Re: [PATCH v1 6/6] drm/panel: Add Hitachi TX10D07VM0BAA and LG LH400WV3-SD04 MIPI DBI panel driver

[sashiko-bot@kernel.org]

Thank you for your contribution! Sashiko AI review found 2 potential issue(s) to consider:
- [High] drm/panel: missing put_device() causes refcount leak in panel_dbi_prepare()
- [High] drm/panel: unsafe lockless access to remote drvdata risks UAF
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commit af85d3c58c7325c679bd0289254561bdca27049a
Author: Svyatoslav Ryhel <clamor95@gmail.com>

drm/panel: Add Hitachi TX10D07VM0BAA and LG LH400WV3-SD04 MIPI DBI panel driver

This commit adds a DRM panel driver for the Hitachi TX10D07VM0BAA and LG
LH400WV3-SD04 MIPI DBI panels used in the LG Optimus 2X P990. These panels are
linked to the DRM encoder via an RGB to DBI bridge.

> diff --git a/drivers/gpu/drm/panel/panel-hitachi-tx10d07vm0baa.c b/drivers/gpu/drm/panel/panel-hitachi-tx10d07vm0baa.c
> new file mode 100644
> index 0000000000000..e78814c9697af
> --- /dev/null
> +++ b/drivers/gpu/drm/panel/panel-hitachi-tx10d07vm0baa.c
[ ... ]
> +static int panel_dbi_prepare(struct drm_panel *panel)
> +{
> +	struct panel_dbi *priv = to_panel_dbi(panel);
> +	struct platform_device *bridge_pdev;
> +	struct device_node *bridge_node;
> +	struct device *dev = panel->dev;
> +	int ret;
> +
> +	bridge_node = of_graph_get_remote_node(dev_of_node(dev), 0, 0);
> +	if (!bridge_node)
> +		return -ENODEV;
> +
> +	bridge_pdev = of_find_device_by_node(bridge_node);
> +	of_node_put(bridge_node);
> +	if (!bridge_pdev)
> +		return -ENODEV;

[Severity: High]
Does this code leak the reference to bridge_pdev?

The function of_find_device_by_node() increments the reference count of the
returned platform device, but it doesn't appear to be released with
put_device() anywhere in this function. 

Since panel_dbi_prepare() is called on every display enable operation (such as
during a DPMS on/off cycle), couldn't this leak references incrementally and
eventually lead to a refcount overflow or memory exhaustion?

> +
> +	priv->dbi = platform_get_drvdata(bridge_pdev);

[Severity: High]
Is it safe to cache the remote bridge device's drvdata locklessly here?

If the bridge device gets unbound via sysfs while the panel is still active,
the bridge's devres-managed memory would be freed. A subsequent panel
operation, such as calling panel_dbi_command() during teardown, would then
dereference the freed pointer:

    ret = mipi_dbi_command_stackbuf((priv)->dbi, cmd, d, ARRAY_SIZE(d));

Could this lead to a use-after-free, since there is no device link or locking
holding a reference to the bridge's lifecycle?

> +	if (!priv->dbi)
> +		return -ENODEV;
> +
> +	gpiod_set_value_cansleep(priv->reset_gpio, 1);
[ ... ]

-- 
Sashiko AI review · https://sashiko.dev/#/patchset/20260930070535.47130-1-clamor95@gmail.com?part=6