Re: [PATCH v4] mm: hugetlb: fix UAF in hugetlb_handle_userfault

[Liu Shixin <liushixin2@huawei.com>]

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.
> .
>