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Subject: Re: [PATCH v4] mm: hugetlb: fix UAF in hugetlb_handle_userfault
To:     Andrew Morton <akpm@linux-foundation.org>
References: <20220924034905.2694686-1-liushixin2@huawei.com>
 <20220925112826.c3efd2cf438d1bb6329f78ed@linux-foundation.org>
CC:     Liu Zixian <liuzixian4@huawei.com>,
        Mike Kravetz <mike.kravetz@oracle.com>,
        Muchun Song <songmuchun@bytedance.com>,
        "Sidhartha Kumar" <sidhartha.kumar@oracle.com>,
        John Hubbard <jhubbard@nvidia.com>,
        "David Hildenbrand" <david@redhat.com>,
        Kefeng Wang <wangkefeng.wang@huawei.com>, <linux-mm@kvack.org>,
        <linux-kernel@vger.kernel.org>
From:   Liu Shixin <liushixin2@huawei.com>
Message-ID: <174f5998-1f1d-c283-26bb-82c5a68150ab@huawei.com>
Date:   Mon, 26 Sep 2022 14:48:27 +0800
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On 2022/9/26 2:28, Andrew Morton wrote:
> On Sat, 24 Sep 2022 11:49:05 +0800 Liu Shixin <liushixin2@huawei.com> wrote:
>
>> The vma_lock and hugetlb_fault_mutex are dropped before handling
>> userfault and reacquire them again after handle_userfault(), but
>> reacquire the vma_lock could lead to UAF[1,2] due to the following
>> race,
>>
>> hugetlb_fault
>>   hugetlb_no_page
>>     /*unlock vma_lock */
>>     hugetlb_handle_userfault
>>       handle_userfault
>>         /* unlock mm->mmap_lock*/
>>                                            vm_mmap_pgoff
>>                                              do_mmap
>>                                                mmap_region
>>                                                  munmap_vma_range
>>                                                    /* clean old vma */
>>         /* lock vma_lock again  <--- UAF */
>>     /* unlock vma_lock */
>>
>> Since the vma_lock will unlock immediately after hugetlb_handle_userfault(),
>> let's drop the unneeded lock and unlock in hugetlb_handle_userfault() to fix
>> the issue.
>>
> Thanks.  Turns out that porting all the pending material on top of this
> change was not a confidence-inspiring activity.  So I ended up merging
> your v3.  Please work with Greg on the backporting when he gets on to
> it?  Hopefully that will merely involve sending him this v4.
OK, I'll do it.
> .
>