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Pedro Pinto and later independently also Hyunwoo Kim and Wongi Lee reported
an issue that the tcx_entry can be released too early leading to a use
after free (UAF) when an active old-style ingress or clsact qdisc with a
shared tc block is later replaced by another ingress or clsact instance.
Essentially, the sequence to trigger the UAF (one example) can be as follows:
1. A network namespace is created
2. An ingress qdisc is created. This allocates a tcx_entry, and
&tcx_entry->miniq is stored in the qdisc's miniqp->p_miniq. At the
same time, a tcf block with index 1 is created.
3. chain0 is attached to the tcf block. chain0 must be connected to
the block linked to the ingress qdisc to later reach the function
tcf_chain0_head_change_cb_del() which triggers the UAF.
4. Create and graft a clsact qdisc. This causes the ingress qdisc
created in step 1 to be removed, thus freeing the previously linked
tcx_entry:
rtnetlink_rcv_msg()
=> tc_modify_qdisc()
=> qdisc_create()
=> clsact_init() [a]
=> qdisc_graft()
=> qdisc_destroy()
=> __qdisc_destroy()
=> ingress_destroy() [b]
=> tcx_entry_free()
=> kfree_rcu() // tcx_entry freed
5. Finally, the network namespace is closed. This registers the
cleanup_net worker, and during the process of releasing the
remaining clsact qdisc, it accesses the tcx_entry that was
already freed in step 4, causing the UAF to occur:
cleanup_net()
=> ops_exit_list()
=> default_device_exit_batch()
=> unregister_netdevice_many()
=> unregister_netdevice_many_notify()
=> dev_shutdown()
=> qdisc_put()
=> clsact_destroy() [c]
=> tcf_block_put_ext()
=> tcf_chain0_head_change_cb_del()
=> tcf_chain_head_change_item()
=> clsact_chain_head_change()
=> mini_qdisc_pair_swap() // UAF
There are also other variants, the gist is to add an ingress (or clsact)
qdisc with a specific shared block, then to replace that qdisc, waiting
for the tcx_entry kfree_rcu() to be executed and subsequently accessing
the current active qdisc's miniq one way or another.
The correct fix is to turn the miniq_active boolean into a counter. What
can be observed, at step 2 above, the counter transitions from 0->1, at
step [a] from 1->2 (in order for the miniq object to remain active during
the replacement), then in [b] from 2->1 and finally [c] 1->0 with the
eventual release. The reference counter in general ranges from [0,2] and
it does not need to be atomic since all access to the counter is protected
by the rtnl mutex. With this in place, there is no longer a UAF happening
and the tcx_entry is freed at the correct time.
Fixes:
|
||
|---|---|---|
| .. | ||
| act_api.c | ||
| act_bpf.c | ||
| act_connmark.c | ||
| act_csum.c | ||
| act_ct.c | ||
| act_ctinfo.c | ||
| act_gact.c | ||
| act_gate.c | ||
| act_ife.c | ||
| act_meta_mark.c | ||
| act_meta_skbprio.c | ||
| act_meta_skbtcindex.c | ||
| act_mirred.c | ||
| act_mpls.c | ||
| act_nat.c | ||
| act_pedit.c | ||
| act_police.c | ||
| act_sample.c | ||
| act_simple.c | ||
| act_skbedit.c | ||
| act_skbmod.c | ||
| act_tunnel_key.c | ||
| act_vlan.c | ||
| cls_api.c | ||
| cls_basic.c | ||
| cls_bpf.c | ||
| cls_cgroup.c | ||
| cls_flow.c | ||
| cls_flower.c | ||
| cls_fw.c | ||
| cls_matchall.c | ||
| cls_route.c | ||
| cls_u32.c | ||
| em_canid.c | ||
| em_cmp.c | ||
| em_ipset.c | ||
| em_ipt.c | ||
| em_meta.c | ||
| em_nbyte.c | ||
| em_text.c | ||
| em_u32.c | ||
| ematch.c | ||
| Kconfig | ||
| Makefile | ||
| sch_api.c | ||
| sch_blackhole.c | ||
| sch_cake.c | ||
| sch_cbs.c | ||
| sch_choke.c | ||
| sch_codel.c | ||
| sch_drr.c | ||
| sch_etf.c | ||
| sch_ets.c | ||
| sch_fifo.c | ||
| sch_fq_codel.c | ||
| sch_fq_pie.c | ||
| sch_fq.c | ||
| sch_frag.c | ||
| sch_generic.c | ||
| sch_gred.c | ||
| sch_hfsc.c | ||
| sch_hhf.c | ||
| sch_htb.c | ||
| sch_ingress.c | ||
| sch_mq.c | ||
| sch_mqprio_lib.c | ||
| sch_mqprio_lib.h | ||
| sch_mqprio.c | ||
| sch_multiq.c | ||
| sch_netem.c | ||
| sch_pie.c | ||
| sch_plug.c | ||
| sch_prio.c | ||
| sch_qfq.c | ||
| sch_red.c | ||
| sch_sfb.c | ||
| sch_sfq.c | ||
| sch_skbprio.c | ||
| sch_taprio.c | ||
| sch_tbf.c | ||
| sch_teql.c | ||