KASAN: stack-out-of-bounds Read in timerqueue_add

[syzbot]

Hello,

syzbot found the following crash on:

HEAD commit:    fc36def997cf mm: teach dump_page() to correctly output poi..
git tree:       upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=167e3b92400000
kernel config:  https://syzkaller.appspot.com/x/.config?x=f62553dc846b0692
dashboard link: https://syzkaller.appspot.com/bug?extid=b680e42077a0d7c9a0c4
compiler:       gcc (GCC) 8.0.1 20180413 (experimental)
syzkaller repro:https://syzkaller.appspot.com/x/repro.syz?x=1030a858400000
C reproducer:   https://syzkaller.appspot.com/x/repro.c?x=1167aaa4400000

IMPORTANT: if you fix the bug, please add the following tag to the commit:
Reported-by: syzbot+b680e42077a0d7c9a0c4@xxxxxxxxxxxxxxxxxxxxxxxxx

random: sshd: uninitialized urandom read (32 bytes read)
random: sshd: uninitialized urandom read (32 bytes read)
random: sshd: uninitialized urandom read (32 bytes read)
IPVS: ftp: loaded support on port[0] = 21
==================================================================
BUG: KASAN: stack-out-of-bounds in timerqueue_add+0x249/0x2b0  
lib/timerqueue.c:52
Read of size 8 at addr ffff8801af537cf8 by task syz-executor591/7178

CPU: 0 PID: 7178 Comm: syz-executor591 Not tainted 4.18.0-rc3+ #130
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+0x1c9/0x2b4 lib/dump_stack.c:113
 print_address_description+0x6c/0x20b mm/kasan/report.c:256
 kasan_report_error mm/kasan/report.c:354 [inline]
 kasan_report.cold.7+0x242/0x2fe mm/kasan/report.c:412
 __asan_report_load8_noabort+0x14/0x20 mm/kasan/report.c:433
 timerqueue_add+0x249/0x2b0 lib/timerqueue.c:52
 enqueue_hrtimer+0x18e/0x540 kernel/time/hrtimer.c:960
 __run_hrtimer kernel/time/hrtimer.c:1413 [inline]
 __hrtimer_run_queues+0xc07/0x10c0 kernel/time/hrtimer.c:1460
 hrtimer_interrupt+0x2f3/0x750 kernel/time/hrtimer.c:1518
 local_apic_timer_interrupt arch/x86/kernel/apic/apic.c:1025 [inline]
 smp_apic_timer_interrupt+0x165/0x730 arch/x86/kernel/apic/apic.c:1050
 apic_timer_interrupt+0xf/0x20 arch/x86/entry/entry_64.S:863
 </IRQ>

The buggy address belongs to the page:
page:ffffea0006bd4dc0 count:0 mapcount:0 mapping:0000000000000000 index:0x0
flags: 0x2fffc0000000000()
raw: 02fffc0000000000 0000000000000000 ffffffff06bd0101 0000000000000000
raw: 0000000000000000 0000000000000000 00000000ffffffff 0000000000000000
page dumped because: kasan: bad access detected

Memory state around the buggy address:
 ffff8801af537b80: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
 ffff8801af537c00: 00 00 00 00 f1 f1 f1 f1 00 f2 f2 f2 f2 f2 f2 f2
> ffff8801af537c80: 00 f2 f2 f2 f2 f2 f2 f2 00 f2 f2 f2 f2 f2 f2 f2
                                                                ^
 ffff8801af537d00: f8 f2 f2 f2 f2 f2 f2 f2 00 f2 f2 f2 00 00 00 00
 ffff8801af537d80: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
==================================================================


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