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Subject: Re: [PATCH] userfaultfd_release: always remove uffd flags and clear
 vm_userfaultfd_ctx
To:     Oleg Nesterov <oleg@redhat.com>
CC:     linux-mm <linux-mm@kvack.org>,
        Andrea Arcangeli <aarcange@redhat.com>,
        Peter Xu <peterx@redhat.com>,
        Mike Rapoport <rppt@linux.ibm.com>,
        Jann Horn <jannh@google.com>,
        Jason Gunthorpe <jgg@mellanox.com>,
        Michal Hocko <mhocko@suse.com>,
        Andrew Morton <akpm@linux-foundation.org>,
        Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp>,
        <linux-kernel@vger.kernel.org>
References: <d4583416-5e4a-95e7-a08a-32bf2c9a95fb@huawei.com>
 <20190820160237.GB4983@redhat.com>
From:   Kefeng Wang <wangkefeng.wang@huawei.com>
Message-ID: <d2bf0b99-2cdd-7868-e5ad-8c2cad4681c2@huawei.com>
Date:   Wed, 21 Aug 2019 08:53:17 +0800
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On 2019/8/21 0:02, Oleg Nesterov wrote:
> userfaultfd_release() should clear vm_flags/vm_userfaultfd_ctx even
> if mm->core_state != NULL.
>
> Otherwise a page fault can see userfaultfd_missing() == T and use an
> already freed userfaultfd_ctx.
>
> Reported-by: Kefeng Wang <wangkefeng.wang@huawei.com>
> Fixes: 04f5866e41fb ("coredump: fix race condition between mmget_not_zero()/get_task_mm() and core dumping")
> Cc: stable@vger.kernel.org
> Signed-off-by: Oleg Nesterov <oleg@redhat.com>
> ---
>  fs/userfaultfd.c | 25 +++++++++++++------------
>  1 file changed, 13 insertions(+), 12 deletions(-)

Tested on lts4.4 and 5.3-rc4, Thanks.