Re: [PATCH v11 02/21] drm/bridge: synopsys: dw-dp: Fix incorrect resource lifetimes in bind callback

[sashiko-bot@kernel.org]

Thank you for your contribution! Sashiko AI review found 1 potential issue(s) to consider:
- [High] Use-After-Free and -EBUSY on re-bind due to missing drm_bridge_detach in component unbind.
--

--- Patch [2]: [PATCH v11 02/21] drm/bridge: synopsys: dw-dp: Fix incorrect resource lifetimes in bind callback ---
commit 8317a23524c759645b1aec330e9a401578a81a81
Author: Sebastian Reichel <sebastian.reichel@collabora.com>

drm/bridge: synopsys: dw-dp: Fix incorrect resource lifetimes in bind callback

This commit moves the bridge allocation and resource requests from the bind
callback to the probe callback using a new dw_dp_probe() helper. It also
disables the IRQ in the detach callback to prevent spurious interrupts.

Reported-by: Sashiko <sashiko-bot@kernel.org>

> diff --git a/drivers/gpu/drm/bridge/synopsys/dw-dp.c b/drivers/gpu/drm/bridge/synopsys/dw-dp.c
> index 60feb3d1e14bb..d7945f7fe9f05 100644
> --- a/drivers/gpu/drm/bridge/synopsys/dw-dp.c
> +++ b/drivers/gpu/drm/bridge/synopsys/dw-dp.c

[ ... ]

> @@ -1982,6 +1988,18 @@ static const struct regmap_config dw_dp_regmap_config = {
>  	.rd_table = &dw_dp_readable_table,
>  };
>  
> +int dw_dp_bind(struct dw_dp *dp, struct drm_encoder *encoder)
> +{
> +	return drm_bridge_attach(encoder, &dp->bridge, NULL, DRM_BRIDGE_ATTACH_NO_CONNECTOR);
> +}
> +EXPORT_SYMBOL_GPL(dw_dp_bind);
> +
> +void dw_dp_unbind(struct dw_dp *dp)
> +{
> +	/* nothing to do as bridge is detached automatically */
> +}
> +EXPORT_SYMBOL_GPL(dw_dp_unbind);

[Severity: High]
Since the bridge allocation was moved to probe using devm, the bridge
structure now outlives the component bind/unbind cycle. If the bridge is
not explicitly detached here, does this cause issues during re-bind?

Specifically, if we unbind and re-bind the component, won't
drm_bridge_attach() in dw_dp_bind() return -EBUSY because the bridge is
still attached to the old encoder?

Additionally, can this cause a use-after-free on driver removal? If the
platform driver is removed while a DRM file descriptor is kept open, devm
will free the dp structure. When the file descriptor is eventually closed,
DRM core will call dw_dp_bridge_detach():

static void dw_dp_bridge_detach(struct drm_bridge *bridge)
{
	struct dw_dp *dp = bridge_to_dp(bridge);

	disable_irq(dp->irq);
	cancel_work_sync(&dp->hpd_work);
	...
}

Since dp was already freed by devm, will accessing dp->irq and dp->hpd_work
here crash? Should this unbind function explicitly call drm_bridge_detach()
to prevent both the re-bind failure and the use-after-free?

-- 
Sashiko AI review · https://sashiko.dev/#/patchset/20260806-synopsys-dw-dp-improvements-v11-0-0d508505f383@collabora.com?part=2