mac80211: Fix [re]association power saving issue on AP side
PATCH v2 1/1 mac80211: Fix [re]association power saving issue on AP side
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.
--- net/mac80211/tx.c | 5 ++++- 1 file changed, 4 insertions(+), 1 deletion(-)
net/mac80211/tx.c +4 -1
@@ -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);
Johannes Berg
maintainerQuoted 1 line · Igor Perminov
Consider the following step-by step:
NACK this, we'll take care of it properly with the required cleanup as mentioned.
johannes
Quoted 9 lines · Igor Perminov
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.
Quoted 3 lines
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.
Signature · 1 line
Jouni Malinen PGP id EFC895FA
Johannes Berg
maintainerQuoted 8 lines · Jouni Malinen
Quoted 6 lines · Igor Perminov
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.
Quoted 5 lines
Quoted 3 lines
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