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From: Martin Blumenstingl <martin.blumenstingl@googlemail.com>
To: Jiajun Cao <jjcao20@fudan.edu.cn>
Cc: yuanxzhang@fudan.edu.cn, Xin Tan <tanxin.ctf@gmail.com>,
	Neil Armstrong <narmstrong@baylibre.com>,
	David Airlie <airlied@linux.ie>, Daniel Vetter <daniel@ffwll.ch>,
	Kevin Hilman <khilman@baylibre.com>,
	Jerome Brunet <jbrunet@baylibre.com>,
	dri-devel@lists.freedesktop.org,
	linux-amlogic@lists.infradead.org,
	linux-arm-kernel@lists.infradead.org,
	linux-kernel@vger.kernel.org
Subject: Re: [PATCH v2] drm/meson: fix potential NULL pointer exception in meson_drv_unbind()
Date: Thu, 1 Jul 2021 23:34:37 +0200	[thread overview]
Message-ID: <CAFBinCCGpbCNOcbgCZcLa1O8mJd0wgLtt4_sAMvwQW4xOxkuWg@mail.gmail.com> (raw)
In-Reply-To: <20210618052800.89007-1-jjcao20@fudan.edu.cn>

Hello,

first of all: thanks for your patch and sorry for being late with my
review question.

On Fri, Jun 18, 2021 at 7:28 AM Jiajun Cao <jjcao20@fudan.edu.cn> wrote:
>
> Fix a potential NULL pointer exception when meson_drv_unbind()
> attempts to operate on the driver_data priv which may be NULL.
> Add a null pointer check on the priv struct to avoid the NULL
> pointer dereference after calling dev_get_drvdata(), just like
> the null pointer checks done on the struct priv in the function
> meson_drv_shutdown(), meson_drv_pm_suspend() and meson_drv_pm_resume().
I am trying to review Amlogic Meson related patches in the DRM
subsystem so I can help Neil with this.
However, I am still new to this so please help me educate on this topic.

[...]
>  static void meson_drv_unbind(struct device *dev)
>  {
>         struct meson_drm *priv = dev_get_drvdata(dev);
> -       struct drm_device *drm = priv->drm;
> +       struct drm_device *drm;
> +
> +       if (!priv)
> +               return;
My understanding of the component framework is that meson_drv_unbind()
is only called if previously meson_drv_bind() was called (and did not
return any error).
This is different from meson_drv_shutdown() (for example) because that
can be called if meson_drv_probe() returns 0 (success) in case the
"count" variable was 0 (then the probe function does nothing).

As I mentioned before: I am still learning about the DRM subsystem in
the Linux kernel.
So it would be great if you could help me understand for which
scenarios this newly added if-condition is needed.


Thank you!
Best regards,
Martin

WARNING: multiple messages have this Message-ID (diff)
From: Martin Blumenstingl <martin.blumenstingl@googlemail.com>
To: Jiajun Cao <jjcao20@fudan.edu.cn>
Cc: yuanxzhang@fudan.edu.cn, Xin Tan <tanxin.ctf@gmail.com>,
	 Neil Armstrong <narmstrong@baylibre.com>,
	David Airlie <airlied@linux.ie>,  Daniel Vetter <daniel@ffwll.ch>,
	Kevin Hilman <khilman@baylibre.com>,
	 Jerome Brunet <jbrunet@baylibre.com>,
	dri-devel@lists.freedesktop.org,
	 linux-amlogic@lists.infradead.org,
	linux-arm-kernel@lists.infradead.org,
	 linux-kernel@vger.kernel.org
Subject: Re: [PATCH v2] drm/meson: fix potential NULL pointer exception in meson_drv_unbind()
Date: Thu, 1 Jul 2021 23:34:37 +0200	[thread overview]
Message-ID: <CAFBinCCGpbCNOcbgCZcLa1O8mJd0wgLtt4_sAMvwQW4xOxkuWg@mail.gmail.com> (raw)
In-Reply-To: <20210618052800.89007-1-jjcao20@fudan.edu.cn>

Hello,

first of all: thanks for your patch and sorry for being late with my
review question.

