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Date:   Tue, 2 Aug 2022 15:04:04 +0300
From:   Ian Ray <ian.ray@ge.com>
To:     Martyn Welch <martyn.welch@collabora.co.uk>
Cc:     Zheyu Ma <zheyuma97@gmail.com>, peter.senna@gmail.com,
        andrzej.hajda@intel.com, narmstrong@baylibre.com,
        robert.foss@linaro.org, Laurent.pinchart@ideasonboard.com,
        jonas@kwiboo.se, jernej.skrabec@gmail.com, airlied@linux.ie,
        daniel@ffwll.ch, dri-devel@lists.freedesktop.org,
        linux-kernel@vger.kernel.org
Subject: Re: [PATCH] drm/bridge: megachips: Fix a null pointer dereference bug
Message-ID: <20220802120403.GA26182@zoo6.em.health.ge.com>
References: <20220716081304.2762135-1-zheyuma97@gmail.com>
 <946c008942f4ef4ca642818b23e9941c162383e3.camel@collabora.co.uk>
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On Tue, Jul 19, 2022 at 09:38:16AM +0100, Martyn Welch wrote:
> On Sat, 2022-07-16 at 16:13 +0800, Zheyu Ma wrote:
> > When removing the module we will get the following warning:
> > 
> > [?? 31.911505] i2c-core: driver [stdp2690-ge-b850v3-fw] unregistered
> > [?? 31.912484] general protection fault, probably for non-canonical
> > address 0xdffffc0000000001: 0000 [#1] PREEMPT SMP KASAN PTI
> > [?? 31.913338] KASAN: null-ptr-deref in range [0x0000000000000008-
> > 0x000000000000000f]
> > [?? 31.915280] RIP: 0010:drm_bridge_remove+0x97/0x130
> > [?? 31.921825] Call Trace:
> > [?? 31.922533]? stdp4028_ge_b850v3_fw_remove+0x34/0x60
> > [megachips_stdpxxxx_ge_b850v3_fw]
> > [?? 31.923139]? i2c_device_remove+0x181/0x1f0
> > 
> > The two bridges (stdp2690, stdp4028) do not probe at the same time,
> > so
> > the driver does not call ge_b850v3_resgiter() when probing, causing
> > the
> > driver to try to remove the object that has not been initialized.
> > 
> > Fix this by checking whether both the bridges are probed.
> > 
> > Signed-off-by: Zheyu Ma <zheyuma97@gmail.com>
> 
> Good catch!
> 
> Acked-by: Martyn Welch <martyn.welch@collabora.com>

Tested-by: Ian Ray <ian.ray@ge.com>


> 
> Would be worth adding:
> 
> Fixes: 11632d4aa2b3 ("drm/bridge: megachips: Ensure both bridges are
> probed before registration")
> 
> > ---
> > ?drivers/gpu/drm/bridge/megachips-stdpxxxx-ge-b850v3-fw.c | 4 +++-
> > ?1 file changed, 3 insertions(+), 1 deletion(-)
> > 
> > diff --git a/drivers/gpu/drm/bridge/megachips-stdpxxxx-ge-b850v3-fw.c
> > b/drivers/gpu/drm/bridge/megachips-stdpxxxx-ge-b850v3-fw.c
> > index cce98bf2a4e7..c68a4cdf4625 100644
> > --- a/drivers/gpu/drm/bridge/megachips-stdpxxxx-ge-b850v3-fw.c
> > +++ b/drivers/gpu/drm/bridge/megachips-stdpxxxx-ge-b850v3-fw.c
> > @@ -296,7 +296,9 @@ static void ge_b850v3_lvds_remove(void)
> > ???????? * This check is to avoid both the drivers
> > ???????? * removing the bridge in their remove() function
> > ???????? */
> > -???????if (!ge_b850v3_lvds_ptr)
> > +???????if (!ge_b850v3_lvds_ptr ||
> > +???????????????!ge_b850v3_lvds_ptr->stdp2690_i2c ||
> > +???????????????!ge_b850v3_lvds_ptr->stdp4028_i2c)
> > ????????????????goto out;
> > ?
> > ????????drm_bridge_remove(&ge_b850v3_lvds_ptr->bridge);
>