wlan_common/

capabilities.rs

// Copyright 2021 The Fuchsia Authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.

//! This module tries to check the iface device's capabilities against the BSS it is instructed to
//! join. The capabilities will be tailored based on the band.
//! Next, rates will be joined with the AP and HT Capabilities and VHT Capabilities may be modified
//! based on the user-overridable join channel and bandwidth.
//! If successful, the capabilities will be extracted and saved.

use crate::channel::{Cbw, Channel};
use crate::ie::intersect::*;
use crate::ie::{
    self, HtCapabilities, SupportedRate, VhtCapabilities, parse_ht_capabilities,
    parse_vht_capabilities,
};
use crate::mac::CapabilityInfo;
use anyhow::{Context as _, Error, format_err};
use fidl_fuchsia_wlan_ieee80211 as fidl_ieee80211;
use fidl_fuchsia_wlan_mlme as fidl_mlme;

/// Capability Info is defined in IEEE Std 802.11-1026 9.4.1.4.
/// Figure 9-68 indicates BSS and IBSS bits are reserved for client.
/// However, some APs will reject association unless they are set to true and false, respectively.
const OVERRIDE_CAP_INFO_ESS: bool = true;
const OVERRIDE_CAP_INFO_IBSS: bool = false;

/// IEEE Std 802.11-2016 Table 9-43 defines CF-Pollable and CF-Poll Request, Fuchsia does not
/// support them.
const OVERRIDE_CAP_INFO_CF_POLLABLE: bool = false;
const OVERRIDE_CAP_INFO_CF_POLL_REQUEST: bool = false;

/// In an RSNA non-AP STA, privacy bit is set to false. Otherwise it is reserved (has no meaning and
/// is not used).
const OVERRIDE_CAP_INFO_PRIVACY: bool = false;

/// Spectrum Management bit indicates dot11SpectrumManagementRequired. Fuchsia does not support it.
const OVERRIDE_CAP_INFO_SPECTRUM_MGMT: bool = false;

/// Fuchsia does not support tx_stbc with our existing SoftMAC chips.
const OVERRIDE_HT_CAP_INFO_TX_STBC: bool = false;

/// Supported channel bandwidth set can only be non-zero if the associating channel is 160 MHz or
/// 80+80 MHz Channel bandwidth. Otherwise it will be set to 0. 0 is a purely numeric value without
/// a name. See IEEE Std 802.11-2016 Table 9-250 for more details.
/// TODO(https://fxbug.dev/42115418): finer control over CBW if necessary.
const OVERRIDE_VHT_CAP_INFO_SUPPORTED_CBW_SET: u32 = 0;

/// A driver may not properly populate an interface's Capabilities to reflect the selected role.
/// Override the reported capabilities to ensure compatibility with Client role.
fn override_capability_info(capability_info: CapabilityInfo) -> CapabilityInfo {
    capability_info
        .with_ess(OVERRIDE_CAP_INFO_ESS)
        .with_ibss(OVERRIDE_CAP_INFO_IBSS)
        .with_cf_pollable(OVERRIDE_CAP_INFO_CF_POLLABLE)
        .with_cf_poll_req(OVERRIDE_CAP_INFO_CF_POLL_REQUEST)
        .with_privacy(OVERRIDE_CAP_INFO_PRIVACY)
        .with_spectrum_mgmt(OVERRIDE_CAP_INFO_SPECTRUM_MGMT)
}

/// The entry point of this module.
/// 1. Extract the band capabilities from the iface device based on BSS channel.
/// 2. Derive/Override capabilities based on iface capabilities, BSS requirements and
/// user overridable channel bandwidths.
pub fn derive_join_capabilities(
    bss_channel: Channel,
    bss_rates: &[SupportedRate],
    device_info: &fidl_mlme::DeviceInfo,
) -> Result<ClientCapabilities, Error> {
    // Step 1 - Extract iface capabilities for this particular band we are joining
    let band_cap = get_band_cap_for_channel(&device_info.bands[..], bss_channel)
        .context(format!("iface does not support BSS channel {}", bss_channel.primary))?;

