Re: [PATCH v5 02/16] device property: Add fwnode_graph_get_next_port_endpoint()

[sashiko-bot@kernel.org]

Thank you for your contribution! Sashiko AI review found 3 potential issue(s) to consider:

New issues:
- [High] The new `fwnode_graph_get_next_port_endpoint()` helper breaks the `fwnode` graph abstraction by hardcoding OF-specific naming conventions, which will silently ignore valid ACPI and software node endpoints.
- [Medium] `fwnode_graph_get_next_port_endpoint()` fails to unconditionally put the `prev` fwnode reference if an invalid `port` is provided, violating its documented API contract.

Pre-existing issues:
- [High] This problem wasn't introduced by this patch, but iterating over endpoints using `fwnode_get_next_child_node()` causes an infinite loop and Use-After-Free when a device has secondary fwnodes attached.
--

--- Patch [2]: [PATCH v5 02/16] device property: Add fwnode_graph_get_next_port_endpoint() ---
commit 8a16a51eeb8e99439d5b85ce61789ff1153e9060
Author: Chen-Yu Tsai <wenst@chromium.org>

device property: Add fwnode_graph_get_next_port_endpoint()

Adds a helper function to iterate through the endpoint firmware nodes
under a given port. This is intended to be used in USB power sequencing
integration to verify graph connections and supported connector types.

> diff --git a/drivers/base/property.c b/drivers/base/property.c
> index 0bd45f8b01c14..62c6221d65d05 100644
> --- a/drivers/base/property.c
> +++ b/drivers/base/property.c

[ ... ]

> @@ -1099,6 +1099,31 @@ int fwnode_irq_get_byname(const struct fwnode_handle *fwnode, const char *name)
>  }
>  EXPORT_SYMBOL(fwnode_irq_get_byname);
>  
> +/**
> + * fwnode_graph_get_next_port_endpoint - Get next endpoint firmware node in port
> + * @port: Pointer to the target port firmware node
> + * @prev: Previous endpoint node or %NULL to get the first
> + *
> + * The caller is responsible for calling fwnode_handle_put() on the returned
> + * fwnode pointer. Note that this function also puts a reference to @prev
> + * unconditionally.
> + *
> + * Return: an endpoint firmware node pointer or %NULL if no more endpoints
> + * are available.
> + */
> +struct fwnode_handle *fwnode_graph_get_next_port_endpoint(const struct fwnode_handle *port,
> +							  struct fwnode_handle *prev)
> +{
> +	do {
> +		prev = fwnode_get_next_child_node(port, prev);

[Severity: High]
This is a pre-existing issue, but iterating over endpoints using
fwnode_get_next_child_node() can cause an infinite loop and a use-after-free
if a device has secondary fwnodes attached.

If a device port has both primary children and a secondary fwnode, the primary
ops finish and drop the reference to the last primary child, returning NULL.
Then, fwnode_get_next_child_node() incorrectly passes this same dropped child
pointer to the secondary ops:

drivers/base/property.c:fwnode_get_next_child_node() {
	/* Try to find a child in primary fwnode */
	next = fwnode_call_ptr_op(fwnode, get_next_child_node, child);
	if (next)
		return next;

	/* When no more children in primary, continue with secondary */
	return fwnode_call_ptr_op(fwnode->secondary, get_next_child_node, child);
}

This can result in a double-put. Furthermore, when traversing secondary
children, the primary ops don't recognize the software node, treat it as NULL,
and return the first primary child again, creating an infinite loop.

[Severity: Medium]
Does this fail to unconditionally put the prev reference if the provided port
is invalid?

If a caller passes a valid prev node but port is NULL or an error pointer,
fwnode_get_next_child_node() returns early without dropping prev:

drivers/base/property.c:fwnode_get_next_child_node() {
	struct fwnode_handle *next;

	if (IS_ERR_OR_NULL(fwnode))
		return NULL;
    ...
}

Could this lead to a reference count leak, violating the documented API
contract that prev is unconditionally put?

> +		if (fwnode_name_eq(prev, "endpoint"))

[Severity: High]
Does hardcoding this string match break the fwnode graph abstraction for
non-DeviceTree platforms?

By strictly matching the "endpoint" prefix, this bypasses the provider-specific
fwnode_operations, which could silently ignore valid ACPI and software node
endpoints that don't follow this exact naming scheme. Shouldn't this rely on
the backend-specific graph_get_next_endpoint operations instead?

> +			break;
> +	} while (prev);
> +
> +	return prev;
> +}
> +EXPORT_SYMBOL_GPL(fwnode_graph_get_next_port_endpoint);

-- 
Sashiko AI review · https://sashiko.dev/#/patchset/20260715085348.3457359-1-wenst@chromium.org?part=2