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SubjectKASAN: use-after-free Read in snd_timer_process_callbacks
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Hello,

syzbot found the following crash on:

HEAD commit: ac5b84a1 Add linux-next specific files for 20190408
git tree: linux-next
console output: https://syzkaller.appspot.com/x/log.txt?x=10ae80b7200000
kernel config: https://syzkaller.appspot.com/x/.config?x=42a33a21877c9c95
dashboard link: https://syzkaller.appspot.com/bug?extid=58813d77154713f4de15
compiler: gcc (GCC) 9.0.0 20181231 (experimental)
syz repro: https://syzkaller.appspot.com/x/repro.syz?x=102b9f5d200000

The bug was bisected to:

commit a7588c896b05444929ecb3d0115481988720abf6
Author: Takashi Iwai <tiwai@suse.de>
Date: Wed Mar 27 15:56:08 2019 +0000

ALSA: timer: Check ack_list emptiness instead of bit flag

bisection log: https://syzkaller.appspot.com/x/bisect.txt?x=1100d3ab200000
final crash: https://syzkaller.appspot.com/x/report.txt?x=1300d3ab200000
console output: https://syzkaller.appspot.com/x/log.txt?x=1500d3ab200000

IMPORTANT: if you fix the bug, please add the following tag to the commit:
Reported-by: syzbot+58813d77154713f4de15@syzkaller.appspotmail.com
Fixes: a7588c896b05 ("ALSA: timer: Check ack_list emptiness instead of bit
flag")

==================================================================
BUG: KASAN: use-after-free in __list_del_entry_valid+0xd2/0xf5
lib/list_debug.c:42
Read of size 8 at addr ffff8880a497a7a0 by task swapper/1/0

