[PATCH 6/9] BSS: Verify the ML common info for links

[Jouni Malinen]

On Wed, Jun 18, 2025 at 02:35:28PM +0200, Benjamin Berg wrote:
> Add a check that the AP MLD ADDR, the link ID, the MLD Capabilities and
> Operations the Extended MLD Capabilities as well as the EML Capabilities
> match between links.
> If this is not the case, then refuse to use the offending link.

> diff --git a/wpa_supplicant/bss.c b/wpa_supplicant/bss.c

> +		if (bss->mld_capa != neigh_bss->mld_capa) {
> +			wpa_dbg(wpa_s, MSG_DEBUG,
> +				"MLD: neighbors MLD Capabilities are not matching");
> +			continue;
> +		}
> +
> +		if (bss->eml_capa != neigh_bss->eml_capa) {
> +			wpa_dbg(wpa_s, MSG_DEBUG,
> +				"MLD: neighbors EML Capabilities are not matching");
> +			continue;
> +		}

These are excessive checks since there are reserved bits in those fields
and it does not seem reasonable to mandate reserved, i.e., currently
undefined, bits to have any particular value. The receiver is expected
to discard those reserved bits completely.

> +		/*
> +		 * Check well-defined values in Extended MLD Capabilities.
> +		 * In particular the Recommended Max Simultaneous Links
> +		 * subfield may change over time and is reserved depending on
> +		 * the frame that it is carried in.

This one on the other hand is already addressing such concerns and even
doing that for some of the defined bits.

-- 
Jouni Malinen                                            PGP id EFC895FA