==================================================================
BUG: KASAN: out-of-bounds in unwind_next_frame+0x169f/0x1810 arch/x86/kernel/unwind_orc.c:470
Read of size 8 at addr ffff8881a3b27e78 by task syz-executor.0/21505

CPU: 0 PID: 21505 Comm: syz-executor.0 Not tainted 4.14.138+ #30
Call Trace:
 __dump_stack lib/dump_stack.c:17 [inline]
 dump_stack+0xca/0x134 lib/dump_stack.c:53
 print_address_description+0x60/0x226 mm/kasan/report.c:187
 __kasan_report.cold+0x1a/0x41 mm/kasan/report.c:316
 unwind_next_frame+0x169f/0x1810 arch/x86/kernel/unwind_orc.c:470
 __save_stack_trace+0x7a/0xf0 arch/x86/kernel/stacktrace.c:44
 save_stack_trace_tsk arch/x86/kernel/stacktrace.c:73 [inline]
 save_stack_trace_tsk+0x34/0x40 arch/x86/kernel/stacktrace.c:68
 proc_pid_stack+0x194/0x270 fs/proc/base.c:460
 proc_single_show+0xf1/0x160 fs/proc/base.c:762
 seq_read+0x4f7/0x1180 fs/seq_file.c:237
 do_loop_readv_writev fs/read_write.c:699 [inline]
 do_loop_readv_writev fs/read_write.c:686 [inline]
 do_iter_read+0x3e8/0x5b0 fs/read_write.c:923
 vfs_readv+0xe6/0x150 fs/read_write.c:985
 do_preadv+0x189/0x230 fs/read_write.c:1069
 do_syscall_64+0x19b/0x520 arch/x86/entry/common.c:292
 entry_SYSCALL_64_after_hwframe+0x42/0xb7
RIP: 0033:0x459829
RSP: 002b:00007f15b2a58c78 EFLAGS: 00000246 ORIG_RAX: 0000000000000127
RAX: ffffffffffffffda RBX: 0000000000000004 RCX: 0000000000459829
RDX: 10000000000002a1 RSI: 0000000020000480 RDI: 0000000000000004
RBP: 000000000075bfc8 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 00007f15b2a596d4
R13: 00000000004c6b38 R14: 00000000004dbcc8 R15: 00000000ffffffff

The buggy address belongs to the page:
page:ffffea00068ec9c0 count:0 mapcount:0 mapping:          (null) index:0x0
flags: 0x4000000000000000()
raw: 4000000000000000 0000000000000000 0000000000000000 00000000ffffffff
raw: 0000000000000000 0000000100000001 0000000000000000 0000000000000000
page dumped because: kasan: bad access detected

Memory state around the buggy address:
 ffff8881a3b27d00: 00 f3 f3 f3 f3 00 00 00 00 00 00 00 00 00 00 00
 ffff8881a3b27d80: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
>ffff8881a3b27e00: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
                                                                ^
 ffff8881a3b27e80: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
 ffff8881a3b27f00: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
==================================================================