Date:   Mon, 23 Jan 2017 11:23:48 +0100
From:   Dmitry Vyukov <dvyukov@...gle.com>
To:     David Miller <davem@...emloft.net>,
        Alexey Kuznetsov <kuznet@....inr.ac.ru>,
        James Morris <jmorris@...ei.org>,
        Hideaki YOSHIFUJI <yoshfuji@...ux-ipv6.org>,
        Patrick McHardy <kaber@...sh.net>,
        netdev <netdev@...r.kernel.org>,
        LKML <linux-kernel@...r.kernel.org>,
        Eric Dumazet <edumazet@...gle.com>
Cc:     syzkaller <syzkaller@...glegroups.com>
Subject: Re: net: use-after-free in tw_timer_handler

On Mon, Jan 23, 2017 at 11:19 AM, Dmitry Vyukov <dvyukov@...gle.com> wrote:
> Hello,
>
> While running syzkaller fuzzer I started seeing use-after-frees in
> tw_timer_handler. It happens with very low frequency, so far I've seen
> 22 of them. But all reports look consistent, so I would assume that it
> is real, just requires a very tricky race to happen. I've stared
> seeing it around Jan 17, however I did not update kernels for some
> time before that so potentially the issues was introduced somewhat
> earlier. Or maybe fuzzer just figured how to trigger it, and the bug
> is actually old. I am seeing it on all of torvalds/linux-next/mmotm,
> some commits if it matters: 7a308bb3016f57e5be11a677d15b821536419d36,
> 5cf7a0f3442b2312326c39f571d637669a478235,
> c497f8d17246720afe680ea1a8fa6e48e75af852.
> Majority of reports points to net_drop_ns as the offending free, but
> it may be red herring. Since the access happens in timer, it can
> happen long after free and the memory could have been reused. I've
> also seen few where the access in tw_timer_handler is reported as
> out-of-bounds on task_struct and on struct filename.



I've briefly skimmed through the code. Assuming that it requires a
very tricky race to be triggered, the most suspicious looks
inet_twsk_deschedule_put vs __inet_twsk_schedule:

void inet_twsk_deschedule_put(struct inet_timewait_sock *tw)
{
        if (del_timer_sync(&tw->tw_timer))
                inet_twsk_kill(tw);
        inet_twsk_put(tw);
}

void __inet_twsk_schedule(struct inet_timewait_sock *tw, int timeo, bool rearm)
{
        tw->tw_kill = timeo <= 4*HZ;
        if (!rearm) {
                BUG_ON(mod_timer(&tw->tw_timer, jiffies + timeo));
                atomic_inc(&tw->tw_dr->tw_count);
        } else {
                mod_timer_pending(&tw->tw_timer, jiffies + timeo);
        }
}

Can't it somehow end up rearming already deleted timer? Or maybe the
first mod_timer happens after del_timer_sync?




> BUG: KASAN: use-after-free in tw_timer_handler+0xc3/0xd0
> net/ipv4/inet_timewait_sock.c:149 at addr ffff8801cb58c398
> Read of size 8 by task syz-executor0/24691
> CPU: 0 PID: 24691 Comm: syz-executor0 Not tainted 4.9.0 #3
> Hardware name: Google Google Compute Engine/Google Compute Engine,
> BIOS Google 01/01/2011
>  ffff8801dc007328 ffffffff8234530f ffffffff00000000 1ffff1003b800df8
>  ffffed003b800df0 0000000041b58ab3 ffffffff84b379b8 ffffffff82345021
>  ffff8801d8ad8f60 ffff8801d8ad8f68 ffff8801d8ad8740 000000000000002e
> Call Trace:
>  [<ffffffff819dd8fe>] __asan_report_load8_noabort+0x3e/0x40
> mm/kasan/report.c:329
>  [<ffffffff8374fd93>] tw_timer_handler+0xc3/0xd0
> net/ipv4/inet_timewait_sock.c:149
>  [<ffffffff815f5b21>] call_timer_fn+0x241/0x800 kernel/time/timer.c:1308
>  [<ffffffff815f84b7>] expire_timers kernel/time/timer.c:1348 [inline]
>  [<ffffffff815f84b7>] __run_timers+0x9e7/0xe90 kernel/time/timer.c:1641
>  [<ffffffff815f8981>] run_timer_softirq+0x21/0x80 kernel/time/timer.c:1654
>  [<ffffffff84372c7f>] __do_softirq+0x31f/0xbcd kernel/softirq.c:284
>  [<ffffffff8143c18c>] invoke_softirq kernel/softirq.c:364 [inline]
>  [<ffffffff8143c18c>] irq_exit+0x1cc/0x200 kernel/softirq.c:405
>  [<ffffffff843723ee>] exiting_irq arch/x86/include/asm/apic.h:659 [inline]
>  [<ffffffff843723ee>] smp_trace_apic_timer_interrupt+0x13e/0x6a8
> arch/x86/kernel/apic/apic.c:981
>  [<ffffffff843713dc>] trace_apic_timer_interrupt+0x8c/0xa0
> arch/x86/entry/entry_64.S:709
>  <EOI> [ 2916.083183]  [<ffffffff8436ebe6>] ? arch_local_irq_enable
> arch/x86/include/asm/paravirt.h:777 [inline]
>  <EOI> [ 2916.083183]  [<ffffffff8436ebe6>] ? __raw_spin_unlock_irq
> include/linux/spinlock_api_smp.h:170 [inline]
>  <EOI> [ 2916.083183]  [<ffffffff8436ebe6>] ?
> _raw_spin_unlock_irq+0x56/0x70 kernel/locking/spinlock.c:199
>  [<ffffffff814cbff2>] finish_lock_switch kernel/sched/sched.h:1157 [inline]
>  [<ffffffff814cbff2>] finish_task_switch+0x1c2/0x710 kernel/sched/core.c:2769
>  [<ffffffff84356654>] context_switch kernel/sched/core.c:2902 [inline]
>  [<ffffffff84356654>] __schedule+0x724/0x1e90 kernel/sched/core.c:3402
>  [<ffffffff84357ec8>] schedule+0x108/0x440 kernel/sched/core.c:3457
>  [<ffffffff8100790f>] exit_to_usermode_loop+0x20f/0x2a0
> arch/x86/entry/common.c:149
>  [<ffffffff81009413>] prepare_exit_to_usermode
> arch/x86/entry/common.c:190 [inline]
>  [<ffffffff81009413>] syscall_return_slowpath+0x4d3/0x570
> arch/x86/entry/common.c:259
>  [<ffffffff8436fa22>] entry_SYSCALL_64_fastpath+0xc0/0xc2
> Object at ffff8801cb58c1c0, in cache net_namespace size: 6656
> Allocated:
> PID = 3183
>  [ 2916.342108] [<ffffffff819dcd92>] kasan_slab_alloc+0x12/0x20
> mm/kasan/kasan.c:537
>  [ 2916.349322] [<ffffffff819d83e2>] kmem_cache_alloc+0x102/0x680 mm/slab.c:3565
>  [ 2916.356776] [<ffffffff83549a86>] kmem_cache_zalloc
> include/linux/slab.h:626 [inline]
>  [ 2916.356776] [<ffffffff83549a86>] net_alloc
> net/core/net_namespace.c:339 [inline]
>  [ 2916.356776] [<ffffffff83549a86>] copy_net_ns+0x196/0x480
> net/core/net_namespace.c:379
>  [ 2916.363783] [<ffffffff814b1349>] create_new_namespaces+0x409/0x860
> kernel/nsproxy.c:106
>  [ 2916.371605] [<ffffffff814b1aed>] copy_namespaces+0x34d/0x420
> kernel/nsproxy.c:164
>  [ 2916.379042] [<ffffffff814197f1>]
> copy_process.part.40+0x2281/0x4d30 kernel/fork.c:1659
>  [ 2916.387013] [<ffffffff8141c7e0>] copy_process kernel/fork.c:1483 [inline]
>  [ 2916.387013] [<ffffffff8141c7e0>] _do_fork+0x200/0xff0 kernel/fork.c:1937
>  [ 2916.393730] [<ffffffff8141d6a7>] SYSC_clone kernel/fork.c:2047 [inline]