CPU: 1 PID: 0 Comm: swapper/1 Not tainted 5.1.0-rc3-next-20190408 #20
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS
Google 01/01/2011
Call Trace:
<IRQ>
__dump_stack lib/dump_stack.c:77 [inline]
dump_stack+0x172/0x1f0 lib/dump_stack.c:113
print_address_description.cold+0x7c/0x20d mm/kasan/report.c:187
kasan_report.cold+0x1b/0x40 mm/kasan/report.c:317
__asan_report_load8_noabort+0x14/0x20 mm/kasan/generic_report.c:132
__list_del_entry_valid+0xd2/0xf5 lib/list_debug.c:42
__list_del_entry include/linux/list.h:117 [inline]
list_del_init include/linux/list.h:176 [inline]
snd_timer_process_callbacks+0x7f/0x2f0 sound/core/timer.c:763
snd_timer_interrupt sound/core/timer.c:883 [inline]
snd_timer_interrupt+0x578/0xdd0 sound/core/timer.c:804
snd_hrtimer_callback+0x219/0x3e0 sound/core/hrtimer.c:64
__run_hrtimer kernel/time/hrtimer.c:1389 [inline]
__hrtimer_run_queues+0x33e/0xde0 kernel/time/hrtimer.c:1451
hrtimer_interrupt+0x314/0x770 kernel/time/hrtimer.c:1509
local_apic_timer_interrupt arch/x86/kernel/apic/apic.c:1035 [inline]
smp_apic_timer_interrupt+0x120/0x570 arch/x86/kernel/apic/apic.c:1060
apic_timer_interrupt+0xf/0x20 arch/x86/entry/entry_64.S:807
RIP: 0010:arch_local_irq_restore arch/x86/include/asm/paravirt.h:767
[inline]
RIP: 0010:__raw_spin_unlock_irqrestore include/linux/spinlock_api_smp.h:160
[inline]
RIP: 0010:_raw_spin_unlock_irqrestore+0x95/0xe0
kernel/locking/spinlock.c:184
Code: 48 c7 c0 70 9b 92 88 48 ba 00 00 00 00 00 fc ff df 48 c1 e8 03 80 3c
10 00 75 39 48 83 3d 22 d5 78 01 00 74 24 48 89 df 57 9d <0f> 1f 44 00 00
bf 01 00 00 00 e8 dc e1 33 fa 65 8b 05 25 27 e8 78
RSP: 0018:ffff8880ae907920 EFLAGS: 00000282 ORIG_RAX: ffffffffffffff13
RAX: 1ffffffff112536e RBX: 0000000000000282 RCX: 0000000000000000
RDX: dffffc0000000000 RSI: ffff8880aa292bc0 RDI: 0000000000000282
RBP: ffff8880ae907930 R08: ffff8880aa292340 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000000 R12: ffff888097bafab8
R13: ffff8880aa20bb00 R14: ffff888097baf8b0 R15: 0000000000000001
spin_unlock_irqrestore include/linux/spinlock.h:384 [inline]
test_clear_page_writeback+0x397/0x13b0 mm/page-writeback.c:2741
end_page_writeback+0x22a/0x4f0 mm/filemap.c:1311
ext4_finish_bio+0x63e/0xb10 fs/ext4/page-io.c:119
ext4_end_bio+0x190/0x6a0 fs/ext4/page-io.c:343
bio_endio+0x5f8/0xad0 block/bio.c:1879
req_bio_endio block/blk-core.c:196 [inline]
blk_update_request+0x317/0xba0 block/blk-core.c:1457
scsi_end_request+0x7f/0x860 drivers/scsi/scsi_lib.c:579
scsi_io_completion+0x20a/0x1420 drivers/scsi/scsi_lib.c:964
scsi_finish_command+0x3ba/0x670 drivers/scsi/scsi.c:219
scsi_softirq_done+0x33b/0x3e0 drivers/scsi/scsi_lib.c:1464
blk_done_softirq+0x304/0x4d0 block/blk-softirq.c:37
__do_softirq+0x266/0x95a kernel/softirq.c:293
invoke_softirq kernel/softirq.c:374 [inline]
irq_exit+0x180/0x1d0 kernel/softirq.c:414
exiting_irq arch/x86/include/asm/apic.h:536 [inline]
do_IRQ+0x114/0x1d0 arch/x86/kernel/irq.c:258
common_interrupt+0xf/0xf arch/x86/entry/entry_64.S:583
</IRQ>
RIP: 0010:native_safe_halt+0x2/0x10 arch/x86/include/asm/irqflags.h:58
Code: ff ff ff 48 89 c7 48 89 45 d8 e8 c9 80 8f fa 48 8b 45 d8 e9 ce fe ff
ff 48 89 df e8 b8 80 8f fa eb 82 90 90 90 90 90 90 fb f4 <c3> 0f 1f 00 66
2e 0f 1f 84 00 00 00 00 00 f4 c3 90 90 90 90 90 90
RSP: 0018:ffff8880aa2a7d78 EFLAGS: 00000282 ORIG_RAX: ffffffffffffffdd
RAX: 1ffffffff1125371 RBX: ffff8880aa292340 RCX: 0000000000000000
RDX: dffffc0000000000 RSI: 0000000000000006 RDI: ffff8880aa292bbc
RBP: ffff8880aa2a7da8 R08: ffff8880aa292340 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000000 R12: 0000000000000001
R13: ffffffff88929b78 R14: 0000000000000001 R15: 0000000000000000
arch_cpu_idle+0x10/0x20 arch/x86/kernel/process.c:567
default_idle_call+0x36/0x90 kernel/sched/idle.c:93
cpuidle_idle_call kernel/sched/idle.c:153 [inline]
do_idle+0x386/0x570 kernel/sched/idle.c:262
cpu_startup_entry+0x1b/0x20 kernel/sched/idle.c:353
start_secondary+0x360/0x4d0 arch/x86/kernel/smpboot.c:267
secondary_startup_64+0xa4/0xb0 arch/x86/kernel/head_64.S:243

