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SubjectRe: WARNING in refcount_sub_and_test
Maybe I have just made some mistakes on understanding the reproduction
methods, will try it again.

Thanks,
- ChunYu

On Thu, Oct 26, 2017 at 10:49 PM, Dmitry Vyukov <dvyukov@google.com> wrote:
> On Thu, Oct 26, 2017 at 10:53 AM, ChunYu Wang <chunwang@redhat.com> wrote:
>> Hi all,
>>
>> I am failed to reproduce it on target kernel with the reproducer file
>> or replaying the target syzkaller description log file, do I made
>> something wrong or there exists more subjects then the line in
>> repro.txt:
>>
>> #{Threaded:true Collide:true Repeat:false Procs:1 Sandbox:namespace
>> Fault:false FaultCall:-1 FaultNth:0 EnableTun:false UseTmpDir:true
>> HandleSegv:false WaitRepeat:false Debug:false Repro:false}
>
>
> Hi ChunYu,
>
> I've just re-tested the C repro and was able to trigger the bug in a second.
> I've checked out 49ca1943a7adb429b11b8e05d81bc821694b76c7, copied the
> provided config, run make olddefconfig, built with gcc-7 (you can get
> the exact one here
> https://storage.googleapis.com/syzkaller/gcc-7.tar.gz). Then run in
> qemu (most of the flags are probably irrelevant):
>
> qemu-system-x86_64 -hda wheezy.img -net
> user,host=10.0.2.10,hostfwd=tcp::10022-:22 -net nic -nographic -kernel
> arch/x86/boot/bzImage -append "kvm-intel.nested=1
> kvm-intel.unrestricted_guest=1 kvm-intel.ept=1
> kvm-intel.flexpriority=1 kvm-intel.vpid=1
> kvm-intel.emulate_invalid_guest_state=1 kvm-intel.eptad=1
> kvm-intel.enable_shadow_vmcs=1 kvm-intel.pml=1
> kvm-intel.enable_apicv=1 console=ttyS0 root=/dev/sda
> earlyprintk=serial slub_debug=UZ vsyscall=native rodata=n oops=panic
> panic_on_warn=1 panic=86400" -enable-kvm -pidfile vm_pid -m 2G -smp 4
> -cpu host -usb -usbdevice mouse -usbdevice tablet -soundhw all
>
> And running the provided C program instantly spewed the following.
>
> Is there anything you did differently? I would like to understand
> common reasons why syzbot reproducers don't work and outline them
> here:
> https://github.com/google/syzkaller/blob/master/docs/syzbot.md
>
> Thanks
>
>
> [ 588.444300] refcount_t: underflow; use-after-free.
> [ 588.445812] ------------[ cut here ]------------
> [ 588.447026] WARNING: CPU: 1 PID: 3086 at lib/refcount.c:186
> refcount_sub_and_test+0x167/0x1b0
> [ 588.449082] Kernel panic - not syncing: panic_on_warn set ...
