Re: NL80211_SCAN_FLAG_RANDOM_ADDR ?

[Ben Greear <greearb@candelatech.com>]

On 4/11/19 3:30 PM, Denis Kenzior wrote:
> 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 :)

You can be sure that each driver/hardware has its own bugs and limitations related to this.

Ath10k wave 1 and wave 2 that I am aware of would ignore and/or not ACK probe responses
sent back to an MAC address that is not that of the station itself.  And changing the mac of a station
would require complete re-association AFAIK.  That is likely just one of the many issues.

Thanks,
Ben


-- 
Ben Greear <greearb@candelatech.com>
Candela Technologies Inc  http://www.candelatech.com