On Fri, Jun 18, 2021 at 7:28 AM Jiajun Cao <jjcao20@fudan.edu.cn> wrote:
>
> Fix a potential NULL pointer exception when meson_drv_unbind()
> attempts to operate on the driver_data priv which may be NULL.
> Add a null pointer check on the priv struct to avoid the NULL
> pointer dereference after calling dev_get_drvdata(), just like
> the null pointer checks done on the struct priv in the function
> meson_drv_shutdown(), meson_drv_pm_suspend() and meson_drv_pm_resume().
I am trying to review Amlogic Meson related patches in the DRM
subsystem so I can help Neil with this.
However, I am still new to this so please help me educate on this topic.

[...]
>  static void meson_drv_unbind(struct device *dev)
>  {
>         struct meson_drm *priv = dev_get_drvdata(dev);
> -       struct drm_device *drm = priv->drm;
> +       struct drm_device *drm;
> +
> +       if (!priv)
> +               return;
My understanding of the component framework is that meson_drv_unbind()
is only called if previously meson_drv_bind() was called (and did not
return any error).
This is different from meson_drv_shutdown() (for example) because that
can be called if meson_drv_probe() returns 0 (success) in case the
"count" variable was 0 (then the probe function does nothing).

As I mentioned before: I am still learning about the DRM subsystem in
the Linux kernel.
So it would be great if you could help me understand for which
scenarios this newly added if-condition is needed.


Thank you!
Best regards,
Martin

_______________________________________________
linux-arm-kernel mailing list
linux-arm-kernel@lists.infradead.org
http://lists.infradead.org/mailman/listinfo/linux-arm-kernel

WARNING: multiple messages have this Message-ID (diff)
From: Martin Blumenstingl <martin.blumenstingl@googlemail.com>
To: Jiajun Cao <jjcao20@fudan.edu.cn>
Cc: Xin Tan <tanxin.ctf@gmail.com>,
	Neil Armstrong <narmstrong@baylibre.com>,
	David Airlie <airlied@linux.ie>,
	Kevin Hilman <khilman@baylibre.com>,
	yuanxzhang@fudan.edu.cn, linux-kernel@vger.kernel.org,
	dri-devel@lists.freedesktop.org,
	linux-amlogic@lists.infradead.org,
	linux-arm-kernel@lists.infradead.org,
	Jerome Brunet <jbrunet@baylibre.com>
Subject: Re: [PATCH v2] drm/meson: fix potential NULL pointer exception in meson_drv_unbind()
Date: Thu, 1 Jul 2021 23:34:37 +0200	[thread overview]
Message-ID: <CAFBinCCGpbCNOcbgCZcLa1O8mJd0wgLtt4_sAMvwQW4xOxkuWg@mail.gmail.com> (raw)
In-Reply-To: <20210618052800.89007-1-jjcao20@fudan.edu.cn>

Hello,

first of all: thanks for your patch and sorry for being late with my
review question.

On Fri, Jun 18, 2021 at 7:28 AM Jiajun Cao <jjcao20@fudan.edu.cn> wrote:
>
> Fix a potential NULL pointer exception when meson_drv_unbind()
> attempts to operate on the driver_data priv which may be NULL.
> Add a null pointer check on the priv struct to avoid the NULL
> pointer dereference after calling dev_get_drvdata(), just like
> the null pointer checks done on the struct priv in the function
> meson_drv_shutdown(), meson_drv_pm_suspend() and meson_drv_pm_resume().
I am trying to review Amlogic Meson related patches in the DRM
subsystem so I can help Neil with this.
However, I am still new to this so please help me educate on this topic.

[...]
>  static void meson_drv_unbind(struct device *dev)
>  {
>         struct meson_drm *priv = dev_get_drvdata(dev);
> -       struct drm_device *drm = priv->drm;
> +       struct drm_device *drm;
> +
> +       if (!priv)
> +               return;
My understanding of the component framework is that meson_drv_unbind()
is only called if previously meson_drv_bind() was called (and did not
return any error).
This is different from meson_drv_shutdown() (for example) because that
can be called if meson_drv_probe() returns 0 (success) in case the
"count" variable was 0 (then the probe function does nothing).

