Date:   Tue, 5 Mar 2019 14:42:00 +0800
From:   zhong jiang <zhongjiang@...wei.com>
To:     Dmitry Vyukov <dvyukov@...gle.com>
CC:     syzbot <syzbot+cbb52e396df3e565ab02@...kaller.appspotmail.com>,
        "Michal Hocko" <mhocko@...nel.org>,
        Andrea Arcangeli <aarcange@...hat.com>,
        <cgroups@...r.kernel.org>, Johannes Weiner <hannes@...xchg.org>,
        LKML <linux-kernel@...r.kernel.org>,
        Linux-MM <linux-mm@...ck.org>,
        syzkaller-bugs <syzkaller-bugs@...glegroups.com>,
        Vladimir Davydov <vdavydov.dev@...il.com>,
        David Rientjes <rientjes@...gle.com>,
        Hugh Dickins <hughd@...gle.com>,
        Matthew Wilcox <willy@...radead.org>,
        Mel Gorman <mgorman@...e.de>,
        "Vlastimil Babka" <vbabka@...e.cz>
Subject: Re: KASAN: use-after-free Read in get_mem_cgroup_from_mm

On 2019/3/5 14:26, Dmitry Vyukov wrote:
> On Mon, Mar 4, 2019 at 4:32 PM zhong jiang <zhongjiang@...wei.com> wrote:
>> On 2019/3/4 22:11, Dmitry Vyukov wrote:
>>> On Mon, Mar 4, 2019 at 3:00 PM zhong jiang <zhongjiang@...wei.com> wrote:
>>>> On 2019/3/4 15:40, Dmitry Vyukov wrote:
>>>>> On Sun, Mar 3, 2019 at 5:19 PM zhong jiang <zhongjiang@...wei.com> wrote:
>>>>>> Hi, guys
>>>>>>
>>>>>> I also hit the following issue. but it fails to reproduce the issue by the log.
>>>>>>
>>>>>> it seems to the case that we access the mm->owner and deference it will result in the UAF.
>>>>>> But it should not be possible that we specify the incomplete process to be the mm->owner.
>>>>>>
>>>>>> Any thoughts?
>>>>> FWIW syzbot was able to reproduce this with this reproducer.
>>>>> This looks like a very subtle race (threaded reproducer that runs
>>>>> repeatedly in multiple processes), so most likely we are looking for
>>>>> something like few instructions inconsistency window.
>>>>>
>>>> I has a little doubtful about the instrustions inconsistency window.
>>>>
>>>> I guess that you mean some smb barriers should be taken into account.:-)
>>>>
>>>> Because IMO, It should not be the lock case to result in the issue.
>>> Since the crash was triggered on x86 _most likley_ this is not a
>>> missed barrier. What I meant is that one thread needs to executed some
>>> code, while another thread is stopped within few instructions.
>>>
>>>
>> It is weird and I can not find any relationship you had said with the issue.:-(
>>
>> Because It is the cause that mm->owner has been freed, whereas we still deference it.
>>
>> From the lastest freed task call trace, It fails to create process.
>>
>> Am I miss something or I misunderstand your meaning. Please correct me.
> Your analysis looks correct. I am just saying that the root cause of
> this use-after-free seems to be a race condition.
>
>
>
Yep, Indeed,  I can not figure out how the race works. I will dig up further.

Thanks,
zhong jiang
>
>>>>>> On 2018/12/4 23:43, syzbot wrote:
>>>>>>> syzbot has found a reproducer for the following crash on:
>>>>>>>
>>>>>>> HEAD commit:    0072a0c14d5b Merge tag 'media/v4.20-4' of git://git.kernel..
