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BUG: KASAN: stack-out-of-bounds in csd_lock_record+0xcb/0xe0 kernel/smp.c:118
Read of size 8 at addr ffffc90000dd7970 by task syz-executor.4/30450

CPU: 1 PID: 30450 Comm: syz-executor.4 Not tainted 5.8.0-rc3-next-20200703-syzkaller #0
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+0x18f/0x20d lib/dump_stack.c:118
 print_address_description.constprop.0.cold+0x5/0x436 mm/kasan/report.c:383
 __kasan_report mm/kasan/report.c:513 [inline]
 kasan_report.cold+0x1f/0x37 mm/kasan/report.c:530
 csd_lock_record+0xcb/0xe0 kernel/smp.c:118
 flush_smp_call_function_queue+0x285/0x730 kernel/smp.c:391
 __sysvec_call_function_single+0x98/0x490 arch/x86/kernel/smp.c:248
 asm_call_on_stack+0xf/0x20 arch/x86/entry/entry_64.S:706
 </IRQ>
 __run_on_irqstack arch/x86/include/asm/irq_stack.h:22 [inline]
 run_on_irqstack_cond arch/x86/include/asm/irq_stack.h:48 [inline]
 sysvec_call_function_single+0xe0/0x120 arch/x86/kernel/smp.c:243
 asm_sysvec_call_function_single+0x12/0x20 arch/x86/include/asm/idtentry.h:604
RIP: 0010:tun_flow_flush+0x1b4/0x240 drivers/net/tun.c:424
Code: 74 04 3c 03 7e 67 41 83 ad 38 29 00 00 01 4d 85 e4 0f 85 00 ff ff ff e8 8a bb b0 fc bf 00 04 00 00 83 44 24 1c 01 8b 5c 24 1c <89> de e8 f5 b7 b0 fc 48 83 44 24 10 08 81 fb 00 04 00 00 0f 85 93
RSP: 0018:ffffc9001624fcc0 EFLAGS: 00000206
RAX: 0000000000000000 RBX: 0000000000000255 RCX: ffffffff84c34b8b
RDX: ffff888046000100 RSI: ffffffff84c34b76 RDI: 0000000000000400
RBP: dffffc0000000000 R08: 0000000000000001 R09: 0000000000000003
R10: 0000000000000400 R11: 0000000000000000 R12: ffff8880459cb500
R13: ffff8880459c8bc0 R14: 0000000000000002 R15: dffffc0000000000
 tun_flow_uninit drivers/net/tun.c:1341 [inline]
 tun_free_netdev+0xb2/0x140 drivers/net/tun.c:2277
 netdev_run_todo+0x6be/0xac0 net/core/dev.c:9795
 tun_detach drivers/net/tun.c:711 [inline]
 tun_chr_close+0xf5/0x180 drivers/net/tun.c:3423
 __fput+0x33c/0x880 fs/file_table.c:281
 task_work_run+0xdd/0x190 kernel/task_work.c:135
 tracehook_notify_resume include/linux/tracehook.h:188 [inline]
 exit_to_usermode_loop arch/x86/entry/common.c:222 [inline]
 __prepare_exit_to_usermode+0x1e9/0x1f0 arch/x86/entry/common.c:252
 do_syscall_64+0x6c/0xe0 arch/x86/entry/common.c:376
 entry_SYSCALL_64_after_hwframe+0x44/0xa9
RIP: 0033:0x416721
Code: Bad RIP value.
RSP: 002b:00007ffdf409b520 EFLAGS: 00000293 ORIG_RAX: 0000000000000003
RAX: 0000000000000000 RBX: 0000000000000004 RCX: 0000000000416721
RDX: 0000000000000000 RSI: 00000000000019e3 RDI: 0000000000000003
RBP: 0000000000000001 R08: 00000000dbf7f9e3 R09: 00000000dbf7f9e7
R10: 00007ffdf409b610 R11: 0000000000000293 R12: 0000000000790358
R13: 00000000003747b4 R14: ffffffffffffffff R15: 000000000078bf0c


Memory state around the buggy address:
 ffffc90000dd7800: 00 00 00 00 00 00 00 00 00 00 00 00 f1 f1 f1 f1
 ffffc90000dd7880: 00 00 00 00 00 00 00 00 00 00 00 f3 f3 f3 f3 f3
>ffffc90000dd7900: 00 00 00 00 00 00 00 00 00 00 00 00 00 f1 f1 f1
                                                             ^
 ffffc90000dd7980: f1 00 00 00 f3 f3 f3 f3 f3 00 00 00 00 00 00 00
 ffffc90000dd7a00: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
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