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wifi: mac80211: fix BA session teardown race

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As previously reported by Alexander, whose commit 69403bad97
("wifi: mac80211: sdata can be NULL during AMPDU start") I'm
reverting as part of this commit, there's a race between station
destruction and aggregation setup, where the aggregation setup
can happen while the station is being removed and queue the work
after ieee80211_sta_tear_down_BA_sessions() has already run in
__sta_info_destroy_part1(), and thus the worker will run with a
now freed station. In his case, this manifested in a NULL sdata
pointer, but really there's no guarantee whatsoever.

The real issue seems to be that it's possible at all to have a
situation where this occurs - we want to stop the BA sessions
when doing _part1, but we cannot be sure, and WLAN_STA_BLOCK_BA
isn't necessarily effective since we don't know that the setup
isn't concurrently running and already got past the check.

Simply call ieee80211_sta_tear_down_BA_sessions() again in the
second part of station destruction, since at that point really
nothing else can hold a reference to the station any more.

Also revert the sdata checks since those are just misleading at
this point.

Signed-off-by: Johannes Berg <johannes.berg@intel.com>
This commit is contained in:
Johannes Berg 2023-08-29 20:16:11 +02:00
parent cbaccdc424
commit 05f136220d
3 changed files with 15 additions and 8 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

6
net/mac80211/agg-tx.c
View File

@ -497,7 +497,7 @@ void ieee80211_tx_ba_session_handle_start(struct sta_info *sta, int tid)
{
struct tid_ampdu_tx *tid_tx;
struct ieee80211_local *local = sta->local;
struct ieee80211_sub_if_data *sdata;
struct ieee80211_sub_if_data *sdata = sta->sdata;
struct ieee80211_ampdu_params params = {
.sta = &sta->sta,
.action = IEEE80211_AMPDU_TX_START,
@ -525,7 +525,6 @@ void ieee80211_tx_ba_session_handle_start(struct sta_info *sta, int tid)
*/
synchronize_net();
sdata = sta->sdata;
params.ssn = sta->tid_seq[tid] >> 4;
ret = drv_ampdu_action(local, sdata, &params);
tid_tx->ssn = params.ssn;
@ -539,9 +538,6 @@ void ieee80211_tx_ba_session_handle_start(struct sta_info *sta, int tid)
*/
set_bit(HT_AGG_STATE_DRV_READY, &tid_tx->state);
} else if (ret) {
if (!sdata)
return;
ht_dbg(sdata,
"BA request denied - HW unavailable for %pM tid %d\n",
sta->sta.addr, tid);

3
net/mac80211/driver-ops.c
View File

@ -409,9 +409,6 @@ int drv_ampdu_action(struct ieee80211_local *local,
might_sleep();
lockdep_assert_wiphy(local->hw.wiphy);
if (!sdata)
return -EIO;
sdata = get_bss_sdata(sdata);
if (!check_sdata_in_driver(sdata))
return -EIO;

14
net/mac80211/sta_info.c
View File

@ -1385,6 +1385,20 @@ static void __sta_info_destroy_part2(struct sta_info *sta, bool recalc)
* after _part1 and before _part2!
*/
/*
* There's a potential race in _part1 where we set WLAN_STA_BLOCK_BA
* but someone might have just gotten past a check, and not yet into
* queuing the work/creating the data/etc.
*
* Do another round of destruction so that the worker is certainly
* canceled before we later free the station.
*
* Since this is after synchronize_rcu()/synchronize_net() we're now
* certain that nobody can actually hold a reference to the STA and
* be calling e.g. ieee80211_start_tx_ba_session().
*/
ieee80211_sta_tear_down_BA_sessions(sta, AGG_STOP_DESTROY_STA);
might_sleep();
lockdep_assert_wiphy(local->hw.wiphy);