>  [ 2916.393730] [<ffffffff8141d6a7>] SyS_clone+0x37/0x50 kernel/fork.c:2041
>  [ 2916.400376] [<ffffffff81009798>] do_syscall_64+0x2e8/0x930
> arch/x86/entry/common.c:280
>  [ 2916.407563] [<ffffffff8436fa49>] return_from_SYSCALL_64+0x0/0x7a
> Freed:
> PID = 15107
>  [ 2916.441170] [<ffffffff819da1b1>] __cache_free mm/slab.c:3507 [inline]
>  [ 2916.441170] [<ffffffff819da1b1>] kmem_cache_free+0x71/0x240 mm/slab.c:3767
>  [ 2916.448408] [<ffffffff83548e3e>] net_free
> net/core/net_namespace.c:355 [inline]
>  [ 2916.448408] [<ffffffff83548e3e>] net_drop_ns+0x11e/0x140
> net/core/net_namespace.c:362
>  [ 2916.455370] [<ffffffff83549652>] cleanup_net+0x7f2/0xa90
> net/core/net_namespace.c:472
>  [ 2916.462331] [<ffffffff81492960>] process_one_work+0xbd0/0x1c10
> kernel/workqueue.c:2096
>  [ 2916.469877] [<ffffffff81493bc3>] worker_thread+0x223/0x1990
> kernel/workqueue.c:2230
>  [ 2916.477155] [<ffffffff814abb33>] kthread+0x323/0x3e0 kernel/kthread.c:209
>  [ 2916.483831] [<ffffffff8436fbea>] ret_from_fork+0x2a/0x40
> arch/x86/entry/entry_64.S:433
> Memory state around the buggy address:
>  ffff8801cb58c280: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
>  ffff8801cb58c300: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
>>ffff8801cb58c380: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
>                             ^
>  ffff8801cb58c400: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
>  ffff8801cb58c480: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
> ==================================================================
>
> BUG: KASAN: use-after-free in tw_timer_handler+0xc3/0xd0
> net/ipv4/inet_timewait_sock.c:149 at addr ffff8801cd4ec298
> Read of size 8 by task swapper/1/0
> CPU: 1 PID: 0 Comm: swapper/1 Not tainted 4.9.0 #3
> Hardware name: Google Google Compute Engine/Google Compute Engine,
> BIOS Google 01/01/2011
>  ffff8801dc107468 ffffffff8234530f ffffffff00000001 1ffff1003b820e20
>  ffffed003b820e18 0000000041b58ab3 ffffffff84b379b8 ffffffff82345021
>  1ffff1003b820e17 ffff8801daf0e2c0 0000000041b58ab3 ffffffff84af4170
> Call Trace:
>  [<ffffffff819dd8fe>] __asan_report_load8_noabort+0x3e/0x40
> mm/kasan/report.c:329
>  [<ffffffff8374fd93>] tw_timer_handler+0xc3/0xd0
> net/ipv4/inet_timewait_sock.c:149
>  [<ffffffff815f5b21>] call_timer_fn+0x241/0x800 kernel/time/timer.c:1308
>  [<ffffffff815f84b7>] expire_timers kernel/time/timer.c:1348 [inline]
>  [<ffffffff815f84b7>] __run_timers+0x9e7/0xe90 kernel/time/timer.c:1641
>  [<ffffffff815f8981>] run_timer_softirq+0x21/0x80 kernel/time/timer.c:1654
>  [<ffffffff84372c7f>] __do_softirq+0x31f/0xbcd kernel/softirq.c:284
>  [<ffffffff8143c18c>] invoke_softirq kernel/softirq.c:364 [inline]
>  [<ffffffff8143c18c>] irq_exit+0x1cc/0x200 kernel/softirq.c:405
>  [<ffffffff8437228b>] exiting_irq arch/x86/include/asm/apic.h:659 [inline]
>  [<ffffffff8437228b>] smp_apic_timer_interrupt+0x7b/0xa0
> arch/x86/kernel/apic/apic.c:960
>  [<ffffffff8437133c>] apic_timer_interrupt+0x8c/0xa0
> arch/x86/entry/entry_64.S:709
>  <EOI> [ 1412.821824]  [<ffffffff8436dbb6>] ?