Allocated by task 7668:
save_stack+0x45/0xd0 mm/kasan/common.c:75
set_track mm/kasan/common.c:87 [inline]
__kasan_kmalloc mm/kasan/common.c:497 [inline]
__kasan_kmalloc.constprop.0+0xcf/0xe0 mm/kasan/common.c:470
kasan_kmalloc+0x9/0x10 mm/kasan/common.c:511
kmem_cache_alloc_trace+0x151/0x760 mm/slab.c:3621
kmalloc include/linux/slab.h:547 [inline]
kzalloc include/linux/slab.h:742 [inline]
snd_timer_instance_new+0x4f/0x3d0 sound/core/timer.c:109
snd_timer_open+0x8a7/0x1760 sound/core/timer.c:313
snd_seq_timer_open+0x240/0x590 sound/core/seq/seq_timer.c:290
queue_use+0xcb/0x240 sound/core/seq/seq_queue.c:502
snd_seq_queue_alloc+0x2c5/0x4d0 sound/core/seq/seq_queue.c:189
snd_seq_ioctl_create_queue+0xb0/0x330 sound/core/seq/seq_clientmgr.c:1522
snd_seq_ioctl+0x224/0x3e0 sound/core/seq/seq_clientmgr.c:2138
vfs_ioctl fs/ioctl.c:46 [inline]
file_ioctl fs/ioctl.c:509 [inline]
do_vfs_ioctl+0xd6e/0x1390 fs/ioctl.c:696
ksys_ioctl+0xab/0xd0 fs/ioctl.c:713
__do_sys_ioctl fs/ioctl.c:720 [inline]
__se_sys_ioctl fs/ioctl.c:718 [inline]
__x64_sys_ioctl+0x73/0xb0 fs/ioctl.c:718
do_syscall_64+0x103/0x610 arch/x86/entry/common.c:290
entry_SYSCALL_64_after_hwframe+0x49/0xbe

Freed by task 7668:
save_stack+0x45/0xd0 mm/kasan/common.c:75
set_track mm/kasan/common.c:87 [inline]
__kasan_slab_free+0x102/0x150 mm/kasan/common.c:459
kasan_slab_free+0xe/0x10 mm/kasan/common.c:467
__cache_free mm/slab.c:3498 [inline]
kfree+0xcf/0x230 mm/slab.c:3821
snd_timer_close_locked+0x6fd/0xd60 sound/core/timer.c:405
snd_timer_close+0x2e/0x70 sound/core/timer.c:430
snd_seq_timer_close+0x91/0xd0 sound/core/seq/seq_timer.c:329
queue_delete+0x52/0xb0 sound/core/seq/seq_queue.c:147
snd_seq_queue_client_leave+0x36/0x170 sound/core/seq/seq_queue.c:584
seq_free_client1.part.0+0xf3/0x270 sound/core/seq/seq_clientmgr.c:263
seq_free_client1 sound/core/seq/seq_clientmgr.c:256 [inline]
seq_free_client+0x80/0xf0 sound/core/seq/seq_clientmgr.c:285
snd_seq_release+0x55/0xf0 sound/core/seq/seq_clientmgr.c:366
__fput+0x2e5/0x8d0 fs/file_table.c:278
____fput+0x16/0x20 fs/file_table.c:309
task_work_run+0x14a/0x1c0 kernel/task_work.c:113
get_signal+0x1961/0x1d50 kernel/signal.c:2391
do_signal+0x87/0x1940 arch/x86/kernel/signal.c:816
exit_to_usermode_loop+0x244/0x2c0 arch/x86/entry/common.c:162
prepare_exit_to_usermode arch/x86/entry/common.c:197 [inline]
syscall_return_slowpath arch/x86/entry/common.c:268 [inline]
do_syscall_64+0x52d/0x610 arch/x86/entry/common.c:293
entry_SYSCALL_64_after_hwframe+0x49/0xbe

The buggy address belongs to the object at ffff8880a497a700
which belongs to the cache kmalloc-256 of size 256
The buggy address is located 160 bytes inside of
256-byte region [ffff8880a497a700, ffff8880a497a800)
The buggy address belongs to the page:
page:ffffea0002925e80 count:1 mapcount:0 mapping:ffff88812c3f07c0
index:0xffff8880a497a200
flags: 0x1fffc0000000200(slab)
raw: 01fffc0000000200 ffff88812c3f1638 ffff88812c3f1638 ffff88812c3f07c0
raw: ffff8880a497a200 ffff8880a497a0c0 000000010000000b 0000000000000000
page dumped because: kasan: bad access detected

Memory state around the buggy address:
ffff8880a497a680: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
ffff8880a497a700: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
> ffff8880a497a780: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
^
ffff8880a497a800: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
ffff8880a497a880: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
==================================================================


---
This bug is generated by a bot. It may contain errors.
See https://goo.gl/tpsmEJ for more information about syzbot.
syzbot engineers can be reached at syzkaller@googlegroups.com.

syzbot will keep track of this bug report. See:
https://goo.gl/tpsmEJ#status for how to communicate with syzbot.
For information about bisection process see: https://goo.gl/tpsmEJ#bisection
syzbot can test patches for this bug, for details see:
https://goo.gl/tpsmEJ#testing-patches

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