linux-kernel - Re: [PATCH v2] drm/bridge: megachips: Fix a null pointer dereference bug

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Date:   Tue, 30 Aug 2022 10:11:01 +0200
From:   Robert Foss <robert.foss@...aro.org>
To:     Zheyu Ma <zheyuma97@...il.com>
Cc:     peter.senna@...il.com, martin.donnelly@...com,
        martyn.welch@...labora.co.uk, andrzej.hajda@...el.com,
        narmstrong@...libre.com, Laurent.pinchart@...asonboard.com,
        jonas@...boo.se, jernej.skrabec@...il.com, airlied@...ux.ie,
        daniel@...ll.ch, dri-devel@...ts.freedesktop.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2] drm/bridge: megachips: Fix a null pointer dereference bug

On Tue, 30 Aug 2022 at 09:35, Zheyu Ma <zheyuma97@...il.com> 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.
>
> Fixes: 11632d4aa2b3 ("drm/bridge: megachips: Ensure both bridges are probed before registration")
> Signed-off-by: Zheyu Ma <zheyuma97@...il.com>
> ---
> Changes in v2:
>     - Alignment format
> ---
>  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..72248a565579 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);
> --
> 2.25.1
>

Applied to drm-misc-next.