> native_safe_halt+0x6/0x10 arch/x86/include/asm/irqflags.h:53
>  [<ffffffff8436d08f>] arch_safe_halt
> arch/x86/include/asm/paravirt.h:103 [inline]
>  [<ffffffff8436d08f>] default_idle+0xbf/0x440 arch/x86/kernel/process.c:308
>  [<ffffffff8128a5ca>] arch_cpu_idle+0xa/0x10 arch/x86/kernel/process.c:299
>  [<ffffffff8436e0d6>] default_idle_call+0x36/0x90 kernel/sched/idle.c:96
>  [<ffffffff815549a7>] cpuidle_idle_call kernel/sched/idle.c:154 [inline]
>  [<ffffffff815549a7>] cpu_idle_loop kernel/sched/idle.c:247 [inline]
>  [<ffffffff815549a7>] cpu_startup_entry+0x327/0x4b0 kernel/sched/idle.c:302
>  [<ffffffff812e47ac>] start_secondary+0x36c/0x460 arch/x86/kernel/smpboot.c:263
> Object at ffff8801cd4ec0c0, in cache net_namespace size: 6656
> Allocated:
> PID = 3131
>  [ 1412.940699] [<ffffffff819d83e2>] kmem_cache_alloc+0x102/0x680 mm/slab.c:3565
>  [ 1412.948084] [<ffffffff83549a86>] kmem_cache_zalloc
> include/linux/slab.h:626 [inline]
>  [ 1412.948084] [<ffffffff83549a86>] net_alloc
> net/core/net_namespace.c:339 [inline]
>  [ 1412.948084] [<ffffffff83549a86>] copy_net_ns+0x196/0x480
> net/core/net_namespace.c:379
>  [ 1412.955019] [<ffffffff814b1349>] create_new_namespaces+0x409/0x860
> kernel/nsproxy.c:106
>  [ 1412.962817] [<ffffffff814b1aed>] copy_namespaces+0x34d/0x420
> kernel/nsproxy.c:164
>  [ 1412.970094] [<ffffffff814197f1>]
> copy_process.part.40+0x2281/0x4d30 kernel/fork.c:1659
>  [ 1412.978004] [<ffffffff8141c7e0>] copy_process kernel/fork.c:1483 [inline]
>  [ 1412.978004] [<ffffffff8141c7e0>] _do_fork+0x200/0xff0 kernel/fork.c:1937
>  [ 1412.984677] [<ffffffff8141d6a7>] SYSC_clone kernel/fork.c:2047 [inline]
>  [ 1412.984677] [<ffffffff8141d6a7>] SyS_clone+0x37/0x50 kernel/fork.c:2041
>  [ 1412.991276] [<ffffffff81009798>] do_syscall_64+0x2e8/0x930
> arch/x86/entry/common.c:280
>  [ 1412.998394] [<ffffffff8436fa49>] return_from_SYSCALL_64+0x0/0x7a
> Freed:
> PID = 9846
>  [ 1413.031603] [<ffffffff819da1b1>] __cache_free mm/slab.c:3507 [inline]
>  [ 1413.031603] [<ffffffff819da1b1>] kmem_cache_free+0x71/0x240 mm/slab.c:3767
>  [ 1413.038796] [<ffffffff83548e3e>] net_free
> net/core/net_namespace.c:355 [inline]
>  [ 1413.038796] [<ffffffff83548e3e>] net_drop_ns+0x11e/0x140
> net/core/net_namespace.c:362
>  [ 1413.045734] [<ffffffff83549652>] cleanup_net+0x7f2/0xa90
> net/core/net_namespace.c:472
>  [ 1413.052667] [<ffffffff81492960>] process_one_work+0xbd0/0x1c10
> kernel/workqueue.c:2096
>  [ 1413.060120] [<ffffffff81493bc3>] worker_thread+0x223/0x1990
> kernel/workqueue.c:2230
>  [ 1413.067357] [<ffffffff814abb33>] kthread+0x323/0x3e0 kernel/kthread.c:209
>  [ 1413.073944] [<ffffffff8436fbea>] ret_from_fork+0x2a/0x40
> arch/x86/entry/entry_64.S:433
> Memory state around the buggy address:
>  ffff8801cd4ec180: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
>  ffff8801cd4ec200: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
