Subject: Re: [PATCH] nl80211: take RCU read lock when calling ieee80211_bss_get_ie()

From: Johannes Berg <[email-masked]>
Date: Sun, 14 Jan 2018 22:58:22 +0100

Hi,

> Fixes: 44905265bc15 ("nl80211: don't expose wdev->ssid for most interfaces")
> Signed-off-by: Dominik Brodowski <[email-masked]>
> ---
> 
> This patch fixes the regression I reported in the last couple of weeks for
> various v4.15-rcX revisions to netdev, where a "suspicious RCU usage"
> showed up in net/wireless/util.c:778.

Huh. You should added linux-wireless to those reports, I simply didn't
see them!

> diff --git a/net/wireless/nl80211.c b/net/wireless/nl80211.c
> index 2b3dbcd40e46..1eecc249fb5e 100644
> --- a/net/wireless/nl80211.c
> +++ b/net/wireless/nl80211.c
> @@ -2618,8 +2618,10 @@ static int nl80211_send_iface(struct sk_buff *msg, u32 portid, u32 seq, int flag
>  		const u8 *ssid_ie;
>  		if (!wdev->current_bss)
>  			break;
> +		rcu_read_lock();
>  		ssid_ie = ieee80211_bss_get_ie(&wdev->current_bss->pub,
>  					       WLAN_EID_SSID);
> +		rcu_read_unlock();
>  		if (!ssid_ie)
>  			break;
>  		if (nla_put(msg, NL80211_ATTR_SSID, ssid_ie[1], ssid_ie + 2))

This uses the ssid_ie, so that doesn't really seem right? The
protection should extend beyond the usage.

johannes