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SubjectKASAN: alloca-out-of-bounds Read in unwind_next_frame

syzbot hit the following crash on upstream commit
06dd3dfeea60e2a6457a6aedf97afc8e6d2ba497 (Thu Apr 5 03:07:20 2018 +0000)
Merge tag 'char-misc-4.17-rc1' of
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syzkaller reproducer:
Raw console output:
Kernel config:
compiler: gcc (GCC) 8.0.1 20180301 (experimental)

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BUG: KASAN: alloca-out-of-bounds in __read_once_size
include/linux/compiler.h:188 [inline]
BUG: KASAN: alloca-out-of-bounds in unwind_next_frame.part.7+0x7ce/0x9c0
Read of size 8 at addr ffff8801b05e67f8 by task syz-executor2/11326

CPU: 0 PID: 11326 Comm: syz-executor2 Not tainted 4.16.0+ #1
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS
Google 01/01/2011
Call Trace:
__dump_stack lib/dump_stack.c:17 [inline]
dump_stack+0x1b9/0x29f lib/dump_stack.c:53
print_address_description+0x6c/0x20b mm/kasan/report.c:256
kasan_report_error mm/kasan/report.c:354 [inline]
kasan_report.cold.7+0xac/0x2f5 mm/kasan/report.c:412
__asan_report_load8_noabort+0x14/0x20 mm/kasan/report.c:433
__read_once_size include/linux/compiler.h:188 [inline]
unwind_next_frame.part.7+0x7ce/0x9c0 arch/x86/kernel/unwind_frame.c:326
unwind_next_frame+0x3e/0x50 arch/x86/kernel/unwind_frame.c:287
__save_stack_trace+0x6e/0xd0 arch/x86/kernel/stacktrace.c:44
save_stack_trace+0x1a/0x20 arch/x86/kernel/stacktrace.c:60
save_stack+0x43/0xd0 mm/kasan/kasan.c:447
set_track mm/kasan/kasan.c:459 [inline]
__kasan_slab_free+0x11a/0x170 mm/kasan/kasan.c:520
kasan_slab_free+0xe/0x10 mm/kasan/kasan.c:527
__cache_free mm/slab.c:3486 [inline]
kmem_cache_free+0x86/0x2d0 mm/slab.c:3744
__d_free+0x20/0x30 fs/dcache.c:257
__rcu_reclaim kernel/rcu/rcu.h:178 [inline]
rcu_do_batch kernel/rcu/tree.c:2675 [inline]
invoke_rcu_callbacks kernel/rcu/tree.c:2930 [inline]
__rcu_process_callbacks kernel/rcu/tree.c:2897 [inline]
rcu_process_callbacks+0x941/0x15f0 kernel/rcu/tree.c:2914
__do_softirq+0x2e0/0xaf5 kernel/softirq.c:285
invoke_softirq kernel/softirq.c:365 [inline]
irq_exit+0x1d1/0x200 kernel/softirq.c:405
exiting_irq arch/x86/include/asm/apic.h:525 [inline]
smp_apic_timer_interrupt+0x17e/0x710 arch/x86/kernel/apic/apic.c:1052
apic_timer_interrupt+0xf/0x20 arch/x86/entry/entry_64.S:862
RIP: 0010:kasan_unpoison_shadow+0x1/0x50 mm/kasan/kasan.c:68
RSP: 0018:ffff8801b05e67e8 EFLAGS: 00000202 ORIG_RAX: ffffffffffffff13
RAX: ffff8801c1b24100 RBX: 0000000000000000 RCX: ffffffff859d4219
RDX: 0000000000000000 RSI: 00000000000000a8 RDI: ffff8801b05e6760
RBP: ffff8801b05e67f8 R08: ffff8801c1b24100 R09: ffffed003b6046c2
R10: ffffed003b6046c2 R11: ffff8801db023613 R12: 0000000000000015
R13: 0000000000000001 R14: 0000000000000016 R15: dffffc0000000000
constrain_params_by_rules+0xbaa/0x1410 sound/core/pcm_param_trace.h:28
snd_pcm_hw_refine+0x8e9/0x1180 sound/core/pcm_native.c:502
snd_pcm_hw_param_mask sound/core/oss/pcm_oss.c:205 [inline]
snd_pcm_oss_change_params+0x8ce/0x3d10 sound/core/oss/pcm_oss.c:870
snd_pcm_oss_make_ready+0xe3/0x140 sound/core/oss/pcm_oss.c:1127
snd_pcm_oss_sync.isra.27+0x24b/0x850 sound/core/oss/pcm_oss.c:1651
snd_pcm_oss_release+0x214/0x290 sound/core/oss/pcm_oss.c:2446
__fput+0x34d/0x890 fs/file_table.c:209
____fput+0x15/0x20 fs/file_table.c:243
task_work_run+0x1e4/0x290 kernel/task_work.c:113
exit_task_work include/linux/task_work.h:22 [inline]
do_exit+0x1aee/0x2730 kernel/exit.c:865
do_group_exit+0x16f/0x430 kernel/exit.c:968
get_signal+0x886/0x1960 kernel/signal.c:2469
do_signal+0x90/0x2020 arch/x86/kernel/signal.c:810
exit_to_usermode_loop+0x28a/0x310 arch/x86/entry/common.c:162
prepare_exit_to_usermode arch/x86/entry/common.c:196 [inline]
syscall_return_slowpath arch/x86/entry/common.c:265 [inline]
do_syscall_64+0x792/0x9d0 arch/x86/entry/common.c:292
RIP: 0033:0x4552d9
RSP: 002b:00007fd689eb5c68 EFLAGS: 00000246 ORIG_RAX: 0000000000000010
RAX: 0000000000000000 RBX: 00007fd689eb66d4 RCX: 00000000004552d9
RDX: 0000000000000000 RSI: 0000000000004c81 RDI: 000000000000000f
RBP: 000000000072c010 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 00000000ffffffff
R13: 000000000000027d R14: 00000000006f6c58 R15: 0000000000000002

The buggy address belongs to the page:
page:ffffea0006c17980 count:0 mapcount:0 mapping:0000000000000000
flags: 0x2fffc0000000000()
raw: 02fffc0000000000 0000000000000000 ffff8801b05e69c0 00000000ffffffff
raw: dead000000000100 dead000000000200 ffff8801dad7f600 0000000000000000
page dumped because: kasan: bad access detected

Memory state around the buggy address:
ffff8801b05e6680: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
ffff8801b05e6700: 00 00 00 00 00 00 00 00 00 00 00 00 ca ca ca ca
> ffff8801b05e6780: 00 00 00 00 00 00 00 00 00 00 04 cb cb cb cb cb
ffff8801b05e6800: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
ffff8801b05e6880: 00 00 00 00 00 f1 f1 f1 f1 00 f2 f2 f2 f2 f2 f2

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