Messages in this thread | | | Date | Wed, 24 May 2023 12:39:52 -0300 | Subject | Re: [PATCH v5 net 6/6] net/sched: qdisc_destroy() old ingress and clsact Qdiscs before grafting | From | Pedro Tammela <> |
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On 23/05/2023 22:20, Peilin Ye wrote: > From: Peilin Ye <peilin.ye@bytedance.com> > > 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@syzkaller.appspotmail.com > Closes: https://lore.kernel.org/r/0000000000006cf87705f79acf1a@google.com/ > Cc: Hillf Danton <hdanton@sina.com> > Cc: Vlad Buslov <vladbu@mellanox.com> > Signed-off-by: Peilin Ye <peilin.ye@bytedance.com>
Tested-by: Pedro Tammela <pctammela@mojatatu.com>
> --- > change in v5: > - reinitialize @q, @p (suggested by Vlad) and @tcm before replaying, > just like @flags in tc_new_tfilter() > > change in v3, v4: > - add in-body From: tag > > 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 | 40 ++++++++++++++++++++++++++++++--------- > net/sched/sch_generic.c | 14 +++++++++++--- > 3 files changed, 50 insertions(+), 12 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..286b7c58f5b9 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) > @@ -1450,19 +1464,22 @@ static int tc_get_qdisc(struct sk_buff *skb, struct nlmsghdr *n, > struct netlink_ext_ack *extack) > { > struct net *net = sock_net(skb->sk); > - struct tcmsg *tcm = nlmsg_data(n); > struct nlattr *tca[TCA_MAX + 1]; > struct net_device *dev; > + struct Qdisc *q, *p; > + struct tcmsg *tcm; > u32 clid; > - struct Qdisc *q = NULL; > - struct Qdisc *p = NULL; > int err; > > +replay: > err = nlmsg_parse_deprecated(n, sizeof(*tcm), tca, TCA_MAX, > rtm_tca_policy, extack); > if (err < 0) > return err; > > + tcm = nlmsg_data(n); > + q = p = NULL; > + > dev = __dev_get_by_index(net, tcm->tcm_ifindex); > if (!dev) > return -ENODEV; > @@ -1515,8 +1532,11 @@ 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 +1724,8 @@ 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);
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