>>ffff8801cd4ec280: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
>                             ^
>  ffff8801cd4ec300: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
>  ffff8801cd4ec380: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
> ==================================================================
>
> BUG: KASAN: use-after-free in tw_timer_handler+0xc3/0xd0
> net/ipv4/inet_timewait_sock.c:149 at addr ffff8801b7b50358
> Read of size 8 by task swapper/0/0
> CPU: 0 PID: 0 Comm: swapper/0 Not tainted 4.9.0 #3
> Hardware name: Google Google Compute Engine/Google Compute Engine,
> BIOS Google 01/01/2011
>  ffff8801dc007468 ffffffff8234530f ffffffff00000000 1ffff1003b800e20
>  ffffed003b800e18 0000000041b58ab3 ffffffff84b379b8 ffffffff82345021
>  ffffffff84e2bba0 ffffffff84e2bba8 ffffffff84e2b380 000000000000002e
> Call Trace:
>  [<ffffffff819dd8fe>] __asan_report_load8_noabort+0x3e/0x40
> mm/kasan/report.c:329
>  [<ffffffff8374fd93>] tw_timer_handler+0xc3/0xd0
> net/ipv4/inet_timewait_sock.c:149
>  [<ffffffff815f5b21>] call_timer_fn+0x241/0x800 kernel/time/timer.c:1308
>  [<ffffffff815f84b7>] expire_timers kernel/time/timer.c:1348 [inline]
>  [<ffffffff815f84b7>] __run_timers+0x9e7/0xe90 kernel/time/timer.c:1641
>  [<ffffffff815f8981>] run_timer_softirq+0x21/0x80 kernel/time/timer.c:1654
>  [<ffffffff84372c7f>] __do_softirq+0x31f/0xbcd kernel/softirq.c:284
>  [<ffffffff8143c18c>] invoke_softirq kernel/softirq.c:364 [inline]
>  [<ffffffff8143c18c>] irq_exit+0x1cc/0x200 kernel/softirq.c:405
>  [<ffffffff8437228b>] exiting_irq arch/x86/include/asm/apic.h:659 [inline]
>  [<ffffffff8437228b>] smp_apic_timer_interrupt+0x7b/0xa0
> arch/x86/kernel/apic/apic.c:960
>  [<ffffffff8437133c>] apic_timer_interrupt+0x8c/0xa0
> arch/x86/entry/entry_64.S:709
>  <EOI> [ 1965.936792]  [<ffffffff8436dbb6>] ?
> native_safe_halt+0x6/0x10 arch/x86/include/asm/irqflags.h:53
>  [<ffffffff8436d08f>] arch_safe_halt
> arch/x86/include/asm/paravirt.h:103 [inline]
>  [<ffffffff8436d08f>] default_idle+0xbf/0x440 arch/x86/kernel/process.c:308
>  [<ffffffff8128a5ca>] arch_cpu_idle+0xa/0x10 arch/x86/kernel/process.c:299
>  [<ffffffff8436e0d6>] default_idle_call+0x36/0x90 kernel/sched/idle.c:96
>  [<ffffffff815549a7>] cpuidle_idle_call kernel/sched/idle.c:154 [inline]
>  [<ffffffff815549a7>] cpu_idle_loop kernel/sched/idle.c:247 [inline]
>  [<ffffffff815549a7>] cpu_startup_entry+0x327/0x4b0 kernel/sched/idle.c:302
>  [<ffffffff8434f05d>] rest_init+0x18d/0x1a0 init/main.c:408
>  [<ffffffff85481b16>] start_kernel+0x7a0/0x7d2 init/main.c:660
>  [<ffffffff854802e6>] x86_64_start_reservations+0x2a/0x2c
> arch/x86/kernel/head64.c:195
>  [<ffffffff85480424>] x86_64_start_kernel+0x13c/0x149
> arch/x86/kernel/head64.c:176
> Object at ffff8801b7b50180, in cache net_namespace size: 6656
> Allocated:
> PID = 3169
