linux-kernel - Re: [PATCH] mm/hugetlb: fix null ptr defer in hugetlb_vma_lock

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <20231103023737.GC3531@monkey>
Date:   Thu, 2 Nov 2023 19:37:37 -0700
From:   Mike Kravetz <mike.kravetz@...cle.com>
To:     Rik van Riel <riel@...riel.com>
Cc:     Edward Adam Davis <eadavis@...com>, akpm@...ux-foundation.org,
        linux-kernel@...r.kernel.org, linux-mm@...ck.org,
        llvm@...ts.linux.dev, muchun.song@...ux.dev, nathan@...nel.org,
        ndesaulniers@...gle.com,
        syzbot+6ada951e7c0f7bc8a71e@...kaller.appspotmail.com,
        syzkaller-bugs@...glegroups.com, trix@...hat.com
Subject: Re: [PATCH] mm/hugetlb: fix null ptr defer in hugetlb_vma_lock_write

On 11/02/23 19:24, Mike Kravetz wrote:
> 
> In the specific case causing the null-ptr-deref, the resv_map pointer
> (vm_private_data) is NULL.

Hi Rik,

In commit bf4916922c60 hugetlbfs: extend hugetlb_vma_lock to private VMAs,
it correctly says:

    Extend the locking scheme used to protect shared hugetlb mappings from
    truncate vs page fault races, in order to protect private hugetlb mappings
    (with resv_map) against MADV_DONTNEED.

That qualification '(with resv_map)' caught my attention originally, and
I thought about it again while looking into this.  We now cover the common
cases, but there are still quite a few cases where resv_map is NULL for
private mappings.  In such cases, the race between MADV_DONTNEED and page
fault still exists.  Is that a concern?

With a bit more work we 'could' make sure every hugetlb vma has a lock
to participate in this scheme.

Any thhoughts?
-- 
Mike Kravetz