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Message-Id: <8e3383d0bacd084f0e33d9158d24bd411f1bf6ba.1684796705.git.peilin.ye@bytedance.com> Date: Mon, 22 May 2023 16:55:36 -0700 From: Peilin Ye <yepeilin.cs@...il.com> To: "David S. Miller" <davem@...emloft.net>, Eric Dumazet <edumazet@...gle.com>, Jakub Kicinski <kuba@...nel.org>, Paolo Abeni <pabeni@...hat.com>, Jamal Hadi Salim <jhs@...atatu.com>, Cong Wang <xiyou.wangcong@...il.com>, Jiri Pirko <jiri@...nulli.us> Cc: Peilin Ye <peilin.ye@...edance.com>, Daniel Borkmann <daniel@...earbox.net>, John Fastabend <john.fastabend@...il.com>, Vlad Buslov <vladbu@...lanox.com>, Pedro Tammela <pctammela@...atatu.com>, Hillf Danton <hdanton@...a.com>, netdev@...r.kernel.org, linux-kernel@...r.kernel.org, Cong Wang <cong.wang@...edance.com>, Peilin Ye <yepeilin.cs@...il.com> Subject: [PATCH v2 net 6/6] net/sched: qdisc_destroy() old ingress and clsact Qdiscs before grafting mini_Qdisc_pair::p_miniq is a double pointer to mini_Qdisc, initialized in ingress_init() to point to net_device::miniq_ingress. ingress Qdiscs access this per-net_device pointer in mini_qdisc_pair_swap(). Similar for clsact Qdiscs and miniq_egress. Unfortunately, after introducing RTNL-unlocked RTM_{NEW,DEL,GET}TFILTER requests (thanks Hillf Danton for the hint), when replacing ingress or clsact Qdiscs, for example, the old Qdisc ("@old") could access the same miniq_{in,e}gress pointer(s) concurrently with the new Qdisc ("@new"), causing race conditions [1] including a use-after-free bug in mini_qdisc_pair_swap() reported by syzbot: BUG: KASAN: slab-use-after-free in mini_qdisc_pair_swap+0x1c2/0x1f0 net/sched/sch_generic.c:1573 Write of size 8 at addr ffff888045b31308 by task syz-executor690/14901 ... Call Trace: <TASK> __dump_stack lib/dump_stack.c:88 [inline] dump_stack_lvl+0xd9/0x150 lib/dump_stack.c:106 print_address_description.constprop.0+0x2c/0x3c0 mm/kasan/report.c:319 print_report mm/kasan/report.c:430 [inline] kasan_report+0x11c/0x130 mm/kasan/report.c:536 mini_qdisc_pair_swap+0x1c2/0x1f0 net/sched/sch_generic.c:1573 tcf_chain_head_change_item net/sched/cls_api.c:495 [inline] tcf_chain0_head_change.isra.0+0xb9/0x120 net/sched/cls_api.c:509 tcf_chain_tp_insert net/sched/cls_api.c:1826 [inline] tcf_chain_tp_insert_unique net/sched/cls_api.c:1875 [inline] tc_new_tfilter+0x1de6/0x2290 net/sched/cls_api.c:2266 ... @old and @new should not affect each other. In other words, @old should never modify miniq_{in,e}gress after @new, and @new should not update @old's RCU state. Fixing without changing sch_api.c turned out to be difficult (please refer to Closes: for discussions). Instead, make sure @new's first call always happen after @old's last call, in qdisc_destroy(), has finished: In qdisc_graft(), return -EAGAIN and tell the caller to replay (suggested by Vlad Buslov) if @old has any ongoing RTNL-unlocked filter requests, and call qdisc_destroy() for @old before grafting @new. Introduce qdisc_refcount_dec_if_one() as the counterpart of qdisc_refcount_inc_nz() used for RTNL-unlocked filter requests. Introduce a non-static version of qdisc_destroy() that does a TCQ_F_BUILTIN check, just like qdisc_put() etc. Depends on patch "net/sched: Refactor qdisc_graft() for ingress and clsact Qdiscs". [1] To illustrate, the