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From:   Suren Baghdasaryan <surenb@google.com>
Date:   Tue, 15 Feb 2022 15:02:54 -0800
Message-ID: <CAJuCfpGG9zwbvfH5UZkt6cG=woeO0RGE7QxjEpXn=gFhiaDdmQ@mail.gmail.com>
Subject: Re: [PATCH v3 1/1] mm: fix use-after-free when anon vma name is used
 after vma is freed
To:     Michal Hocko <mhocko@suse.com>
Cc:     Andrew Morton <akpm@linux-foundation.org>,
        Colin Cross <ccross@google.com>,
        Sumit Semwal <sumit.semwal@linaro.org>,
        Dave Hansen <dave.hansen@intel.com>,
        Kees Cook <keescook@chromium.org>,
        Matthew Wilcox <willy@infradead.org>,
        "Kirill A . Shutemov" <kirill.shutemov@linux.intel.com>,
        Vlastimil Babka <vbabka@suse.cz>,
        Johannes Weiner <hannes@cmpxchg.org>,
        "Eric W. Biederman" <ebiederm@xmission.com>,
        Christian Brauner <brauner@kernel.org>, legion@kernel.org,
        ran.xiaokai@zte.com.cn, sashal@kernel.org,
        Chris Hyser <chris.hyser@oracle.com>,
        Davidlohr Bueso <dave@stgolabs.net>,
        Peter Collingbourne <pcc@google.com>, caoxiaofeng@yulong.com,
        David Hildenbrand <david@redhat.com>,
        Cyrill Gorcunov <gorcunov@gmail.com>,
        linux-mm <linux-mm@kvack.org>,
        LKML <linux-kernel@vger.kernel.org>,
        kernel-team <kernel-team@android.com>,
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On Tue, Feb 15, 2022 at 12:05 PM Michal Hocko <mhocko@suse.com> wrote:
>
> One thing I was considering is to check agains ref counte overflo (a
> deep process chain with many vmas could grow really high. ref_count
> interface doesn't provide any easy way to check for overflows as far as
> I could see from a quick glance so I gave up there but the logic would
> be really straightforward. We just create a new anon_vma_name with the same
> content and use it when duplicating if the usage grow really
> (arbitrarily) high.

I went over proposed changes. I see a couple small required fixes
(resetting the name to NULL seems to be missing and I think
dup_vma_anon_name needs some tweaking) but overall quite
straight-forward. I'll post a separate patch to do this refactoring.
The original patch is fixing the UAF issue, so I don't want to mix it
with refactoring. Please let me know if you see an issue with
separating it that way.
Thanks,
Suren.


> --
> Michal Hocko
> SUSE Labs