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Message-ID: <aHQmajPF7eAZw3qi@xps>
Date: Sun, 13 Jul 2025 14:34:34 -0700
From: Xiang Mei <xmei5@....edu>
To: Cong Wang <xiyou.wangcong@...il.com>
Cc: netdev@...r.kernel.org, gregkh@...uxfoundation.org, jhs@...atatu.com,
	jiri@...nulli.us, security@...nel.org
Subject: Re: [PATCH v3] net/sched: sch_qfq: Fix race condition on
 qfq_aggregate

On Sun, Jul 13, 2025 at 02:31:34PM -0700, Cong Wang wrote:
> Hi Xiang,
> 
> It looks like your patch caused the following NULL-ptr-deref. I
> triggered it when running command `./tdc.py -f tc-tests/infra/qdiscs.json`
> 
> Could you take a look? I don't have much time now, since I am still
> finalizing my netem duplicate patches.
> 
> Thanks!
Thanks for the information to reproduce. Working on tracing it.
> 
> ------------------------------------>
> 
> Test 5e6d: Test QFQ's enqueue reentrant behaviour with netem
> [ 1066.410119] ==================================================================
> [ 1066.411114] BUG: KASAN: null-ptr-deref in qfq_dequeue+0x1e4/0x5a1
> [ 1066.412305] Read of size 8 at addr 0000000000000048 by task ping/945
> [ 1066.413136]
> [ 1066.413426] CPU: 0 UID: 0 PID: 945 Comm: ping Tainted: G        W           6.16.0-rc5+ #542 PREEMPT(voluntary)
> [ 1066.413459] Tainted: [W]=WARN
> [ 1066.413468] Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS 1.15.0-1 04/01/2014
> [ 1066.413476] Call Trace:
> [ 1066.413499]  <TASK>
> [ 1066.413502]  dump_stack_lvl+0x65/0x90
> [ 1066.413502]  kasan_report+0x85/0xab
> [ 1066.413502]  ? qfq_dequeue+0x1e4/0x5a1
> [ 1066.413502]  qfq_dequeue+0x1e4/0x5a1
> [ 1066.413502]  ? __pfx_qfq_dequeue+0x10/0x10
> [ 1066.413502]  ? srso_return_thunk+0x5/0x5f
> [ 1066.413502]  ? lock_acquired+0xde/0x10b
> [ 1066.413502]  ? srso_return_thunk+0x5/0x5f
> [ 1066.413502]  ? sch_direct_xmit+0x1a7/0x390
> [ 1066.413502]  ? __pfx_sch_direct_xmit+0x10/0x10
> [ 1066.413502]  dequeue_skb+0x411/0x7a8
> [ 1066.413502]  __qdisc_run+0x94/0x193
> [ 1066.413502]  ? __pfx___qdisc_run+0x10/0x10
> [ 1066.413502]  ? find_held_lock+0x2b/0x71
> [ 1066.413502]  ? __dev_xmit_skb+0x27c/0x45e
> [ 1066.413502]  ? srso_return_thunk+0x5/0x5f
> [ 1066.413502]  ? rcu_is_watching+0x1c/0x3c
> [ 1066.413502]  ? srso_return_thunk+0x5/0x5f
> [ 1066.413502]  ? dev_qdisc_enqueue+0x117/0x14c
> [ 1066.413502]  __dev_xmit_skb+0x3b9/0x45e
> [ 1066.413502]  ? __pfx___dev_xmit_skb+0x10/0x10
> [ 1066.413502]  ? srso_return_thunk+0x5/0x5f
> [ 1066.413502]  ? __pfx_rcu_read_lock_bh_held+0x10/0x10
> [ 1066.413502]  ? srso_return_thunk+0x5/0x5f
> [ 1066.413502]  __dev_queue_xmit+0xa14/0xbe2
> [ 1066.413502]  ? look_up_lock_class+0xb0/0x10d
> [ 1066.413502]  ? __pfx___dev_queue_xmit+0x10/0x10
> [ 1066.413502]  ? validate_chain+0x4b/0x261
> [ 1066.413502]  ? srso_return_thunk+0x5/0x5f
> [ 1066.413502]  ? __lock_acquire+0x71d/0x7b1
> [ 1066.413502]  ? neigh_resolve_output+0x13b/0x1d7
> [ 1066.413502]  ? srso_return_thunk+0x5/0x5f
> [ 1066.413502]  ? lock_acquire.part.0+0xb0/0x1c6
> [ 1066.413502]  ? srso_return_thunk+0x5/0x5f
> [ 1066.413502]  ? find_held_lock+0x2b/0x71
> [ 1066.413502]  ? srso_return_thunk+0x5/0x5f
> [ 1066.413502]  ? local_clock_noinstr+0x32/0x9c