>>>>>>> git tree:       upstream
>>>>>>> console output: https://syzkaller.appspot.com/x/log.txt?x=11c885a3400000
>>>>>>> kernel config:  https://syzkaller.appspot.com/x/.config?x=b9cc5a440391cbfd
>>>>>>> dashboard link: https://syzkaller.appspot.com/bug?extid=cbb52e396df3e565ab02
>>>>>>> compiler:       gcc (GCC) 8.0.1 20180413 (experimental)
>>>>>>> syz repro:      https://syzkaller.appspot.com/x/repro.syz?x=12835e25400000
>>>>>>> C reproducer:   https://syzkaller.appspot.com/x/repro.c?x=172fa5a3400000
>>>>>>>
>>>>>>> IMPORTANT: if you fix the bug, please add the following tag to the commit:
>>>>>>> Reported-by: syzbot+cbb52e396df3e565ab02@...kaller.appspotmail.com
>>>>>>>
>>>>>>> cgroup: fork rejected by pids controller in /syz2
>>>>>>> ==================================================================
>>>>>>> BUG: KASAN: use-after-free in __read_once_size include/linux/compiler.h:182 [inline]
>>>>>>> BUG: KASAN: use-after-free in task_css include/linux/cgroup.h:477 [inline]
>>>>>>> BUG: KASAN: use-after-free in mem_cgroup_from_task mm/memcontrol.c:815 [inline]
>>>>>>> BUG: KASAN: use-after-free in get_mem_cgroup_from_mm.part.62+0x6d7/0x880 mm/memcontrol.c:844
>>>>>>> Read of size 8 at addr ffff8881b72af310 by task syz-executor198/9332
>>>>>>>
>>>>>>> CPU: 0 PID: 9332 Comm: syz-executor198 Not tainted 4.20.0-rc5+ #142
>>>>>>> Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
>>>>>>> Call Trace:
>>>>>>>  __dump_stack lib/dump_stack.c:77 [inline]
>>>>>>>  dump_stack+0x244/0x39d lib/dump_stack.c:113
>>>>>>>  print_address_description.cold.7+0x9/0x1ff mm/kasan/report.c:256
>>>>>>>  kasan_report_error mm/kasan/report.c:354 [inline]
>>>>>>>  kasan_report.cold.8+0x242/0x309 mm/kasan/report.c:412
>>>>>>>  __asan_report_load8_noabort+0x14/0x20 mm/kasan/report.c:433
>>>>>>>  __read_once_size include/linux/compiler.h:182 [inline]
>>>>>>>  task_css include/linux/cgroup.h:477 [inline]
>>>>>>>  mem_cgroup_from_task mm/memcontrol.c:815 [inline]
>>>>>>>  get_mem_cgroup_from_mm.part.62+0x6d7/0x880 mm/memcontrol.c:844
>>>>>>>  get_mem_cgroup_from_mm mm/memcontrol.c:834 [inline]
>>>>>>>  mem_cgroup_try_charge+0x608/0xe20 mm/memcontrol.c:5888
>>>>>>>  mcopy_atomic_pte mm/userfaultfd.c:71 [inline]
>>>>>>>  mfill_atomic_pte mm/userfaultfd.c:418 [inline]
>>>>>>>  __mcopy_atomic mm/userfaultfd.c:559 [inline]
>>>>>>>  mcopy_atomic+0xb08/0x2c70 mm/userfaultfd.c:609
>>>>>>>  userfaultfd_copy fs/userfaultfd.c:1705 [inline]
>>>>>>>  userfaultfd_ioctl+0x29fb/0x5610 fs/userfaultfd.c:1851
>>>>>>>  vfs_ioctl fs/ioctl.c:46 [inline]
>>>>>>>  file_ioctl fs/ioctl.c:509 [inline]
>>>>>>>  do_vfs_ioctl+0x1de/0x1790 fs/ioctl.c:696
>>>>>>>  ksys_ioctl+0xa9/0xd0 fs/ioctl.c:713
>>>>>>>  __do_sys_ioctl fs/ioctl.c:720 [inline]
>>>>>>>  __se_sys_ioctl fs/ioctl.c:718 [inline]
>>>>>>>  __x64_sys_ioctl+0x73/0xb0 fs/ioctl.c:718
>>>>>>>  do_syscall_64+0x1b9/0x820 arch/x86/entry/common.c:290
>>>>>>>  entry_SYSCALL_64_after_hwframe+0x49/0xbe
>>>>>>> RIP: 0033:0x44c7e9
>>>>>>> Code: 5d c5 fb ff c3 66 2e 0f 1f 84 00 00 00 00 00 66 90 48 89 f8 48 89 f7 48 89 d6 48 89 ca 4d 89 c2 4d 89 c8 4c 8b 4c 24 08 0f 05 <48> 3d 01 f0 ff ff 0f 83 2b c5 fb ff c3 66 2e 0f 1f 84 00 00 00 00
>>>>>>> RSP: 002b:00007f906b69fdb8 EFLAGS: 00000246 ORIG_RAX: 0000000000000010
>>>>>>> RAX: ffffffffffffffda RBX: 00000000006e4a08 RCX: 000000000044c7e9
>>>>>>> RDX: 0000000020000100 RSI: 00000000c028aa03 RDI: 0000000000000004
>>>>>>> RBP: 00000000006e4a00 R08: 0000000000000000 R09: 0000000000000000