> [ 588.449082]
> [ 588.450737] CPU: 1 PID: 3086 Comm: a.out Not tainted 4.14.0-rc5+ #9
> [ 588.452160] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996),
> BIOS Bochs 01/01/2011
> [ 588.454059] Call Trace:
> [ 588.454658] dump_stack+0x194/0x257
> [ 588.455538] ? arch_local_irq_restore+0x53/0x53
> [ 588.456630] panic+0x1e4/0x417
> [ 588.457367] ? __warn+0x1d9/0x1d9
> [ 588.458171] ? show_regs_print_info+0x65/0x65
> [ 588.459234] ? refcount_sub_and_test+0x167/0x1b0
> [ 588.460262] __warn+0x1c4/0x1d9
> [ 588.460958] ? refcount_sub_and_test+0x167/0x1b0
> [ 588.461965] report_bug+0x211/0x2d0
> [ 588.462756] fixup_bug+0x40/0x90
> [ 588.463597] do_trap+0x260/0x390
> [ 588.464304] do_error_trap+0x120/0x390
> [ 588.465105] ? vprintk_emit+0x49b/0x590
> [ 588.465929] ? do_trap+0x390/0x390
> [ 588.466661] ? refcount_sub_and_test+0x167/0x1b0
> [ 588.467646] ? vprintk_emit+0x3ea/0x590
> [ 588.468475] ? trace_hardirqs_off_thunk+0x1a/0x1c
> [ 588.469482] do_invalid_op+0x1b/0x20
> [ 588.470262] invalid_op+0x18/0x20
> [ 588.470988] RIP: 0010:refcount_sub_and_test+0x167/0x1b0
> [ 588.472080] RSP: 0018:ffff88006550e9c8 EFLAGS: 00010282
> [ 588.473224] RAX: 0000000000000026 RBX: 0000000000000001 RCX: 0000000000000000
> [ 588.474643] RDX: 0000000000000026 RSI: 1ffff1000caa1cf9 RDI: ffffed000caa1d2d
> [ 588.476091] RBP: ffff88006550ea58 R08: 0000000000000000 R09: 1ffff1000caa1ccb
> [ 588.477520] R10: ffff88006550e7f8 R11: ffffffff85b2cb78 R12: 1ffff1000caa1d3a
> [ 588.478967] R13: 00000000ffffff01 R14: 0000000000000100 R15: ffff88006a7f4a7c
> [ 588.480413] ? refcount_sub_and_test+0x167/0x1b0
> [ 588.481337] ? refcount_inc+0x50/0x50
> [ 588.482081] ? __sctp_outq_teardown+0xa5b/0x1230
> [ 588.483004] ? sctp_association_free+0x2d0/0x930
> [ 588.484291] ? sctp_do_sm+0x271b/0x6a30
> [ 588.485247] ? sctp_primitive_SHUTDOWN+0xa0/0xd0
> [ 588.486295] ? sctp_close+0x3c6/0x980
> [ 588.487058] ? inet_release+0xed/0x1c0
> [ 588.488370] ? sock_release+0x8d/0x1e0
> [ 588.489080] ? sock_close+0x16/0x20
> [ 588.489759] sctp_wfree+0x183/0x620
> [ 588.490430] ? entry_SYSCALL_64_fastpath+0xbc/0xbe
> [ 588.491323] ? __sctp_write_space+0x910/0x910
> [ 588.492177] skb_release_head_state+0x124/0x200
> [ 588.493078] skb_release_all+0x15/0x60
> [ 588.493938] consume_skb+0x153/0x490
> [ 588.494605] ? sctp_chunk_put+0x99/0x420
> [ 588.495388] ? alloc_skb_with_frags+0x750/0x750
> [ 588.496119] ? sctp_chunk_hold+0x20/0x20
> [ 588.496757] ? sctp_sched_dequeue_common+0x2aa/0x5d0
> [ 588.497554] ? refcount_sub_and_test+0x115/0x1b0
> [ 588.498296] ? refcount_inc+0x50/0x50
> [ 588.498888] ? trace_hardirqs_off+0xd/0x10
> [ 588.499567] ? quarantine_put+0xeb/0x190
> [ 588.500215] sctp_chunk_put+0x29c/0x420
