6.9-stable review patch. If anyone has any objections, please let me know.
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From: Daniel Borkmann daniel@iogearbox.net
[ Upstream commit 1cb6f0bae50441f4b4b32a28315853b279c7404e ]
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: e420bed02507 ("bpf: Add fd-based tcx multi-prog infra with link support") Reported-by: Pedro Pinto xten@osec.io Co-developed-by: Pedro Pinto xten@osec.io Signed-off-by: Pedro Pinto xten@osec.io Signed-off-by: Daniel Borkmann daniel@iogearbox.net Cc: Hyunwoo Kim v4bel@theori.io Cc: Wongi Lee qwerty@theori.io Cc: Martin KaFai Lau martin.lau@kernel.org Link: https://lore.kernel.org/r/20240708133130.11609-1-daniel@iogearbox.net Signed-off-by: Martin KaFai Lau martin.lau@kernel.org Signed-off-by: Sasha Levin sashal@kernel.org --- include/net/tcx.h | 13 +++++++++---- net/sched/sch_ingress.c | 12 ++++++------ 2 files changed, 15 insertions(+), 10 deletions(-)
diff --git a/include/net/tcx.h b/include/net/tcx.h index 04be9377785d7..0a5f40a91c42f 100644 --- a/include/net/tcx.h +++ b/include/net/tcx.h @@ -13,7 +13,7 @@ struct mini_Qdisc; struct tcx_entry { struct mini_Qdisc __rcu *miniq; struct bpf_mprog_bundle bundle; - bool miniq_active; + u32 miniq_active; struct rcu_head rcu; };
@@ -124,11 +124,16 @@ static inline void tcx_skeys_dec(bool ingress) tcx_dec(); }
-static inline void tcx_miniq_set_active(struct bpf_mprog_entry *entry, - const bool active) +static inline void tcx_miniq_inc(struct bpf_mprog_entry *entry) { ASSERT_RTNL(); - tcx_entry(entry)->miniq_active = active; + tcx_entry(entry)->miniq_active++; +} + +static inline void tcx_miniq_dec(struct bpf_mprog_entry *entry) +{ + ASSERT_RTNL(); + tcx_entry(entry)->miniq_active--; }
static inline bool tcx_entry_is_active(struct bpf_mprog_entry *entry) diff --git a/net/sched/sch_ingress.c b/net/sched/sch_ingress.c index c2ef9dcf91d2d..cc6051d4f2ef8 100644 --- a/net/sched/sch_ingress.c +++ b/net/sched/sch_ingress.c @@ -91,7 +91,7 @@ static int ingress_init(struct Qdisc *sch, struct nlattr *opt, entry = tcx_entry_fetch_or_create(dev, true, &created); if (!entry) return -ENOMEM; - tcx_miniq_set_active(entry, true); + tcx_miniq_inc(entry); mini_qdisc_pair_init(&q->miniqp, sch, &tcx_entry(entry)->miniq); if (created) tcx_entry_update(dev, entry, true); @@ -121,7 +121,7 @@ static void ingress_destroy(struct Qdisc *sch) tcf_block_put_ext(q->block, sch, &q->block_info);
if (entry) { - tcx_miniq_set_active(entry, false); + tcx_miniq_dec(entry); if (!tcx_entry_is_active(entry)) { tcx_entry_update(dev, NULL, true); tcx_entry_free(entry); @@ -257,7 +257,7 @@ static int clsact_init(struct Qdisc *sch, struct nlattr *opt, entry = tcx_entry_fetch_or_create(dev, true, &created); if (!entry) return -ENOMEM; - tcx_miniq_set_active(entry, true); + tcx_miniq_inc(entry); mini_qdisc_pair_init(&q->miniqp_ingress, sch, &tcx_entry(entry)->miniq); if (created) tcx_entry_update(dev, entry, true); @@ -276,7 +276,7 @@ static int clsact_init(struct Qdisc *sch, struct nlattr *opt, entry = tcx_entry_fetch_or_create(dev, false, &created); if (!entry) return -ENOMEM; - tcx_miniq_set_active(entry, true); + tcx_miniq_inc(entry); mini_qdisc_pair_init(&q->miniqp_egress, sch, &tcx_entry(entry)->miniq); if (created) tcx_entry_update(dev, entry, false); @@ -302,7 +302,7 @@ static void clsact_destroy(struct Qdisc *sch) tcf_block_put_ext(q->egress_block, sch, &q->egress_block_info);
if (ingress_entry) { - tcx_miniq_set_active(ingress_entry, false); + tcx_miniq_dec(ingress_entry); if (!tcx_entry_is_active(ingress_entry)) { tcx_entry_update(dev, NULL, true); tcx_entry_free(ingress_entry); @@ -310,7 +310,7 @@ static void clsact_destroy(struct Qdisc *sch) }
if (egress_entry) { - tcx_miniq_set_active(egress_entry, false); + tcx_miniq_dec(egress_entry); if (!tcx_entry_is_active(egress_entry)) { tcx_entry_update(dev, NULL, false); tcx_entry_free(egress_entry);