    // Step 2.1 - Override CapabilityInfo
    // TODO(https://fxbug.dev/42132496): The WlanSoftmacHardwareCapability type is u32 and used here to override
    // the capability info for joining a BSS. The upper bits are removed but shouldn't have to be.
    let capability_info =
        override_capability_info(CapabilityInfo(device_info.softmac_hardware_capability as u16));

    // Step 2.2 - Derive data rates
    // Both are safe to unwrap because SupportedRate is one byte and will not cause alignment issue.
    let client_rates = band_cap.basic_rates.iter().map(|&r| SupportedRate(r)).collect::<Vec<_>>();
    let rates = intersect_rates(ApRates(bss_rates), ClientRates(&client_rates))
        .map_err(|error| format_err!("could not intersect rates: {:?}", error))
        .context(format!("deriving rates: {:?} + {:?}", band_cap.basic_rates, bss_rates))?;

    // Step 2.3 - Override HT Capabilities and VHT Capabilities
    // Here it is assumed that the channel specified by the BSS will never be invalid.
    let (ht_cap, vht_cap) =
        override_ht_vht(band_cap.ht_cap.as_ref(), band_cap.vht_cap.as_ref(), bss_channel.cbw)?;

    Ok(ClientCapabilities(StaCapabilities { capability_info, rates, ht_cap, vht_cap }))
}

/// Wrapper function to convert FIDL {HT,VHT}Capabilities into byte arrays, taking into account the
/// limitations imposed by the channel bandwidth.
fn override_ht_vht(
    fidl_ht_cap: Option<&Box<fidl_ieee80211::HtCapabilities>>,
    fidl_vht_cap: Option<&Box<fidl_ieee80211::VhtCapabilities>>,
    cbw: Cbw,
) -> Result<(Option<HtCapabilities>, Option<VhtCapabilities>), Error> {
    if fidl_ht_cap.is_none() && fidl_vht_cap.is_some() {
        return Err(format_err!("VHT Cap without HT Cap is invalid."));
    }

    let ht_cap = match fidl_ht_cap {
        Some(h) => {
            let ht_cap = *parse_ht_capabilities(&h.bytes[..]).context("verifying HT Cap")?;
            Some(override_ht_capabilities(ht_cap, cbw))
        }
        None => None,
    };

    let vht_cap = match fidl_vht_cap {
        Some(v) => {
            let vht_cap = *parse_vht_capabilities(&v.bytes[..]).context("verifying VHT Cap")?;
            Some(override_vht_capabilities(vht_cap, cbw))
        }
        None => None,
    };
    Ok((ht_cap, vht_cap))
}

/// Even though hardware may support higher channel bandwidth, if user specifies a narrower
/// bandwidth, change the channel bandwidth in ht_cap_info to match user's preference.
fn override_ht_capabilities(mut ht_cap: HtCapabilities, cbw: Cbw) -> HtCapabilities {
    let mut ht_cap_info = ht_cap.ht_cap_info.with_tx_stbc(OVERRIDE_HT_CAP_INFO_TX_STBC);
    match cbw {
        Cbw::Cbw20 => ht_cap_info.set_chan_width_set(ie::ChanWidthSet::TWENTY_ONLY),
        _ => (),
    }
    ht_cap.ht_cap_info = ht_cap_info;
    ht_cap
}

/// Even though hardware may support higher channel bandwidth, if user specifies a narrower
/// bandwidth, change the channel bandwidth in vht_cap_info to match user's preference.
fn override_vht_capabilities(mut vht_cap: VhtCapabilities, cbw: Cbw) -> VhtCapabilities {
    let mut vht_cap_info = vht_cap.vht_cap_info;
    if vht_cap_info.supported_cbw_set() != OVERRIDE_VHT_CAP_INFO_SUPPORTED_CBW_SET {
        // Supported channel bandwidth set can only be non-zero if the associating channel is
        // 160 MHz or 80+80 MHz Channel bandwidth. Otherwise it will be set to 0. 0 is a purely
        // numeric value without a name. See IEEE Std 802.11-2016 Table 9-250 for more details.
        // TODO(https://fxbug.dev/42115418): finer control over CBW if necessary.
        match cbw {
            Cbw::Cbw160 | Cbw::Cbw80P80 { secondary80: _ } => (),
            _ => vht_cap_info.set_supported_cbw_set(OVERRIDE_VHT_CAP_INFO_SUPPORTED_CBW_SET),
        }
    }
    vht_cap.vht_cap_info = vht_cap_info;
    vht_cap
}

