To:     linux-wireless@vger.kernel.org
From:   Denis Kenzior <denkenz@gmail.com>
Subject: NL80211_SCAN_FLAG_RANDOM_ADDR ?
Message-ID: <e09a9bc7-9774-334b-53e8-13e1d781bee3@gmail.com>
Date:   Thu, 11 Apr 2019 17:30:55 -0500
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Hi,

I've been poking around at how this flag is used and I noticed this 
check in net/wireless/nl80211.c:

nl80211_check_scan_flags()

         if (*flags & NL80211_SCAN_FLAG_RANDOM_ADDR) {
                 int err;

                 if (!(wiphy->features & randomness_flag) ||
                     (wdev && wdev->current_bss))
                         return -EOPNOTSUPP;


The above disallows the use of RANDOM_ADDR for scans while connected. 
The nl80211.h uapi header seems to concur:

  "@NL80211_FEATURE_SCAN_RANDOM_MAC_ADDR: This device/driver supports 
using a random MAC address during scan (if the device is unassociated);"

However, if I create a P2P Device (in addition to the default STA 
device), the kernel happily lets me scan on the wdev while the STA 
interface is connected.

sudo iw phy0 interface add p2p type __p2pdev
sudo iw wdev 0x2 p2p start
sudo iw wdev 0x2 scan randomize

So the immediate question I have is, should the RANDOM_ADDR flag indeed 
be limited to unassociated STA interfaces?  It would seem the hardware 
is capable randomizing even when connected? Please educate me :)

Regards,
-Denis