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From:   Yang Shi <shy828301@gmail.com>
Date:   Tue, 15 Feb 2022 12:42:59 -0800
Message-ID: <CAHbLzkoeCP-ONBNsDB-y63chxWCZejeQKXg6zc2AAQWCixjxQA@mail.gmail.com>
Subject: Re: [PATCH 1/1] mm: fix use-after-free bug when mm->mmap is reused
 after being freed
To:     Suren Baghdasaryan <surenb@google.com>
Cc:     Andrew Morton <akpm@linux-foundation.org>,
        Michal Hocko <mhocko@kernel.org>,
        Michal Hocko <mhocko@suse.com>,
        David Rientjes <rientjes@google.com>,
        Matthew Wilcox <willy@infradead.org>,
        Johannes Weiner <hannes@cmpxchg.org>,
        Roman Gushchin <guro@fb.com>, Rik van Riel <riel@surriel.com>,
        Minchan Kim <minchan@kernel.org>,
        "Kirill A. Shutemov" <kirill@shutemov.name>,
        Andrea Arcangeli <aarcange@redhat.com>, brauner@kernel.org,
        christian@brauner.io, Christoph Hellwig <hch@infradead.org>,
        Oleg Nesterov <oleg@redhat.com>,
        David Hildenbrand <david@redhat.com>,
        Jann Horn <jannh@google.com>,
        Shakeel Butt <shakeelb@google.com>, luto@kernel.org,
        christian.brauner@ubuntu.com, fweimer@redhat.com, jengelh@inai.de,
        timmurray@google.com, Linux MM <linux-mm@kvack.org>,
        Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
        kernel-team@android.com,
        syzbot+2ccf63a4bd07cf39cab0@syzkaller.appspotmail.com
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On Tue, Feb 15, 2022 at 12:19 PM Suren Baghdasaryan <surenb@google.com> wrote:
>
> After exit_mmap frees all vmas in the mm, mm->mmap needs to be reset,
> otherwise it points to a vma that was freed and when reused leads to
> a use-after-free bug.
>
> Reported-by: syzbot+2ccf63a4bd07cf39cab0@syzkaller.appspotmail.com
> Suggested-by: Michal Hocko <mhocko@suse.com>
> Signed-off-by: Suren Baghdasaryan <surenb@google.com>

Looks good to me. Reviewed-by: Yang Shi <shy828301@gmail.com>

> ---
>  mm/mmap.c | 1 +
>  1 file changed, 1 insertion(+)
>
> diff --git a/mm/mmap.c b/mm/mmap.c
> index 1e8fdb0b51ed..d445c1b9d606 100644
> --- a/mm/mmap.c
> +++ b/mm/mmap.c
> @@ -3186,6 +3186,7 @@ void exit_mmap(struct mm_struct *mm)
>                 vma = remove_vma(vma);
>                 cond_resched();
>         }
> +       mm->mmap = NULL;
>         mmap_write_unlock(mm);
>         vm_unacct_memory(nr_accounted);
>  }
> --
> 2.35.1.265.g69c8d7142f-goog
>