Re: [PATCH] mac80211: do not TX injected frames when not allowed

[Johannes Berg <johannes@sipsolutions.net>]

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On Mon, 2009-01-26 at 16:22 -0800, Luis R. Rodriguez wrote:
> Monitor mode is able to TX by using injected frames. We should
> not allow injected frames to be sent unless allowed by regulatory
> rules. Since AP mode uses a monitor interfaces to transmit
> management frames we have to take care to not break AP mode as
> well while resolving this. We deal with this by allowing compliant
> APs solutions to inform mac80211 if their monitor interface is
> intended to be used for an AP by setting a cfg80211 flag for the
> monitor interface. hostapd, for example, currently does its own
> checks to ensure AP mode is not used on channels which require radar
> detection. Once such solutions are available it can can enable this
> flag.
> 
> Signed-off-by: Luis R. Rodriguez <lrodriguez@atheros.com>
> ---
> 
> This now works, I moved the check as recommended by Johannes to
> ieee80211_monitor_start_xmit(), the issues I ran into earlier seem
> to be due to a work around set in place for 11w.
> 
>  include/linux/nl80211.h |    3 +++
>  include/net/cfg80211.h  |    4 ++++
>  net/mac80211/tx.c       |   14 ++++++++++++++
>  net/wireless/nl80211.c  |    1 +
>  4 files changed, 22 insertions(+), 0 deletions(-)
> 
> diff --git a/include/linux/nl80211.h b/include/linux/nl80211.h
> index 76aae3d..3357907 100644
> --- a/include/linux/nl80211.h
> +++ b/include/linux/nl80211.h
> @@ -705,6 +705,8 @@ enum nl80211_reg_rule_flags {
>   * @NL80211_MNTR_FLAG_OTHER_BSS: disable BSSID filtering
>   * @NL80211_MNTR_FLAG_COOK_FRAMES: report frames after processing.
>   *	overrides all other flags.
> + * @NL80211_MNTR_FLAG_AP_MGT: this monitor interface is used for AP mode
> + * 	to be able to inject management frames.
>   *
>   * @__NL80211_MNTR_FLAG_AFTER_LAST: internal use
>   * @NL80211_MNTR_FLAG_MAX: highest possible monitor flag
> @@ -716,6 +718,7 @@ enum nl80211_mntr_flags {
>  	NL80211_MNTR_FLAG_CONTROL,
>  	NL80211_MNTR_FLAG_OTHER_BSS,
>  	NL80211_MNTR_FLAG_COOK_FRAMES,
> +	NL80211_MNTR_FLAG_AP_MGT,
>  
>  	/* keep last */
>  	__NL80211_MNTR_FLAG_AFTER_LAST,
> diff --git a/include/net/cfg80211.h b/include/net/cfg80211.h
> index dd1fd51..fe65c64 100644
> --- a/include/net/cfg80211.h
> +++ b/include/net/cfg80211.h
> @@ -255,6 +255,9 @@ struct station_info {
>   * @MONITOR_FLAG_CONTROL: pass control frames
>   * @MONITOR_FLAG_OTHER_BSS: disable BSSID filtering
>   * @MONITOR_FLAG_COOK_FRAMES: report frames after processing
> + * @MONITOR_FLAG_AP_MGT: informs us this monitor interface is
> + *	used by a driver for AP mode to be able to inject management
> + * 	frames.
>   */
>  enum monitor_flags {
>  	MONITOR_FLAG_FCSFAIL		= 1<<NL80211_MNTR_FLAG_FCSFAIL,
> @@ -262,6 +265,7 @@ enum monitor_flags {
>  	MONITOR_FLAG_CONTROL		= 1<<NL80211_MNTR_FLAG_CONTROL,
>  	MONITOR_FLAG_OTHER_BSS		= 1<<NL80211_MNTR_FLAG_OTHER_BSS,
>  	MONITOR_FLAG_COOK_FRAMES	= 1<<NL80211_MNTR_FLAG_COOK_FRAMES,
> +	MONITOR_FLAG_AP_MGT		= 1<<NL80211_MNTR_FLAG_AP_MGT,
>  };
>  
>  /**
> diff --git a/net/mac80211/tx.c b/net/mac80211/tx.c
> index 7b013fb..e752f6d 100644
> --- a/net/mac80211/tx.c
> +++ b/net/mac80211/tx.c
> @@ -1432,11 +1432,25 @@ int ieee80211_master_start_xmit(struct sk_buff *skb, struct net_device *dev)
>  int ieee80211_monitor_start_xmit(struct sk_buff *skb,
>  				 struct net_device *dev)
>  {
> +	struct ieee80211_sub_if_data *sdata = IEEE80211_DEV_TO_SUB_IF(dev);
>  	struct ieee80211_local *local = wdev_priv(dev->ieee80211_ptr);
> +	struct ieee80211_channel *chan = local->hw.conf.channel;
>  	struct ieee80211_radiotap_header *prthdr =
>  		(struct ieee80211_radiotap_header *)skb->data;
>  	u16 len_rthdr;
>  
> +	/* Frame injection is not allowed if beaconing is not allowed

Comment style, /* on a single line please :)

> +	 * or if we need radar detection. Beaconing is usually not allowed when
> +	 * the mode or operation (Adhoc, AP, Mesh) does not support DFS.
> +	 * Since AP mode uses monitor interfaces to inject/TX management
> +	 * frames we make AP mode the exception to this rule as its
> +	 * implementation can deal with radar detection by itself. */

and end with */ on its own line.

> +	if (WARN_ON(sdata->vif.type != NL80211_IFTYPE_MONITOR))
> +		return TX_DROP;

Huh? You're in monitor_start_xmit. If that goes wrong, something is
horribly broken and beyond WARN_ON. Please just remove this.

Other than that, looks good.

johannes

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