>  [ 1966.129951] [<ffffffff819d83e2>] kmem_cache_alloc+0x102/0x680 mm/slab.c:3565
>  [ 1966.137357] [<ffffffff83549a86>] kmem_cache_zalloc
> include/linux/slab.h:626 [inline]
>  [ 1966.137357] [<ffffffff83549a86>] net_alloc
> net/core/net_namespace.c:339 [inline]
>  [ 1966.137357] [<ffffffff83549a86>] copy_net_ns+0x196/0x480
> net/core/net_namespace.c:379
>  [ 1966.144350] [<ffffffff814b1349>] create_new_namespaces+0x409/0x860
> kernel/nsproxy.c:106
>  [ 1966.152254] [<ffffffff814b1aed>] copy_namespaces+0x34d/0x420
> kernel/nsproxy.c:164
>  [ 1966.159567] [<ffffffff814197f1>]
> copy_process.part.40+0x2281/0x4d30 kernel/fork.c:1659
>  [ 1966.167484] [<ffffffff8141c7e0>] copy_process kernel/fork.c:1483 [inline]
>  [ 1966.167484] [<ffffffff8141c7e0>] _do_fork+0x200/0xff0 kernel/fork.c:1937
>  [ 1966.174207] [<ffffffff8141d6a7>] SYSC_clone kernel/fork.c:2047 [inline]
>  [ 1966.174207] [<ffffffff8141d6a7>] SyS_clone+0x37/0x50 kernel/fork.c:2041
>  [ 1966.180832] [<ffffffff81009798>] do_syscall_64+0x2e8/0x930
> arch/x86/entry/common.c:280
>  [ 1966.187973] [<ffffffff8436fa49>] return_from_SYSCALL_64+0x0/0x7a
> Freed:
> PID = 8938
>  [ 1966.221347] [<ffffffff819da1b1>] __cache_free mm/slab.c:3507 [inline]
>  [ 1966.221347] [<ffffffff819da1b1>] kmem_cache_free+0x71/0x240 mm/slab.c:3767
>  [ 1966.228568] [<ffffffff83548e3e>] net_free
> net/core/net_namespace.c:355 [inline]
>  [ 1966.228568] [<ffffffff83548e3e>] net_drop_ns+0x11e/0x140
> net/core/net_namespace.c:362
>  [ 1966.235564] [<ffffffff83549652>] cleanup_net+0x7f2/0xa90
> net/core/net_namespace.c:472
>  [ 1966.242517] [<ffffffff81492960>] process_one_work+0xbd0/0x1c10
> kernel/workqueue.c:2096
>  [ 1966.249995] [<ffffffff81493bc3>] worker_thread+0x223/0x1990
> kernel/workqueue.c:2230
>  [ 1966.257258] [<ffffffff814abb33>] kthread+0x323/0x3e0 kernel/kthread.c:209
>  [ 1966.263879] [<ffffffff8436fbea>] ret_from_fork+0x2a/0x40
> arch/x86/entry/entry_64.S:433
> Memory state around the buggy address:
>  ffff8801b7b50200: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
>  ffff8801b7b50280: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
>>ffff8801b7b50300: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
>                                                     ^
>  ffff8801b7b50380: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
>  ffff8801b7b50400: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
> ==================================================================
>
> BUG: KASAN: slab-out-of-bounds in tw_timer_handler+0xc3/0xd0
> net/ipv4/inet_timewait_sock.c:149 at addr ffff8801c98f43a0
> Read of size 8 by task syz-executor8/3423
> CPU: 0 PID: 3423 Comm: syz-executor8 Not tainted 4.10.0-rc5 #19
> Hardware name: Google Google Compute Engine/Google Compute Engine,
> BIOS Google 01/01/2011
> Call Trace:
>  <IRQ>
>  __dump_stack lib/dump_stack.c:15 [inline]