syzkaller reproducer adds ingress Qdiscs under TC_H_ROOT (no longer possible after patch "net/sched: sch_ingress: Only create under TC_H_INGRESS") on eth0 that has 8 transmission queues: Thread 1 creates ingress Qdisc A (containing mini Qdisc a1 and a2), then adds a flower filter X to A. Thread 2 creates another ingress Qdisc B (containing mini Qdisc b1 and b2) to replace A, then adds a flower filter Y to B. Thread 1 A's refcnt Thread 2 RTM_NEWQDISC (A, RTNL-locked) qdisc_create(A) 1 qdisc_graft(A) 9 RTM_NEWTFILTER (X, RTNL-unlocked) __tcf_qdisc_find(A) 10 tcf_chain0_head_change(A) mini_qdisc_pair_swap(A) (1st) | | RTM_NEWQDISC (B, RTNL-locked) RCU sync 2 qdisc_graft(B) | 1 notify_and_destroy(A) | tcf_block_release(A) 0 RTM_NEWTFILTER (Y, RTNL-unlocked) qdisc_destroy(A) tcf_chain0_head_change(B) tcf_chain0_head_change_cb_del(A) mini_qdisc_pair_swap(B) (2nd) mini_qdisc_pair_swap(A) (3rd) | ... ... Here, B calls mini_qdisc_pair_swap(), pointing eth0->miniq_ingress to its mini Qdisc, b1. Then, A calls mini_qdisc_pair_swap() again during ingress_destroy(), setting eth0->miniq_ingress to NULL, so ingress packets on eth0 will not find filter Y in sch_handle_ingress(). This is only one of the possible consequences of concurrently accessing miniq_{in,e}gress pointers. The point is clear though: again, A should never modify those per-net_device pointers after B, and B should not update A's RCU state. Fixes: 7a096d579e8e ("net: sched: ingress: set 'unlocked' flag for Qdisc ops") Fixes: 87f373921c4e ("net: sched: ingress: set 'unlocked' flag for clsact Qdisc ops") Reported-by: syzbot+b53a9c0d1ea4ad62da8b@...kaller.appspotmail.com Closes: https://lore.kernel.org/r/0000000000006cf87705f79acf1a@google.com/ Cc: Hillf Danton <hdanton@...a.com> Cc: Vlad Buslov <vladbu@...lanox.com> Signed-off-by: Peilin Ye <peilin.ye@...edance.com> --- changes in v2: - replay the request if the current Qdisc has any ongoing RTNL-unlocked filter requests (Vlad) - minor changes in code comments and commit log include/net/sch_generic.h | 8 ++++++++ net/sched/sch_api.c | 32 ++++++++++++++++++++++++++------ net/sched/sch_generic.c | 14 +++++++++++--- 3 files changed, 45 insertions(+), 9 deletions(-) diff --git a/include/net/sch_generic.h b/include/net/sch_generic.h index fab5ba3e61b7..3e9cc43cbc90 100644 --- a/include/net/sch_generic.h +++ b/include/net/sch_generic.h @@ -137,6 +137,13 @@ static inline void qdisc_refcount_inc(struct Qdisc *qdisc) refcount_inc(&qdisc->refcnt); } +static inline bool qdisc_refcount_dec_if_one(struct Qdisc *qdisc) +{ + if (qdisc->flags & TCQ_F_BUILTIN) + return true; + return refcount_dec_if_one(&qdisc->refcnt); +} + /* Intended to be used by unlocked users, when concurrent qdisc release is * possible. */ @@ -652,6 +659,7 @@ void dev_deactivate_many(struct list_head *head); struct Qdisc *dev_graft_qdisc(struct netdev_queue *dev_queue, struct Qdisc *qdisc); void qdisc_reset(struct Qdisc *qdisc); +void qdisc_destroy(struct Qdisc *qdisc); void qdisc_put(struct Qdisc *qdisc); void qdisc_put_unlocked(struct Qdisc *qdisc); void qdisc_tree_reduce_backlog(struct Qdisc *qdisc, int n, int len); diff --git a/net/sched/sch_api.c b/net/sched/sch_api.c index f72a581666a2..b3bafa6c1b44 100644 --- a/net/sched/sch_api.c +++ b/net/sched/sch_api.c @@ -1080,10 +1080,18 @@ static int qdisc_graft(struct net_device *dev, struct Qdisc *parent, if ((q && q->flags & TCQ_F_INGRESS) || (new && new->flags & TCQ_F_INGRESS)) { ingress = 1; - if (!dev_ingress_queue(dev)) { + dev_queue = dev_ingress_queue(dev); + if (!dev_queue) { NL_SET_ERR_MSG(extack, "Device does not have an ingress queue"); return -ENOENT; } + + /* Replay if the current ingress (or clsact) Qdisc has ongoing + * RTNL-unlocked filter request(s). This is the counterpart of that + * qdisc_refcount_inc_nz() call in __tcf_qdisc_find(). + */ + if (!qdisc_refcount_dec_if_one(dev_queue->qdisc_sleeping)) + return -EAGAIN; } if (dev->flags & IFF_UP) @@ -1104,8 +1112,16 @@ static int qdisc_graft(struct net_device *dev, struct Qdisc *parent, qdisc_put(old); } } else { - dev_queue = dev_ingress_queue(dev); - old = dev_graft_qdisc(dev_queue, new); + old = dev_graft_qdisc(dev_queue, NULL); + + /* {ingress,clsact}_destroy() @old before grafting @new to avoid + * unprotected concurrent accesses to net_device::miniq_{in,e}gress + * pointer(s) in mini_qdisc_pair_swap(). + */ + qdisc_notify(net, skb, n, classid, old, new, extack); + qdisc_destroy(old); + + dev_graft_qdisc(dev_queue, new); } skip: @@ -1119,8 +1135,6 @@ static int qdisc_graft(struct net_device *dev, struct Qdisc *parent, if (new && new->ops->attach) new->ops->attach(new); - } else { - notify_and_destroy(net, skb, n, classid, old, new, extack); } if (dev->flags & IFF_UP) @@ -1458,6 +1472,7 @@ static int tc_get_qdisc(struct sk_buff *skb, struct nlmsghdr *n, struct Qdisc *p = NULL; int err; +replay: err = nlmsg_parse_deprecated(n, sizeof(*tcm), tca, TCA_MAX, rtm_tca_policy, extack); if (err < 0) @@ -1515,8 +1530,11 @@ static int tc_get_qdisc(struct sk_buff *skb, struct nlmsghdr *n, return -ENOENT; } err = qdisc_graft(dev, p, skb, n, clid, NULL, q, extack); - if (err != 0) + if (err != 0) { + if (err == -EAGAIN) + goto replay; return err; + } } else { qdisc_notify(net, skb, n, clid, NULL, q, NULL); } @@ -1704,6 +1722,8 @@ static int tc_modify_qdisc(struct sk_buff *skb, struct nlmsghdr *n, if (err) { if (q) qdisc_put(q); + if (err == -EAGAIN) + goto replay; return err; } diff --git a/net/sched/sch_generic.c b/net/sched/sch_generic.c index 37e41f972f69..e14ed47f961c 100644 --- a/net/sched/sch_generic.c +++ b/net/sched/sch_generic.c @@ -1046,7 +1046,7 @@ static void qdisc_free_cb(struct rcu_head *head) qdisc_free(q); } -static void qdisc_destroy(struct Qdisc *qdisc) +static void __qdisc_destroy(struct Qdisc *qdisc) { const struct Qdisc_ops *ops = qdisc->ops; @@ -1070,6 +1070,14 @@ static void qdisc_destroy(struct Qdisc *qdisc) call_rcu(&qdisc->rcu, qdisc_free_cb); } +void qdisc_destroy(struct Qdisc *qdisc) +{ + if (qdisc->flags & TCQ_F_BUILTIN) + return; + + __qdisc_destroy(qdisc); +} + void qdisc_put(struct Qdisc *qdisc) { if (!qdisc) @@ -1079,7 +1087,7 @@ void qdisc_put(struct Qdisc *qdisc) !refcount_dec_and_test(&qdisc->refcnt)) return; - qdisc_destroy(qdisc); + __qdisc_destroy(qdisc); } EXPORT_SYMBOL(qdisc_put); @@ -1094,7 +1102,7 @@ void qdisc_put_unlocked(struct Qdisc *qdisc) !refcount_dec_and_rtnl_lock(&qdisc->refcnt)) return; - qdisc_destroy(qdisc); + __qdisc_destroy(qdisc); rtnl_unlock(); } EXPORT_SYMBOL(qdisc_put_unlocked); -- 2.20.1
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