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

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

[syzbot]

Hello,

syzbot found the following crash on:

HEAD commit:    05679ca6 xdp: Prevent overflow in devmap_hash cost calcula..
git tree:       bpf
console output: https://syzkaller.appspot.com/x/log.txt?x=12d37fcf600000
kernel config:  https://syzkaller.appspot.com/x/.config?x=ebb95b9e9f5291dd
dashboard link: https://syzkaller.appspot.com/bug?extid=357de617b97752833bd5
compiler:       gcc (GCC) 9.0.0 20181231 (experimental)

Unfortunately, I don't have any reproducer for this crash yet.

IMPORTANT: if you fix the bug, please add the following tag to the commit:
Reported-by: syzbot+357de617b97752833bd5@syzkaller.appspotmail.com

==================================================================
BUG: KASAN: stack-out-of-bounds in finish_writeback_work.isra.0+0x11b/0x120  
fs/fs-writeback.c:168
Read of size 8 at addr ffff88806f04f9c8 by task kworker/u4:2/33

CPU: 1 PID: 33 Comm: kworker/u4:2 Not tainted 5.4.0-rc1+ #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS  
Google 01/01/2011
Workqueue: writeback wb_workfn (flush-8:0)
Call Trace:
  __dump_stack lib/dump_stack.c:77 [inline]
  dump_stack+0x172/0x1f0 lib/dump_stack.c:113
  print_address_description.constprop.0.cold+0xd4/0x30b mm/kasan/report.c:374
  __kasan_report.cold+0x1b/0x41 mm/kasan/report.c:506
  kasan_report+0x12/0x20 mm/kasan/common.c:634
  __asan_report_load8_noabort+0x14/0x20 mm/kasan/generic_report.c:132
  finish_writeback_work.isra.0+0x11b/0x120 fs/fs-writeback.c:168
  wb_do_writeback fs/fs-writeback.c:2030 [inline]
  wb_workfn+0x34f/0x1220 fs/fs-writeback.c:2070
  process_one_work+0x9af/0x1740 kernel/workqueue.c:2269
  worker_thread+0x98/0xe40 kernel/workqueue.c:2415
  kthread+0x361/0x430 kernel/kthread.c:255
  ret_from_fork+0x24/0x30 arch/x86/entry/entry_64.S:352

The buggy address belongs to the page:
page:ffffea0001bc13c0 refcount:0 mapcount:0 mapping:0000000000000000  
index:0x0
flags: 0x1fffc0000000000()
raw: 01fffc0000000000 0000000000000000 ffffffff01bc0101 0000000000000000
raw: 0000000000000000 0000000000000000 00000000ffffffff 0000000000000000
page dumped because: kasan: bad access detected

Memory state around the buggy address:
  ffff88806f04f880: 00 00 00 00 00 00 00 00 00 00 00 00 00 f1 f1 f1
  ffff88806f04f900: f1 00 00 f3 f3 00 00 00 00 00 00 00 00 00 00 00
> ffff88806f04f980: 00 00 00 00 00 00 00 00 f1 f1 f1 f1 00 f3 f3 f3
                                               ^
  ffff88806f04fa00: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 f1
  ffff88806f04fa80: f1 f1 f1 00 f2 f2 f2 00 00 00 00 00 00 00 00 00
==================================================================


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