linux-kernel - Re: [PATCH v4] mm: hugetlb: fix UAF in hugetlb_handle

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Message-Id: <20220925112826.c3efd2cf438d1bb6329f78ed@linux-foundation.org>
Date:   Sun, 25 Sep 2022 11:28:26 -0700
From:   Andrew Morton <akpm@...ux-foundation.org>
To:     Liu Shixin <liushixin2@...wei.com>
Cc:     Liu Zixian <liuzixian4@...wei.com>,
        Mike Kravetz <mike.kravetz@...cle.com>,
        Muchun Song <songmuchun@...edance.com>,
        Sidhartha Kumar <sidhartha.kumar@...cle.com>,
        John Hubbard <jhubbard@...dia.com>,
        "David Hildenbrand" <david@...hat.com>,
        Kefeng Wang <wangkefeng.wang@...wei.com>, <linux-mm@...ck.org>,
        <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v4] mm: hugetlb: fix UAF in hugetlb_handle_userfault

On Sat, 24 Sep 2022 11:49:05 +0800 Liu Shixin <liushixin2@...wei.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.