pub fn get_band_cap_for_channel(
    bands: &[fidl_mlme::BandCapability],
    channel: Channel,
) -> Result<&fidl_mlme::BandCapability, anyhow::Error> {
    let target = channel.get_band().context("Failed to retrieve band capabilities")?;
    bands
        .iter()
        .find(|b| {
            b.band == target && b.primary_channels.iter().any(|c| c.number == channel.primary)
        })
        .ok_or_else(|| format_err!("No band capability for channel {channel:?}: {bands:?}"))
}

/// Capabilities that takes the iface device's capabilities based on the channel a client is trying
/// to join, the PHY parameters that is overridden by user's command line input and the BSS the
/// client are is trying to join.
/// They are stored in the form of IEs because at some point they will be transmitted in
/// (Re)Association Request and (Re)Association Response frames.
#[derive(Debug, PartialEq)]
pub struct StaCapabilities {
    pub capability_info: CapabilityInfo,
    pub rates: Vec<SupportedRate>,
    pub ht_cap: Option<HtCapabilities>,
    pub vht_cap: Option<VhtCapabilities>,
}

#[derive(Debug, PartialEq)]
pub struct ClientCapabilities(pub StaCapabilities);
#[derive(Debug, PartialEq)]
pub struct ApCapabilities(pub StaCapabilities);

/// Performs capability negotiation with an AP assuming the Fuchsia device is a client.
pub fn intersect_with_ap_as_client(
    client: &ClientCapabilities,
    ap: &ApCapabilities,
) -> Result<StaCapabilities, Error> {
    let rates = intersect_rates(ApRates(&ap.0.rates[..]), ClientRates(&client.0.rates[..]))
        .map_err(|e| format_err!("could not intersect rates: {:?}", e))?;
    let (capability_info, ht_cap, vht_cap) = intersect(&client.0, &ap.0);
    Ok(StaCapabilities { rates, capability_info, ht_cap, vht_cap })
}

/// Performs capability negotiation with a remote client assuming the Fuchsia device is an AP.
pub fn intersect_with_remote_client_as_ap(
    ap: &ApCapabilities,
    remote_client: &ClientCapabilities,
) -> StaCapabilities {
    // Safe to unwrap. Otherwise we would have rejected the association from this remote client.
    let rates = intersect_rates(ApRates(&ap.0.rates[..]), ClientRates(&remote_client.0.rates[..]))
        .unwrap_or(vec![]);
    let (capability_info, ht_cap, vht_cap) = intersect(&ap.0, &remote_client.0);
    StaCapabilities { rates, capability_info, ht_cap, vht_cap }
}

fn intersect(
    ours: &StaCapabilities,
    theirs: &StaCapabilities,
) -> (CapabilityInfo, Option<HtCapabilities>, Option<VhtCapabilities>) {
    // Every bit is a boolean so bit-wise and is sufficient
    let capability_info = CapabilityInfo(ours.capability_info.raw() & theirs.capability_info.raw());
    let ht_cap = match (ours.ht_cap, theirs.ht_cap) {
        // Intersect is NOT necessarily symmetrical. Our own capabilities prevails.
        (Some(ours), Some(theirs)) => Some(ours.intersect(&theirs)),
        _ => None,
    };
    let vht_cap = match (ours.vht_cap, theirs.vht_cap) {
        // Intersect is NOT necessarily symmetrical. Our own capabilities prevails.
        (Some(ours), Some(theirs)) => Some(ours.intersect(&theirs)),
        _ => None,
    };
    (capability_info, ht_cap, vht_cap)
}