>  dump_stack+0x2ee/0x3ef lib/dump_stack.c:51
>  kasan_object_err+0x1c/0x70 mm/kasan/report.c:161
>  print_address_description mm/kasan/report.c:199 [inline]
>  kasan_report_error+0x1d1/0x4d0 mm/kasan/report.c:288
>  kasan_report mm/kasan/report.c:308 [inline]
>  __asan_report_load8_noabort+0x3e/0x40 mm/kasan/report.c:329
>  tw_timer_handler+0xc3/0xd0 net/ipv4/inet_timewait_sock.c:149
>  call_timer_fn+0x241/0x820 kernel/time/timer.c:1308
>  expire_timers kernel/time/timer.c:1348 [inline]
>  __run_timers+0x9e7/0xe90 kernel/time/timer.c:1642
>  run_timer_softirq+0x21/0x80 kernel/time/timer.c:1655
>  __do_softirq+0x31f/0xbe7 kernel/softirq.c:284
>  invoke_softirq kernel/softirq.c:364 [inline]
>  irq_exit+0x1cc/0x200 kernel/softirq.c:405
>  exiting_irq arch/x86/include/asm/apic.h:658 [inline]
>  smp_apic_timer_interrupt+0x76/0xa0 arch/x86/kernel/apic/apic.c:961
>  apic_timer_interrupt+0x93/0xa0 arch/x86/entry/entry_64.S:707
> RIP: 0010:arch_local_save_flags arch/x86/include/asm/paravirt.h:762 [inline]
> RIP: 0010:arch_local_irq_save arch/x86/include/asm/paravirt.h:784 [inline]
> RIP: 0010:lock_is_held_type+0x124/0x310 kernel/locking/lockdep.c:3787
> RSP: 0018:ffff8801c946f558 EFLAGS: 00000286 ORIG_RAX: ffffffffffffff10
> RAX: 0000000000000286 RBX: 1ffff1003928deac RCX: 1ffff1003928deb0
> RDX: 1ffffffff0a18984 RSI: 00000000ffffffff RDI: ffffffff850c4c20
> RBP: ffff8801c946f6a8 R08: 0000000000000002 R09: 0000000000000001
> R10: 000000000000000a R11: 0000000000000000 R12: ffff8801c946f680
> R13: ffff8801c9492640 R14: ffffffff85130ec0 R15: 0000000000000bff
>  </IRQ>
>  lock_is_held include/linux/lockdep.h:348 [inline]
>  ___might_sleep+0x5b3/0x650 kernel/sched/core.c:7748
>  __might_sleep+0x95/0x1a0 kernel/sched/core.c:7739
>  cache_alloc_debugcheck_before mm/slab.c:3071 [inline]
>  slab_alloc mm/slab.c:3386 [inline]
>  kmem_cache_alloc+0x273/0x680 mm/slab.c:3558
>  shmem_alloc_inode+0x1b/0x40 mm/shmem.c:3647
>  alloc_inode+0x61/0x180 fs/inode.c:207
>  new_inode_pseudo+0x69/0x170 fs/inode.c:889
>  new_inode+0x1c/0x40 fs/inode.c:918
>  shmem_get_inode+0xd1/0x8a0 mm/shmem.c:2120
>  shmem_mknod+0x58/0x1b0 mm/shmem.c:2824
>  shmem_mkdir+0x29/0x50 mm/shmem.c:2875
>  vfs_mkdir+0x3be/0x600 fs/namei.c:3738
>  SYSC_mkdirat fs/namei.c:3761 [inline]
>  SyS_mkdirat fs/namei.c:3745 [inline]
>  SYSC_mkdir fs/namei.c:3772 [inline]
>  SyS_mkdir+0x16e/0x290 fs/namei.c:3770
>  entry_SYSCALL_64_fastpath+0x1f/0xc2
> RIP: 0033:0x44ec87
> RSP: 002b:0000000001a2fe40 EFLAGS: 00000212 ORIG_RAX: 0000000000000053
> RAX: ffffffffffffffda RBX: 0000000000000010 RCX: 000000000044ec87
> RDX: 0000000001a2fe6e RSI: 00000000000001ff RDI: 0000000001a2fe68
> RBP: 00000000000019ec R08: 0000000000000000 R09: 0000000000000006
> R10: 0000000000000064 R11: 0000000000000212 R12: 0000000001ef390c
> R13: 0000000000000000 R14: 00000000000a43b5 R15: 00000000000019ec
