[PATCH v2] mac80211: Fix [re]association power saving issue on AP side

[PATCH v2] mac80211: Fix [re]association power saving issue on AP side

[Igor Perminov]

Consider the following step-by step:
1. A STA authenticates and associates with the AP and exchanges
traffic.
2. The STA reports to the AP that it is going to PS state.
3. Some time later the STA device goes to the stand-by mode (not only
its wi-fi card, but the device itself) and drops the association state
without sending a disassociation frame.
4. The STA device wakes up and begins authentication with an
Auth frame as it hasn't been authenticated/associated previously.
 
At the step 4 the AP "remembers" the STA and considers it is still in
the PS state, so the AP buffers frames, which it has to send to the STA.
But the STA isn't actually in the PS state and so it neither checks
TIM bits nor reports to the AP that it isn't power saving.
Because of that authentication/[re]association fails.

To fix authentication/[re]association stage of this issue, Auth, Assoc
Resp and Reassoc Resp frames are transmitted disregarding of STA's power
saving state.

N.B. This patch doesn't fix further data frame exchange after
authentication/[re]association. A patch in hostapd is required to fix
that.

Signed-off-by: Igor Perminov <igor.perminov@inbox.ru>
---
 net/mac80211/tx.c       |    5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)

diff --git a/net/mac80211/tx.c b/net/mac80211/tx.c
index 10a1099..4d981e7 100644
--- a/net/mac80211/tx.c
+++ b/net/mac80211/tx.c
@@ -367,7 +367,10 @@ ieee80211_tx_h_unicast_ps_buf(struct ieee80211_tx_data *tx)
 	struct ieee80211_hdr *hdr = (struct ieee80211_hdr *)tx->skb->data;
 	u32 staflags;
 
-	if (unlikely(!sta || ieee80211_is_probe_resp(hdr->frame_control)))
+	if (unlikely(!sta || ieee80211_is_probe_resp(hdr->frame_control)
+			|| ieee80211_is_auth(hdr->frame_control)
+			|| ieee80211_is_assoc_resp(hdr->frame_control)
+			|| ieee80211_is_reassoc_resp(hdr->frame_control)))
 		return TX_CONTINUE;
 
 	staflags = get_sta_flags(sta);

Re: [PATCH v2] mac80211: Fix [re]association power saving issue on AP side

[Johannes Berg]

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On Tue, 2009-09-22 at 00:25 +0400, Igor Perminov wrote:
> Consider the following step-by step:

NACK this, we'll take care of it properly with the required cleanup as
mentioned.

johannes

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Re: [PATCH v2] mac80211: Fix [re]association power saving issue on AP side

[Jouni Malinen]

On Tue, Sep 22, 2009 at 12:25:44AM +0400, Igor Perminov wrote:

> At the step 4 the AP "remembers" the STA and considers it is still in
> the PS state, so the AP buffers frames, which it has to send to the STA.
> But the STA isn't actually in the PS state and so it neither checks
> TIM bits nor reports to the AP that it isn't power saving.
> Because of that authentication/[re]association fails.
> 
> To fix authentication/[re]association stage of this issue, Auth, Assoc
> Resp and Reassoc Resp frames are transmitted disregarding of STA's power
> saving state.

That looks fine to me and should be applied.

> N.B. This patch doesn't fix further data frame exchange after
> authentication/[re]association. A patch in hostapd is required to fix
> that.

Git snapshot of hostapd is now removing the STA entry (if one exists)
when processing reassociation. The combination of these two changes
allows the reassociation back to the same AP to be completed even if the
STA was in PS mode.

-- 
Jouni Malinen                                            PGP id EFC895FA

Re: [PATCH v2] mac80211: Fix [re]association power saving issue on AP side

[Johannes Berg]

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On Sat, 2009-09-26 at 21:34 +0300, Jouni Malinen wrote:
> On Tue, Sep 22, 2009 at 12:25:44AM +0400, Igor Perminov wrote:
> 
> > At the step 4 the AP "remembers" the STA and considers it is still in
> > the PS state, so the AP buffers frames, which it has to send to the STA.
> > But the STA isn't actually in the PS state and so it neither checks
> > TIM bits nor reports to the AP that it isn't power saving.
> > Because of that authentication/[re]association fails.
> > 
> > To fix authentication/[re]association stage of this issue, Auth, Assoc
> > Resp and Reassoc Resp frames are transmitted disregarding of STA's power
> > saving state.
> 
> That looks fine to me and should be applied.

Alright, I'll take back my NACK then, just thought it'd be easier to do
the cleanup in the same patch but I can also do it separately.

johannes

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