As I mentioned before: I am still learning about the DRM subsystem in
the Linux kernel.
So it would be great if you could help me understand for which
scenarios this newly added if-condition is needed.


Thank you!
Best regards,
Martin

WARNING: multiple messages have this Message-ID (diff)
From: Martin Blumenstingl <martin.blumenstingl@googlemail.com>
To: Jiajun Cao <jjcao20@fudan.edu.cn>
Cc: yuanxzhang@fudan.edu.cn, Xin Tan <tanxin.ctf@gmail.com>,
	 Neil Armstrong <narmstrong@baylibre.com>,
	David Airlie <airlied@linux.ie>,  Daniel Vetter <daniel@ffwll.ch>,
	Kevin Hilman <khilman@baylibre.com>,
	 Jerome Brunet <jbrunet@baylibre.com>,
	dri-devel@lists.freedesktop.org,
	 linux-amlogic@lists.infradead.org,
	linux-arm-kernel@lists.infradead.org,
	 linux-kernel@vger.kernel.org
Subject: Re: [PATCH v2] drm/meson: fix potential NULL pointer exception in meson_drv_unbind()
Date: Thu, 1 Jul 2021 23:34:37 +0200	[thread overview]
Message-ID: <CAFBinCCGpbCNOcbgCZcLa1O8mJd0wgLtt4_sAMvwQW4xOxkuWg@mail.gmail.com> (raw)
In-Reply-To: <20210618052800.89007-1-jjcao20@fudan.edu.cn>

Hello,

first of all: thanks for your patch and sorry for being late with my
review question.

On Fri, Jun 18, 2021 at 7:28 AM Jiajun Cao <jjcao20@fudan.edu.cn> wrote:
>
> Fix a potential NULL pointer exception when meson_drv_unbind()
> attempts to operate on the driver_data priv which may be NULL.
> Add a null pointer check on the priv struct to avoid the NULL
> pointer dereference after calling dev_get_drvdata(), just like
> the null pointer checks done on the struct priv in the function
> meson_drv_shutdown(), meson_drv_pm_suspend() and meson_drv_pm_resume().
I am trying to review Amlogic Meson related patches in the DRM
subsystem so I can help Neil with this.
However, I am still new to this so please help me educate on this topic.

[...]
>  static void meson_drv_unbind(struct device *dev)
>  {
>         struct meson_drm *priv = dev_get_drvdata(dev);
> -       struct drm_device *drm = priv->drm;
> +       struct drm_device *drm;
> +
> +       if (!priv)
> +               return;
My understanding of the component framework is that meson_drv_unbind()
is only called if previously meson_drv_bind() was called (and did not
return any error).
This is different from meson_drv_shutdown() (for example) because that
can be called if meson_drv_probe() returns 0 (success) in case the
"count" variable was 0 (then the probe function does nothing).

As I mentioned before: I am still learning about the DRM subsystem in
the Linux kernel.
So it would be great if you could help me understand for which
scenarios this newly added if-condition is needed.


Thank you!
Best regards,
Martin

_______________________________________________
linux-amlogic mailing list
linux-amlogic@lists.infradead.org
http://lists.infradead.org/mailman/listinfo/linux-amlogic

  reply	other threads:[~2021-07-01 21:34 UTC|newest]

Thread overview: 8+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-06-18  5:28 [PATCH v2] drm/meson: fix potential NULL pointer exception in meson_drv_unbind() Jiajun Cao
2021-06-18  5:28 ` Jiajun Cao
2021-06-18  5:28 ` Jiajun Cao
2021-06-18  5:28 ` Jiajun Cao
2021-07-01 21:34 ` Martin Blumenstingl [this message]
2021-07-01 21:34   ` Martin Blumenstingl
2021-07-01 21:34   ` Martin Blumenstingl
2021-07-01 21:34   ` Martin Blumenstingl

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