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Message-ID: <CAM0EoMkEL+o-u3-NM8fYcZbynzbbSWdMofVLC-56YvxsUOGA-A@mail.gmail.com>
Date: Tue, 13 Jun 2023 08:07:37 -0400
From: Jamal Hadi Salim <jhs@...atatu.com>
To: Peilin Ye <yepeilin.cs@...il.com>
Cc: Cong Wang <xiyou.wangcong@...il.com>, Jiri Pirko <jiri@...nulli.us>,
"David S. Miller" <davem@...emloft.net>, Eric Dumazet <edumazet@...gle.com>,
Jakub Kicinski <kuba@...nel.org>, Paolo Abeni <pabeni@...hat.com>, Peilin Ye <peilin.ye@...edance.com>,
Vlad Buslov <vladbu@...lanox.com>, Pedro Tammela <pctammela@...atatu.com>,
John Fastabend <john.fastabend@...il.com>, Daniel Borkmann <daniel@...earbox.net>,
Hillf Danton <hdanton@...a.com>, Zhengchao Shao <shaozhengchao@...wei.com>, netdev@...r.kernel.org,
linux-kernel@...r.kernel.org, Cong Wang <cong.wang@...edance.com>
Subject: Re: [PATCH net 2/2] net/sched: qdisc_destroy() old ingress and clsact
Qdiscs before grafting
On Sat, Jun 10, 2023 at 11:30 PM Peilin Ye <yepeilin.cs@...il.com> wrote:
>
> From: Peilin Ye <peilin.ye@...edance.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 {ingress,clsact}_destroy()) has
> finished:
>
> In qdisc_graft(), return -EBUSY if @old has any ongoing 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 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 commit c7cfbd115001 ("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 just one of the possible consequences of concurrently accessing
> miniq_{in,e}gress pointers.
>
> 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>
Acked-by: Jamal Hadi Salim <jhs@...atatu.com>
cheers,
jamal
> ---
> include/net/sch_generic.h | 8 ++++++++
> net/sched/sch_api.c | 28 +++++++++++++++++++++++-----
> net/sched/sch_generic.c | 14 +++++++++++---
> 3 files changed, 42 insertions(+), 8 deletions(-)
>
> diff --git a/include/net/sch_generic.h b/include/net/sch_generic.h
> index 27271f2b37cb..12eadecf8cd0 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 094ca3a5b633..aa6b1fe65151 100644
> --- a/net/sched/sch_api.c
> +++ b/net/sched/sch_api.c
> @@ -1086,10 +1086,22 @@ 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;
> }
> +
> + q = rtnl_dereference(dev_queue->qdisc_sleeping);
> +
> + /* This is the counterpart of that qdisc_refcount_inc_nz() call in
> + * __tcf_qdisc_find() for filter requests.
> + */
> + if (!qdisc_refcount_dec_if_one(q)) {
> + NL_SET_ERR_MSG(extack,
> + "Current ingress or clsact Qdisc has ongoing filter requests");
> + return -EBUSY;
> + }
> }
>
> if (dev->flags & IFF_UP)
> @@ -1110,8 +1122,16 @@ 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:
> @@ -1125,8 +1145,6 @@ 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)
> diff --git a/net/sched/sch_generic.c b/net/sched/sch_generic.c
> index 3248259eba32..5d7e23f4cc0e 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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