> [ 588.500836] ? sctp_chunk_hold+0x20/0x20
> [ 588.501491] ? sctp_transport_dst_confirm+0x50/0x50
> [ 588.502266] ? sctp_sched_fcfs_dequeue+0x198/0x290
> [ 588.503027] ? sctp_sched_dequeue_common+0x5d0/0x5d0
> [ 588.504001] sctp_chunk_free+0x53/0x60
> [ 588.504692] __sctp_outq_teardown+0xa5b/0x1230
> [ 588.505493] ? sctp_inq_set_th_handler+0x1b0/0x1b0
> [ 588.506322] ? debug_check_no_locks_freed+0x3c0/0x3c0
> [ 588.507264] ? debug_check_no_locks_freed+0x3c0/0x3c0
> [ 588.508089] ? check_preempt_wakeup+0x1320/0x1320
> [ 588.508804] ? debug_check_no_locks_freed+0x3c0/0x3c0
> [ 588.509632] ? default_wake_function+0x30/0x50
> [ 588.510368] ? autoremove_wake_function+0x78/0x350
> [ 588.511101] ? lock_acquire+0x1d5/0x580
> [ 588.511686] ? lock_acquire+0x1d5/0x580
> [ 588.512299] ? finish_wait+0x490/0x490
> [ 588.512888] ? lock_acquire+0x1d5/0x580
> [ 588.513583] ? lock_acquire+0x1d5/0x580
> [ 588.514178] ? lock_acquire+0x1d5/0x580
> [ 588.514774] ? __wake_up_common_lock+0x1c2/0x310
> [ 588.515526] ? lock_acquire+0x1d5/0x580
> [ 588.516121] ? sock_def_wakeup+0x1f9/0x350
> [ 588.516752] ? lock_downgrade+0x990/0x990
> [ 588.517385] ? lock_release+0xa40/0xa40
> [ 588.517982] ? trace_raw_output_tick_stop+0x130/0x130
> [ 588.518766] sctp_outq_free+0x15/0x20
> [ 588.519391] sctp_association_free+0x2d0/0x930
> [ 588.520136] ? sctp_asconf_queue_teardown+0x700/0x700
> [ 588.521000] ? sock_def_wakeup+0x222/0x350
> [ 588.521702] ? sk_dst_check+0x560/0x560
> [ 588.522387] ? bpf_prog_kallsyms_find+0xbd/0x440
> [ 588.523228] sctp_do_sm+0x271b/0x6a30
> [ 588.523880] ? sctp_do_8_2_transport_strike.isra.16+0x8a0/0x8a0
> [ 588.524728] ? do_raw_spin_trylock+0x190/0x190
> [ 588.525378] ? SyS_setgroups+0x250/0x250
> [ 588.525951] ? debug_check_no_locks_freed+0x3c0/0x3c0
> [ 588.526690] ? debug_check_no_locks_freed+0x3c0/0x3c0
> [ 588.527857] ? lock_acquire+0x1d5/0x580
> [ 588.528737] ? lock_acquire+0x1d5/0x580
> [ 588.529615] ? skb_dequeue+0x12a/0x180
> [ 588.530476] ? lock_downgrade+0x990/0x990
> [ 588.531445] ? do_raw_spin_trylock+0x190/0x190
> [ 588.532466] ? lock_release+0xa40/0xa40
> [ 588.533432] ? trace_hardirqs_on+0xd/0x10
> [ 588.534373] sctp_primitive_SHUTDOWN+0xa0/0xd0
> [ 588.535412] sctp_close+0x3c6/0x980
> [ 588.536208] ? sctp_apply_peer_addr_params+0xf30/0xf30
> [ 588.537322] ? debug_check_no_locks_freed+0x3c0/0x3c0
> [ 588.538409] ? lock_acquire+0x1d5/0x580
> [ 588.539262] ? locks_remove_file+0x3fa/0x5a0
> [ 588.540192] ? cmp_ex_search+0x76/0xa0
> [ 588.541006] ? fcntl_setlk+0x10c0/0x10c0
> [ 588.541858] ? bsearch+0x83/0xa0
> [ 588.542563] ? __fsnotify_parent+0xb4/0x3a0
> [ 588.543572] ? ip_mc_drop_socket+0x1ce/0x230
> [ 588.544336] inet_release+0xed/0x1c0
> [ 588.544975] sock_release+0x8d/0x1e0
