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References: <20210907122633.16665-1-cymi20@fudan.edu.cn>
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From:   Karol Herbst <kherbst@redhat.com>
Date:   Tue, 5 Oct 2021 23:27:20 +0200
Message-ID: <CACO55tvUuZJD_AOgxS=Ts3MBhXkJARwWapF6QaxQqTk0JG7zWQ@mail.gmail.com>
Subject: Re: [PATCH] drm/nouveau/svm: Fix refcount leak bug and missing check
 against null bug
To:     Chenyuan Mi <cymi20@fudan.edu.cn>
Cc:     yuanxzhang@fudan.edu.cn, Xiyu Yang <xiyuyang19@fudan.edu.cn>,
        Xin Tan <tanxin.ctf@gmail.com>,
        Ben Skeggs <bskeggs@redhat.com>,
        David Airlie <airlied@linux.ie>,
        Daniel Vetter <daniel@ffwll.ch>,
        dri-devel <dri-devel@lists.freedesktop.org>,
        nouveau <nouveau@lists.freedesktop.org>,
        LKML <linux-kernel@vger.kernel.org>
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I think it makes sense to add a Fixes tag to this:

Fixes: 822cab6150d3 ("drm/nouveau/svm: check for SVM initialized
before migrating")
Reviewed-by: Karol Herbst <kherbst@redhat.com>

On Tue, Sep 7, 2021 at 3:20 PM Chenyuan Mi <cymi20@fudan.edu.cn> wrote:
>
> The reference counting issue happens in one exception handling path of
> nouveau_svmm_bind(). When cli->svm.svmm is null, the function forgets
> to decrease the refcount of mm increased by get_task_mm(), causing a
> refcount leak.
>
> Fix this issue by using mmput() to decrease the refcount in the
> exception handling path.
>
> Also, the function forgets to do check against null when get mm
> by get_task_mm().
>
> Fix this issue by adding null check after get mm by get_task_mm().
>
> Signed-off-by: Chenyuan Mi <cymi20@fudan.edu.cn>
> Signed-off-by: Xiyu Yang <xiyuyang19@fudan.edu.cn>
> Signed-off-by: Xin Tan <tanxin.ctf@gmail.com>
> ---
>  drivers/gpu/drm/nouveau/nouveau_svm.c | 4 ++++
>  1 file changed, 4 insertions(+)
>
> diff --git a/drivers/gpu/drm/nouveau/nouveau_svm.c b/drivers/gpu/drm/nouveau/nouveau_svm.c
> index b0c3422cb01f..9985bfde015a 100644
> --- a/drivers/gpu/drm/nouveau/nouveau_svm.c
> +++ b/drivers/gpu/drm/nouveau/nouveau_svm.c
> @@ -162,10 +162,14 @@ nouveau_svmm_bind(struct drm_device *dev, void *data,
>          */
>
>         mm = get_task_mm(current);
> +       if (!mm) {
> +               return -EINVAL;
> +       }
>         mmap_read_lock(mm);
>
>         if (!cli->svm.svmm) {
>                 mmap_read_unlock(mm);
> +               mmput(mm);
>                 return -EINVAL;
>         }
>
> --
> 2.17.1
>