> [ 1066.413502]  ? srso_return_thunk+0x5/0x5f
> [ 1066.413502]  ? srso_return_thunk+0x5/0x5f
> [ 1066.413502]  ? mark_lock+0x6d/0x14d
> [ 1066.413502]  ? srso_return_thunk+0x5/0x5f
> [ 1066.413502]  ? __asan_memcpy+0x38/0x59
> [ 1066.413502]  ? srso_return_thunk+0x5/0x5f
> [ 1066.413502]  ? eth_header+0x92/0xd1
> [ 1066.413502]  ? srso_return_thunk+0x5/0x5f
> [ 1066.413502]  ? neigh_resolve_output+0x188/0x1d7
> [ 1066.413502]  ip_finish_output2+0x58b/0x5c3
> [ 1066.413502]  ip_send_skb+0x25/0x5f
> [ 1066.413502]  raw_sendmsg+0x9dc/0xb60
> [ 1066.413502]  ? __pfx_raw_sendmsg+0x10/0x10
> [ 1066.413502]  ? srso_return_thunk+0x5/0x5f
> [ 1066.413502]  ? stack_trace_save+0x8b/0xbb
> [ 1066.413502]  ? kasan_save_stack+0x1c/0x38
> [ 1066.413502]  ? kasan_record_aux_stack+0x87/0x91
> [ 1066.413502]  ? __might_fault+0x72/0xbe
> [ 1066.413502]  ? __ww_mutex_die.part.0+0xe/0x88
> [ 1066.413502]  ? __might_fault+0x72/0xbe
> [ 1066.413502]  ? srso_return_thunk+0x5/0x5f
> [ 1066.413502]  ? find_held_lock+0x2b/0x71
> [ 1066.413502]  ? srso_return_thunk+0x5/0x5f
> [ 1066.413502]  ? local_clock_noinstr+0x32/0x9c
> [ 1066.413502]  ? srso_return_thunk+0x5/0x5f
> [ 1066.413502]  ? srso_return_thunk+0x5/0x5f
> [ 1066.413502]  ? __lock_release.isra.0+0xdb/0x197
> [ 1066.413502]  ? __might_fault+0x72/0xbe
> [ 1066.413502]  ? srso_return_thunk+0x5/0x5f
> [ 1066.413502]  ? inet_send_prepare+0x18/0x5d
> [ 1066.413502]  sock_sendmsg_nosec+0x82/0xe2
> [ 1066.413502]  __sys_sendto+0x175/0x1cc
> [ 1066.413502]  ? __pfx___sys_sendto+0x10/0x10
> [ 1066.413502]  ? srso_return_thunk+0x5/0x5f
> [ 1066.413502]  ? __might_fault+0x72/0xbe
> [ 1066.413502]  ? srso_return_thunk+0x5/0x5f
> [ 1066.413502]  ? local_clock_noinstr+0x32/0x9c
> [ 1066.413502]  ? srso_return_thunk+0x5/0x5f
> [ 1066.413502]  ? srso_return_thunk+0x5/0x5f
> [ 1066.413502]  ? __lock_release.isra.0+0xdb/0x197
> [ 1066.413502]  ? __might_fault+0x72/0xbe
> [ 1066.413502]  ? srso_return_thunk+0x5/0x5f
> [ 1066.413502]  ? lock_release+0xde/0x10b
> [ 1066.413502]  ? srso_return_thunk+0x5/0x5f
> [ 1066.413502]  ? __do_sys_gettimeofday+0xb3/0x112
> [ 1066.413502]  __x64_sys_sendto+0x76/0x86
> [ 1066.413502]  do_syscall_64+0x94/0x209
> [ 1066.413502]  entry_SYSCALL_64_after_hwframe+0x76/0x7e
> [ 1066.413502] RIP: 0033:0x7fb9f917ce27
> [ 1066.413502] Code: c7 c0 ff ff ff ff eb be 66 2e 0f 1f 84 00 00 00 00 00 90 f3 0f 1e fa 80 3d 45 85 0c 00 00 41 89 ca 74 10 b8 2c 00 00 00 0f 05 <48> 3d 00 f0 ff ff 77 69 c3 55 48 89 e5 53 48 83 ec 38 44 89 4d d0
> [ 1066.413502] RSP: 002b:00007ffeb9932798 EFLAGS: 00000202 ORIG_RAX: 000000000000002c
> [ 1066.413502] RAX: ffffffffffffffda RBX: 000056476e3550a0 RCX: 00007fb9f917ce27
> [ 1066.413502] RDX: 0000000000000040 RSI: 000056476ea11320 RDI: 0000000000000003
> [ 1066.413502] RBP: 00007ffeb99327e0 R08: 000056476e357320 R09: 0000000000000010
> [ 1066.413502] R10: 0000000000000000 R11: 0000000000000202 R12: 000056476ea11320
> [ 1066.413502] R13: 0000000000000040 R14: 00007ffeb9933e98 R15: 00007ffeb9933e98
> [ 1066.413502]  </TASK>
> [ 1066.413502] ==================================================================
>

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