> [ 588.545618] ? sock_release+0x1e0/0x1e0
> [ 588.546300] sock_close+0x16/0x20
> [ 588.546908] __fput+0x327/0x7e0
> [ 588.547495] ? fput+0x140/0x140
> [ 588.548067] ? __bad_area_nosemaphore+0x1f4/0x3e0
> [ 588.548897] ____fput+0x15/0x20
> [ 588.549461] task_work_run+0x199/0x270
> [ 588.550127] ? task_work_cancel+0x210/0x210
> [ 588.550859] ? __do_page_fault+0x3d6/0xd60
> [ 588.551602] get_signal+0x1343/0x16d0
> [ 588.552253] ? mm_fault_error+0x2c0/0x2c0
> [ 588.552964] ? ptrace_notify+0x130/0x130
> [ 588.553746] ? __do_page_fault+0xd60/0xd60
> [ 588.554473] ? do_page_fault+0xee/0x720
> [ 588.555168] ? lock_downgrade+0x990/0x990
> [ 588.555896] ? __do_page_fault+0xd60/0xd60
> [ 588.556634] ? do_raw_spin_trylock+0x190/0x190
> [ 588.557411] ? lock_acquire+0x1d5/0x580
> [ 588.558091] ? lock_acquire+0x1d5/0x580
> [ 588.558777] do_signal+0x94/0x1ee0
> [ 588.559400] ? lock_acquire+0x1d5/0x580
> [ 588.560070] ? lock_acquire+0x1d5/0x580
> [ 588.560721] ? put_unused_fd+0x62/0x70
> [ 588.561360] ? lock_downgrade+0x990/0x990
> [ 588.562044] ? setup_sigcontext+0x7d0/0x7d0
> [ 588.562755] ? do_raw_spin_trylock+0x190/0x190
> [ 588.563526] ? task_work_add+0x10e/0x1b0
> [ 588.564254] ? __put_unused_fd+0x183/0x250
> [ 588.564943] ? alloc_fdtable+0x280/0x280
> [ 588.565605] ? cpumask_weight.constprop.3+0x45/0x45
> [ 588.566421] ? _copy_to_user+0xa2/0xc0
> [ 588.567081] ? _raw_spin_unlock+0x22/0x30
> [ 588.567755] ? fput+0xd2/0x140
> [ 588.568273] ? SYSC_accept4+0x4ec/0x850
> [ 588.568915] ? kernel_accept+0x2f0/0x2f0
> [ 588.569575] exit_to_usermode_loop+0x214/0x310
> [ 588.570318] ? trace_event_raw_event_sys_exit+0x260/0x260
> [ 588.571219] ? __do_page_fault+0xd60/0xd60
> [ 588.571911] syscall_return_slowpath+0x42f/0x510
> [ 588.572675] ? finish_task_switch+0x1aa/0x740
> [ 588.573397] ? prepare_exit_to_usermode+0x2d0/0x2d0
> [ 588.574297] ? prepare_exit_to_usermode+0x1a0/0x2d0
> [ 588.575119] ? perf_trace_sys_enter+0xc20/0xc20
> [ 588.575883] ? trace_hardirqs_on_thunk+0x1a/0x1c
> [ 588.576656] entry_SYSCALL_64_fastpath+0xbc/0xbe
> [ 588.577445] RIP: 0033:0x44cfe9
> [ 588.577963] RSP: 002b:00007ff97ff43db8 EFLAGS: 00000293 ORIG_RAX:
> 0000000000000120
> [ 588.579224] RAX: fffffffffffffff2 RBX: 0000000000000000 RCX: 000000000044cfe9
> [ 588.580397] RDX: 0000000020137ffc RSI: 0000000020b53ff0 RDI: 0000000000000003
> [ 588.581557] RBP: 00007ff97ff43dd0 R08: 00007ff97ff44700 R09: 0000000000000000
> [ 588.582718] R10: 0000000000080000 R11: 0000000000000293 R12: 0000000000000000
> [ 588.583964] R13: 0000000000000000 R14: 00007ff97ff449c0 R15: 00007ff97ff44700
> [ 588.585673] Kernel Offset: disabled
> [ 588.586263] Rebooting in 86400 seconds..

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