h | ||
| nf_conntrack_core.h | ||
| nf_conntrack_ecache.h | ||
| nf_conntrack_expect.h | ||
| nf_conntrack_extend.h | ||
| nf_conntrack_helper.h | ||
| nf_conntrack_l3proto.h | ||
| nf_conntrack_l4proto.h | ||
| nf_conntrack_labels.h | ||
| nf_conntrack_seqadj.h | ||
| nf_conntrack_synproxy.h | ||
| nf_conntrack_timeout.h | ||
| nf_conntrack_timestamp.h | ||
| nf_conntrack_tuple.h | ||
| nf_conntrack_zones.h | ||
| nf_conntrack.h | ||
| nf_log.h | ||
| nf_nat_core.h | ||
| nf_nat_helper.h | ||
| nf_nat_l3proto.h | ||
| nf_nat_l4proto.h | ||
| nf_nat_redirect.h | ||
| nf_nat.h | ||
| nf_queue.h | ||
| nf_tables_bridge.h | ||
| nf_tables_core.h | ||
| nf_tables_ipv4.h | ||
| nf_tables_ipv6.h | ||
| nf_tables.h | ||
| nfnetlink_log.h | ||
| nfnetlink_queue.h | ||
| nft_masq.h | ||
| nft_meta.h | ||
| nft_redir.h | ||
| nft_reject.h | ||
| xt_rateest.h | ||