#[cfg(test)]
mod tests {
    use super::*;
    use crate::mac;
    use crate::test_utils::fake_capabilities::fake_5ghz_band_capability_ht;
    use assert_matches::assert_matches;
    use fidl_fuchsia_wlan_common as fidl_common;

    #[test]
    fn test_build_cap_info() {
        let capability_info = CapabilityInfo(0)
            .with_ess(!OVERRIDE_CAP_INFO_ESS)
            .with_ibss(!OVERRIDE_CAP_INFO_IBSS)
            .with_cf_pollable(!OVERRIDE_CAP_INFO_CF_POLLABLE)
            .with_cf_poll_req(!OVERRIDE_CAP_INFO_CF_POLL_REQUEST)
            .with_privacy(!OVERRIDE_CAP_INFO_PRIVACY)
            .with_spectrum_mgmt(!OVERRIDE_CAP_INFO_SPECTRUM_MGMT);
        let capability_info = override_capability_info(capability_info);
        assert_eq!(capability_info.ess(), OVERRIDE_CAP_INFO_ESS);
        assert_eq!(capability_info.ibss(), OVERRIDE_CAP_INFO_IBSS);
        assert_eq!(capability_info.cf_pollable(), OVERRIDE_CAP_INFO_CF_POLLABLE);
        assert_eq!(capability_info.cf_poll_req(), OVERRIDE_CAP_INFO_CF_POLL_REQUEST);
        assert_eq!(capability_info.privacy(), OVERRIDE_CAP_INFO_PRIVACY);
        assert_eq!(capability_info.spectrum_mgmt(), OVERRIDE_CAP_INFO_SPECTRUM_MGMT);
    }

    #[test]
    fn test_override_ht_cap() {
        let mut ht_cap = ie::fake_ht_capabilities();
        let ht_cap_info = ht_cap
            .ht_cap_info
            .with_tx_stbc(!OVERRIDE_HT_CAP_INFO_TX_STBC)
            .with_chan_width_set(ie::ChanWidthSet::TWENTY_FORTY);
        ht_cap.ht_cap_info = ht_cap_info;
        let mut channel = Channel::new(153, Cbw::Cbw20, fidl_ieee80211::WlanBand::FiveGhz);

        let ht_cap_info = override_ht_capabilities(ht_cap, channel.cbw).ht_cap_info;
        assert_eq!(ht_cap_info.tx_stbc(), OVERRIDE_HT_CAP_INFO_TX_STBC);
        assert_eq!(ht_cap_info.chan_width_set(), ie::ChanWidthSet::TWENTY_ONLY);

        channel.cbw = Cbw::Cbw40;
        let ht_cap_info = override_ht_capabilities(ht_cap, channel.cbw).ht_cap_info;
        assert_eq!(ht_cap_info.chan_width_set(), ie::ChanWidthSet::TWENTY_FORTY);
    }

    #[test]
    fn test_override_vht_cap() {
        let mut vht_cap = ie::fake_vht_capabilities();
        let vht_cap_info = vht_cap.vht_cap_info.with_supported_cbw_set(2);
        vht_cap.vht_cap_info = vht_cap_info;
        let mut channel = Channel::new(153, Cbw::Cbw20, fidl_ieee80211::WlanBand::FiveGhz);

        // CBW20, CBW40, CBW80 will set supported_cbw_set to 0

        let vht_cap_info = override_vht_capabilities(vht_cap, channel.cbw).vht_cap_info;
        assert_eq!(vht_cap_info.supported_cbw_set(), OVERRIDE_VHT_CAP_INFO_SUPPORTED_CBW_SET);

        channel.cbw = Cbw::Cbw40;
        let vht_cap_info = override_vht_capabilities(vht_cap, channel.cbw).vht_cap_info;
        assert_eq!(vht_cap_info.supported_cbw_set(), OVERRIDE_VHT_CAP_INFO_SUPPORTED_CBW_SET);

        channel.cbw = Cbw::Cbw80;
        let vht_cap_info = override_vht_capabilities(vht_cap, channel.cbw).vht_cap_info;
        assert_eq!(vht_cap_info.supported_cbw_set(), OVERRIDE_VHT_CAP_INFO_SUPPORTED_CBW_SET);