> Object at ffff8801c98f44c0, in cache task_struct size: 5696
> Allocated:
> PID = 3452
> [<ffffffff8129f656>] save_stack_trace+0x16/0x20 arch/x86/kernel/stacktrace.c:57
> [<ffffffff819f6f53>] save_stack+0x43/0xd0 mm/kasan/kasan.c:502
> [<ffffffff819f71da>] set_track mm/kasan/kasan.c:514 [inline]
> [<ffffffff819f71da>] kasan_kmalloc+0xaa/0xd0 mm/kasan/kasan.c:605
> [<ffffffff819f77d2>] kasan_slab_alloc+0x12/0x20 mm/kasan/kasan.c:544
> [<ffffffff819f1652>] kmem_cache_alloc_node+0x122/0x690 mm/slab.c:3650
> [<ffffffff81421fe2>] alloc_task_struct_node kernel/fork.c:142 [inline]
> [<ffffffff81421fe2>] dup_task_struct kernel/fork.c:482 [inline]
> [<ffffffff81421fe2>] copy_process.part.42+0x1a32/0x5fd0 kernel/fork.c:1515
> [<ffffffff81426ac0>] copy_process kernel/fork.c:1486 [inline]
> [<ffffffff81426ac0>] _do_fork+0x200/0xff0 kernel/fork.c:1942
> [<ffffffff81427987>] SYSC_clone kernel/fork.c:2052 [inline]
> [<ffffffff81427987>] SyS_clone+0x37/0x50 kernel/fork.c:2046
> [<ffffffff81009798>] do_syscall_64+0x2e8/0x930 arch/x86/entry/common.c:280
> [<ffffffff8440fb09>] return_from_SYSCALL_64+0x0/0x7a
> Freed:
> PID = 29885
> [<ffffffff8129f656>] save_stack_trace+0x16/0x20 arch/x86/kernel/stacktrace.c:57
> [<ffffffff819f6f53>] save_stack+0x43/0xd0 mm/kasan/kasan.c:502
> [<ffffffff819f784f>] set_track mm/kasan/kasan.c:514 [inline]
> [<ffffffff819f784f>] kasan_slab_free+0x6f/0xb0 mm/kasan/kasan.c:578
> [<ffffffff819f4bf1>] __cache_free mm/slab.c:3502 [inline]
> [<ffffffff819f4bf1>] kmem_cache_free+0x71/0x240 mm/slab.c:3762
> [<ffffffff8141f041>] free_task_struct kernel/fork.c:147 [inline]
> [<ffffffff8141f041>] free_task+0x151/0x1d0 kernel/fork.c:359
> [<ffffffff8141f30b>] __put_task_struct+0x24b/0x5f0 kernel/fork.c:396
> [<ffffffff81435baa>] put_task_struct include/linux/sched.h:2257 [inline]
> [<ffffffff81435baa>] delayed_put_task_struct+0xca/0x3f0 kernel/exit.c:173
> [<ffffffff815ef250>] __rcu_reclaim kernel/rcu/rcu.h:118 [inline]
> [<ffffffff815ef250>] rcu_do_batch.isra.70+0x9e0/0xdf0 kernel/rcu/tree.c:2780
> [<ffffffff815efad2>] invoke_rcu_callbacks kernel/rcu/tree.c:3043 [inline]
> [<ffffffff815efad2>] __rcu_process_callbacks kernel/rcu/tree.c:3010 [inline]
> [<ffffffff815efad2>] rcu_process_callbacks+0x472/0xc70 kernel/rcu/tree.c:3027
> [<ffffffff84412d7f>] __do_softirq+0x31f/0xbe7 kernel/softirq.c:284
> Memory state around the buggy address:
>  ffff8801c98f4280: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
>  ffff8801c98f4300: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
>>ffff8801c98f4380: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
>                                ^
>  ffff8801c98f4400: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
>  ffff8801c98f4480: fc fc fc fc fc fc fc fc fb fb fb fb fb fb fb fb
> ==================================================================

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