Re: [syzbot] linux-next boot error: KASAN: slab-out-of-bounds Read in _find_next_bit

From: Andrew Morton <akpm@linux-foundation.org>
To: syzbot <syzbot+08ca1fa706a22cc17efe@syzkaller.appspotmail.com>
Cc: linux-kernel@vger.kernel.org, linux-mm@kvack.org,
	linux-next@vger.kernel.org, sfr@canb.auug.org.au,
	syzkaller-bugs@googlegroups.com,
	Yury Norov <yury.norov@gmail.com>,
	Andrey Ryabinin <ryabinin.a.a@gmail.com>,
	Alexander Potapenko <glider@google.com>,
	Andrey Konovalov <andreyknvl@gmail.com>,
	Dmitry Vyukov <dvyukov@google.com>,
	Vincenzo Frascino <vincenzo.frascino@arm.com>
Subject: Re: [syzbot] linux-next boot error: KASAN: slab-out-of-bounds Read in _find_next_bit
Date: Tue, 6 Sep 2022 17:31:54 -0700	[thread overview]
Message-ID: <20220906173154.6f2664c8fc6b83470c5dfea1@linux-foundation.org> (raw)
In-Reply-To: <000000000000974e2805e802137e@google.com>

(cc Yury and KASAN developers)

On Tue, 06 Sep 2022 06:21:39 -0700 syzbot <syzbot+08ca1fa706a22cc17efe@syzkaller.appspotmail.com> wrote:

> Hello,
> 
> syzbot found the following issue on:
> 
> HEAD commit:    840126e36e8f Add linux-next specific files for 20220906
> git tree:       linux-next
> console output: https://syzkaller.appspot.com/x/log.txt?x=1216969b080000
> kernel config:  https://syzkaller.appspot.com/x/.config?x=239c4c4e44185526
> dashboard link: https://syzkaller.appspot.com/bug?extid=08ca1fa706a22cc17efe
> compiler:       gcc (Debian 10.2.1-6) 10.2.1 20210110, GNU ld (GNU Binutils for Debian) 2.35.2
> 
> Downloadable assets:
> disk image: https://storage.googleapis.com/syzbot-assets/1b9017e387a8/disk-840126e3.raw.xz
> vmlinux: https://storage.googleapis.com/syzbot-assets/12182558f88d/vmlinux-840126e3.xz
> 
> IMPORTANT: if you fix the issue, please add the following tag to the commit:
> Reported-by: syzbot+08ca1fa706a22cc17efe@syzkaller.appspotmail.com
> 
> ==================================================================
> BUG: KASAN: slab-out-of-bounds in _find_next_bit+0x143/0x160 lib/find_bit.c:109

Presumably the for_each_clear_bitrange() in pcpu_balance_populated().

> Read of size 8 at addr ffff8880175766b8 by task kworker/1:1/26

An eight byte read...

> CPU: 1 PID: 26 Comm: kworker/1:1 Not tainted 6.0.0-rc4-next-20220906-syzkaller #0
> Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 08/26/2022
> Workqueue: events pcpu_balance_workfn
> Call Trace:
>  <TASK>
>  __dump_stack lib/dump_stack.c:88 [inline]
>  dump_stack_lvl+0xcd/0x134 lib/dump_stack.c:106
>  print_address_description mm/kasan/report.c:287 [inline]
>  print_report+0x164/0x463 mm/kasan/report.c:398
>  kasan_report+0xbb/0x1f0 mm/kasan/report.c:486
>  _find_next_bit+0x143/0x160 lib/find_bit.c:109
>  find_next_bit include/linux/find.h:55 [inline]
>  pcpu_balance_populated mm/percpu.c:2086 [inline]
>  pcpu_balance_workfn+0x6c0/0xea0 mm/percpu.c:2246
>  process_one_work+0x991/0x1610 kernel/workqueue.c:2289
>  worker_thread+0x665/0x1080 kernel/workqueue.c:2436
>  kthread+0x2e4/0x3a0 kernel/kthread.c:376
>  ret_from_fork+0x1f/0x30 arch/x86/entry/entry_64.S:306
>  </TASK>
> 
> Allocated by task 26:
>  kasan_save_stack+0x1e/0x40 mm/kasan/common.c:45
>  kasan_set_track+0x21/0x30 mm/kasan/common.c:52
>  ____kasan_kmalloc mm/kasan/common.c:371 [inline]
>  ____kasan_kmalloc mm/kasan/common.c:330 [inline]
>  __kasan_kmalloc+0xa1/0xb0 mm/kasan/common.c:380
>  kasan_kmalloc include/linux/kasan.h:211 [inline]
>  __do_kmalloc_node mm/slab_common.c:931 [inline]
>  __kmalloc+0x54/0xc0 mm/slab_common.c:944
>  kmalloc include/linux/slab.h:565 [inline]
>  kzalloc include/linux/slab.h:696 [inline]
>  pcpu_mem_zalloc+0x70/0xa0 mm/percpu.c:514
>  pcpu_alloc_chunk mm/percpu.c:1446 [inline]
>  pcpu_create_chunk+0x23/0x930 mm/percpu-vm.c:338
>  pcpu_balance_populated mm/percpu.c:2108 [inline]
>  pcpu_balance_workfn+0xc4e/0xea0 mm/percpu.c:2246
>  process_one_work+0x991/0x1610 kernel/workqueue.c:2289
>  worker_thread+0x665/0x1080 kernel/workqueue.c:2436
>  kthread+0x2e4/0x3a0 kernel/kthread.c:376
>  ret_from_fork+0x1f/0x30 arch/x86/entry/entry_64.S:306
> 
> The buggy address belongs to the object at ffff888017576600
>  which belongs to the cache kmalloc-192 of size 192
> The buggy address is located 184 bytes inside of
>  192-byte region [ffff888017576600, ffff8880175766c0)