        // CBW160 and CBW80P80 will preserve existing supported_cbw_set value

        channel.cbw = Cbw::Cbw160;
        let vht_cap_info = override_vht_capabilities(vht_cap, channel.cbw).vht_cap_info;
        assert_eq!(vht_cap_info.supported_cbw_set(), 2);

        channel.cbw = Cbw::Cbw80P80 { secondary80: 42 };
        let vht_cap_info = override_vht_capabilities(vht_cap, channel.cbw).vht_cap_info;
        assert_eq!(vht_cap_info.supported_cbw_set(), 2);
    }

    #[test]
    fn test_get_device_band_cap() {
        let device_info = fidl_mlme::DeviceInfo {
            sta_addr: [0; 6],
            factory_addr: [0; 6],
            role: fidl_common::WlanMacRole::Client,
            bands: vec![fake_5ghz_band_capability_ht(ie::ChanWidthSet::TWENTY_FORTY)],
            softmac_hardware_capability: 0,
            qos_capable: true,
        };
        assert_eq!(
            fidl_ieee80211::WlanBand::FiveGhz,
            get_band_cap_for_channel(
                &device_info.bands[..],
                Channel::new(36, Cbw::Cbw20, fidl_ieee80211::WlanBand::FiveGhz)
            )
            .unwrap()
            .band
        );
    }

    fn fake_client_join_cap() -> ClientCapabilities {
        ClientCapabilities(StaCapabilities {
            capability_info: mac::CapabilityInfo(0x1234),
            rates: [101, 102, 103, 104].iter().cloned().map(SupportedRate).collect(),
            ht_cap: Some(HtCapabilities {
                ht_cap_info: ie::HtCapabilityInfo(0).with_rx_stbc(2).with_tx_stbc(false),
                ..ie::fake_ht_capabilities()
            }),
            vht_cap: Some(ie::fake_vht_capabilities()),
        })
    }

    fn fake_ap_join_cap() -> ApCapabilities {
        ApCapabilities(StaCapabilities {
            capability_info: mac::CapabilityInfo(0x4321),
            // 101 + 128 turns it into a basic rate
            rates: [101 + 128, 102, 9].iter().cloned().map(SupportedRate).collect(),
            ht_cap: Some(HtCapabilities {
                ht_cap_info: ie::HtCapabilityInfo(0).with_rx_stbc(1).with_tx_stbc(true),
                ..ie::fake_ht_capabilities()
            }),
            vht_cap: Some(ie::fake_vht_capabilities()),
        })
    }

    #[test]
    fn client_intersect_with_ap() {
        let caps = assert_matches!(
            intersect_with_ap_as_client(&fake_client_join_cap(), &fake_ap_join_cap()),
            Ok(caps) => caps
        );
        assert_eq!(
            caps,
            StaCapabilities {
                capability_info: mac::CapabilityInfo(0x0220),
                rates: [229, 102].iter().cloned().map(SupportedRate).collect(),
                ht_cap: Some(HtCapabilities {
                    ht_cap_info: ie::HtCapabilityInfo(0).with_rx_stbc(2).with_tx_stbc(false),
                    ..ie::fake_ht_capabilities()
                }),
                ..fake_client_join_cap().0
            }
        )
    }

    #[test]
    fn ap_intersect_with_remote_client() {
        assert_eq!(
            intersect_with_remote_client_as_ap(&fake_ap_join_cap(), &fake_client_join_cap()),
            StaCapabilities {
                capability_info: mac::CapabilityInfo(0x0220),
                rates: [229, 102].iter().cloned().map(SupportedRate).collect(),
                ht_cap: Some(HtCapabilities {
                    ht_cap_info: ie::HtCapabilityInfo(0).with_rx_stbc(0).with_tx_stbc(true),
                    ..ie::fake_ht_capabilities()
                }),
                ..fake_ap_join_cap().0
            }
        );
    }
}