Re: [PATCH V3 2/4 net-next?] net: dsa: b53: prefer CPU port 8 for Northstar devices

Thank you for your contribution! Sashiko AI review found 1 potential issue(s) to consider:
- [High] Missing NULL pointer check on the result of `dsa_to_port()` before passing it to `dsa_port_is_cpu()`, leading to a potential NULL pointer dereference.
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--- Patch [2]: [PATCH V3 2/4 net-next?] net: dsa: b53: prefer CPU port 8 for Northstar devices ---
commit 2ae0d011f243e38dabfab275559b868d62bf66f6
Author: Rafał Miłecki <[email protected]>

net: dsa: b53: prefer CPU port 8 for Northstar devices

This patch prefers CPU port 8 if available for Northstar devices. Ports
5 and 7 have limitations with CPU trapping features compared to port 8.

> diff --git a/drivers/net/dsa/b53/b53_common.c b/drivers/net/dsa/b53/b53_common.c
> index 5fd8362d04304..052812d2faa93 100644
> --- a/drivers/net/dsa/b53/b53_common.c
> +++ b/drivers/net/dsa/b53/b53_common.c

[ ... ]

> +static struct dsa_port *b53_preferred_default_local_cpu_port(struct dsa_switch *ds)
> +{
> +	struct b53_device *dev = ds->priv;
> +	struct dsa_port *cpu_dp;

[ ... ]

> +	if (is5301x(dev)) {
> +		cpu_dp = dsa_to_port(ds, B53_CPU_PORT);
> +
> +		if (dsa_port_is_cpu(cpu_dp))

[Severity: High]
Does this code risk a NULL pointer dereference during device probe?

If a Northstar SoC is configured without port 8 (for example, in setups
using only port 5 or 7 as the CPU port), dsa_to_port() will return NULL.
The dsa_port_is_cpu() function dereferences the passed port pointer directly:

include/net/dsa.h:dsa_port_is_cpu() {
	return port->type == DSA_PORT_TYPE_CPU;
}

Passing NULL to dsa_port_is_cpu() would cause a panic. Could cpu_dp be
checked for NULL before calling dsa_port_is_cpu()?

> +			return cpu_dp;
> +	}
> +
> +	return NULL;
> +}

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Sashiko AI review · https://sashiko.dev/#/patchset/[email protected]?part=2