Re: [PATCH net 6/6] net/sched: qdisc_destroy() old ingress and clsact Qdiscs before grafting

From: Jamal Hadi Salim
Date: Mon May 08 2023 - 07:33:35 EST

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On Fri, May 5, 2023 at 8:16 PM Peilin Ye <yepeilin.cs@xxxxxxxxx> wrote:
>
> 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-lockless RTM_{NEW,DEL,GET}TFILTER
> requests, when e.g. replacing ingress (clsact) Qdiscs, the old Qdisc could
> access the same miniq_{in,e}gress pointer(s) concurrently with the new
> Qdisc, causing race conditions [1] including a use-after-free 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
> ...
>
> The new (ingress or clsact) Qdisc should only call mini_qdisc_pair_swap()
> after the old Qdisc's last call (in {ingress,clsact}_destroy()) has
> finished.
>
> To achieve this, in qdisc_graft(), return -EBUSY if the old (ingress or
> clsact) Qdisc has ongoing RTNL-lockless 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-lockless filter requests. Introduce
> a non-static version of qdisc_destroy() that does a TCQ_F_BUILTIN check,
> just like qdisc_put() etc.
>
> [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-lockless)
> __tcf_qdisc_find(A) 10
> tcf_chain0_head_change(A)
> mini_qdisc_pair_swap(A) (1st)
> |
> | RTM_NEWQDISC (B, RTNL-locked)
> RCU 2 qdisc_graft(B)
> | 1 notify_and_destroy(A)
> |
> tcf_block_release(A) 0 RTM_NEWTFILTER (Y, RTNL-lockless)
> 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
> net_device::miniq_{in,e}gress pointers. The point is clear, however:
> B's first call to mini_qdisc_pair_swap() should take place after A's
> last call, in qdisc_destroy().
>
> 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@xxxxxxxxxxxxxxxxxxxxxxxxx
> Link: https://lore.kernel.org/netdev/0000000000006cf87705f79acf1a@xxxxxxxxxx
> Cc: Hillf Danton <hdanton@xxxxxxxx>
> Signed-off-by: Peilin Ye <peilin.ye@xxxxxxxxxxxxx>

Thanks for the excellent analysis Peilin and for chasing this to the
end. I have no doubt it was a lot of fun! ;->

Reviewed-by: Jamal Hadi Salim <jhs@xxxxxxxxxxxx>
Acked-by: Jamal Hadi Salim <jhs@xxxxxxxxxxxx>

cheers,
jamal

> ---
> include/net/sch_generic.h | 8 ++++++++
> net/sched/sch_api.c | 26 +++++++++++++++++++++-----
> net/sched/sch_generic.c | 14 +++++++++++---
> 3 files changed, 40 insertions(+), 8 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..a2d07bc8ded6 100644
> --- a/net/sched/sch_api.c
> +++ b/net/sched/sch_api.c
> @@ -1080,10 +1080,20 @@ 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;
> }
> +
> + /* This is the counterpart of that qdisc_refcount_inc_nz() call in
> + * __tcf_qdisc_find() for RTNL-lockless filter requests.
> + */
> + if (!qdisc_refcount_dec_if_one(dev_queue->qdisc_sleeping)) {
> + NL_SET_ERR_MSG(extack,
> + "Current ingress or clsact Qdisc has ongoing filter request(s)");
> + return -EBUSY;
> + }
> }
>
> if (dev->flags & IFF_UP)
> @@ -1104,8 +1114,16 @@ 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 +1137,6 @@ 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 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
>

Next message: Dmitry Baryshkov: "Re: [PATCH] clk: qcom: mmcc-msm8974: Add OXILICX_GDSC for msm8226"
Previous message: Sascha Hauer: "Re: [PATCH 07/11] leds: trigger: netdev: reject interval and device store for hw_control"
Next in thread: Peilin Ye: "Re: [PATCH net 6/6] net/sched: qdisc_destroy() old ingress and clsact Qdiscs before grafting"
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