At offset 184 of a 192-byte region.

So what's wrong with doing that?  Does KASAN have an off-by-one?

> The buggy address belongs to the physical page:
> page:ffffea00005d5d80 refcount:1 mapcount:0 mapping:0000000000000000 index:0x0 pfn:0x17576
> flags: 0xfff00000000200(slab|node=0|zone=1|lastcpupid=0x7ff)
> raw: 00fff00000000200 ffff888011841a00 dead000000000122 0000000000000000
> raw: 0000000000000000 0000000080100010 00000001ffffffff 0000000000000000
> page dumped because: kasan: bad access detected
> page_owner tracks the page as allocated
> page last allocated via order 0, migratetype Unmovable, gfp_mask 0x12cc0(GFP_KERNEL|__GFP_NOWARN|__GFP_NORETRY), pid 1, tgid 1 (swapper/0), ts 2455007664, free_ts 0
>  prep_new_page mm/page_alloc.c:2544 [inline]
>  get_page_from_freelist+0x109b/0x2ce0 mm/page_alloc.c:4294
>  __alloc_pages+0x1c7/0x510 mm/page_alloc.c:5552
>  alloc_page_interleave+0x1e/0x200 mm/mempolicy.c:2113
>  alloc_pages+0x22f/0x270 mm/mempolicy.c:2275
>  alloc_slab_page mm/slub.c:1734 [inline]
>  allocate_slab+0x213/0x300 mm/slub.c:1879
>  new_slab mm/slub.c:1932 [inline]
>  ___slab_alloc+0xad0/0x1440 mm/slub.c:3113
>  __slab_alloc.constprop.0+0x4d/0xa0 mm/slub.c:3211
>  slab_alloc_node mm/slub.c:3296 [inline]
>  __kmem_cache_alloc_node+0x18a/0x3d0 mm/slub.c:3369
>  __do_kmalloc_node mm/slab_common.c:930 [inline]
>  __kmalloc_node_track_caller+0x45/0xc0 mm/slab_common.c:951
>  __do_krealloc mm/slab_common.c:1324 [inline]
>  krealloc+0x8c/0xf0 mm/slab_common.c:1357
>  add_sysfs_param+0xca/0x960 kernel/params.c:651
>  kernel_add_sysfs_param kernel/params.c:812 [inline]
>  param_sysfs_builtin kernel/params.c:851 [inline]
>  param_sysfs_init+0x301/0x43b kernel/params.c:970
>  do_one_initcall+0xfe/0x650 init/main.c:1307
>  do_initcall_level init/main.c:1382 [inline]
>  do_initcalls init/main.c:1398 [inline]
>  do_basic_setup init/main.c:1417 [inline]
>  kernel_init_freeable+0x6ff/0x788 init/main.c:1637
>  kernel_init+0x1a/0x1d0 init/main.c:1525
>  ret_from_fork+0x1f/0x30 arch/x86/entry/entry_64.S:306
> page_owner free stack trace missing
> 
> Memory state around the buggy address:
>  ffff888017576580: fb fb fb fb fb fb fb fb fc fc fc fc fc fc fc fc
>  ffff888017576600: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
> >ffff888017576680: 00 00 00 00 00 00 00 fc fc fc fc fc fc fc fc fc
>                                         ^
>  ffff888017576700: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
>  ffff888017576780: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
> ==================================================================
> 
> 
> ---
> This report is generated by a bot. It may contain errors.
> See https://goo.gl/tpsmEJ for more information about syzbot.
> syzbot engineers can be reached at syzkaller@googlegroups.com.
> 
> syzbot will keep track of this issue. See:
> https://goo.gl/tpsmEJ#status for how to communicate with syzbot.