>>>>>>> R10: 0000000000000000 R11: 0000000000000246 R12: 00000000006e4a0c
>>>>>>> R13: 00007ffdfd47813f R14: 00007f906b6a09c0 R15: 000000000000002d
>>>>>>>
>>>>>>> Allocated by task 9325:
>>>>>>>  save_stack+0x43/0xd0 mm/kasan/kasan.c:448
>>>>>>>  set_track mm/kasan/kasan.c:460 [inline]
>>>>>>>  kasan_kmalloc+0xc7/0xe0 mm/kasan/kasan.c:553
>>>>>>>  kasan_slab_alloc+0x12/0x20 mm/kasan/kasan.c:490
>>>>>>>  kmem_cache_alloc_node+0x144/0x730 mm/slab.c:3644
>>>>>>>  alloc_task_struct_node kernel/fork.c:158 [inline]
>>>>>>>  dup_task_struct kernel/fork.c:843 [inline]
>>>>>>>  copy_process+0x2026/0x87a0 kernel/fork.c:1751
>>>>>>>  _do_fork+0x1cb/0x11d0 kernel/fork.c:2216
>>>>>>>  __do_sys_clone kernel/fork.c:2323 [inline]
>>>>>>>  __se_sys_clone kernel/fork.c:2317 [inline]
>>>>>>>  __x64_sys_clone+0xbf/0x150 kernel/fork.c:2317
>>>>>>>  do_syscall_64+0x1b9/0x820 arch/x86/entry/common.c:290
>>>>>>>  entry_SYSCALL_64_after_hwframe+0x49/0xbe
>>>>>>>
>>>>>>> Freed by task 9325:
>>>>>>>  save_stack+0x43/0xd0 mm/kasan/kasan.c:448
>>>>>>>  set_track mm/kasan/kasan.c:460 [inline]
>>>>>>>  __kasan_slab_free+0x102/0x150 mm/kasan/kasan.c:521
>>>>>>>  kasan_slab_free+0xe/0x10 mm/kasan/kasan.c:528
>>>>>>>  __cache_free mm/slab.c:3498 [inline]
>>>>>>>  kmem_cache_free+0x83/0x290 mm/slab.c:3760
>>>>>>>  free_task_struct kernel/fork.c:163 [inline]
>>>>>>>  free_task+0x16e/0x1f0 kernel/fork.c:457
>>>>>>>  copy_process+0x1dcc/0x87a0 kernel/fork.c:2148
>>>>>>>  _do_fork+0x1cb/0x11d0 kernel/fork.c:2216
>>>>>>>  __do_sys_clone kernel/fork.c:2323 [inline]
>>>>>>>  __se_sys_clone kernel/fork.c:2317 [inline]
>>>>>>>  __x64_sys_clone+0xbf/0x150 kernel/fork.c:2317
>>>>>>>  do_syscall_64+0x1b9/0x820 arch/x86/entry/common.c:290
>>>>>>>  entry_SYSCALL_64_after_hwframe+0x49/0xbe
>>>>>>>
>>>>>>> The buggy address belongs to the object at ffff8881b72ae240
>>>>>>>  which belongs to the cache task_struct(81:syz2) of size 6080
>>>>>>> The buggy address is located 4304 bytes inside of
>>>>>>>  6080-byte region [ffff8881b72ae240, ffff8881b72afa00)
>>>>>>> The buggy address belongs to the page:
>>>>>>> page:ffffea0006dcab80 count:1 mapcount:0 mapping:ffff8881d2dce0c0 index:0x0 compound_mapcount: 0
>>>>>>> flags: 0x2fffc0000010200(slab|head)
>>>>>>> raw: 02fffc0000010200 ffffea00074a1f88 ffffea0006ebbb88 ffff8881d2dce0c0
>>>>>>> raw: 0000000000000000 ffff8881b72ae240 0000000100000001 ffff8881d87fe580
>>>>>>> page dumped because: kasan: bad access detected
>>>>>>> page->mem_cgroup:ffff8881d87fe580
>>>>>>>
>>>>>>> Memory state around the buggy address:
>>>>>>>  ffff8881b72af200: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
>>>>>>>  ffff8881b72af280: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
>>>>>>>> ffff8881b72af300: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
>>>>>>>                          ^
>>>>>>>  ffff8881b72af380: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
>>>>>>>  ffff8881b72af400: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
>>>>>>> ==================================================================
>>>>>>>
>>>>>>>
>>>>>>> .
>>>>>>>
>>>>>> --
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>>>>>> To view this discussion on the web visit https://groups.google.com/d/msgid/syzkaller-bugs/5C7BFE94.6070500%40huawei.com.
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>>>>> .
>>>>>
>>> .
>>>
>>
> .
>

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