mac80211: fix RCU usage in ieee80211_tx_h_select_key()

ieee80211_tx_h_select_key() is performing a series of RCU dereferences,
but none of the callers seems to be taking RCU read-side lock; let's
acquire the lock in ieee80211_tx_h_select_key() itself.

Spotted with rtw89 driver.

This fixes the splat below.

 =============================
 WARNING: suspicious RCU usage
 5.17.0-rc4-00003-gccad664b7f14 #3 Tainted: G            E
 -----------------------------
 net/mac80211/tx.c:593 suspicious rcu_dereference_check() usage!

 other info that might help us debug this:

 rcu_scheduler_active = 2, debug_locks = 1
 2 locks held by kworker/u33:0/184:
  #0: ffff9c0b14811d38 ((wq_completion)rtw89_tx_wq){+.+.}-{0:0}, at: process_one_work+0x258/0x660
  #1: ffffb97380cf3e78 ((work_completion)(&rtwdev->txq_work)){+.+.}-{0:0}, at: process_one_work+0x258/0x660

 stack backtrace:
 CPU: 8 PID: 184 Comm: kworker/u33:0 Tainted: G            E     5.17.0-rc4-00003-gccad664b7f14 #3 473b49ab0e7c2d6af2900c756bfd04efd7a9de13
 Hardware name: LENOVO 20UJS2B905/20UJS2B905, BIOS R1CET63W(1.32 ) 04/09/2021
 Workqueue: rtw89_tx_wq rtw89_core_txq_work [rtw89_core]
 Call Trace:
  <TASK>
  dump_stack_lvl+0x58/0x71
  ieee80211_tx_h_select_key+0x2c0/0x530 [mac80211 911c23e2351c0ae60b597a67b1204a5ea955e365]
  ieee80211_tx_dequeue+0x1a7/0x1260 [mac80211 911c23e2351c0ae60b597a67b1204a5ea955e365]
  rtw89_core_txq_work+0x1a6/0x420 [rtw89_core b39ba493f2e517ad75e0f8187ecc24edf58bbbea]
  process_one_work+0x2d8/0x660
  worker_thread+0x39/0x3e0
  ? process_one_work+0x660/0x660
  kthread+0xe5/0x110
  ? kthread_complete_and_exit+0x20/0x20
  ret_from_fork+0x22/0x30
  </TASK>

 =============================
 WARNING: suspicious RCU usage
 5.17.0-rc4-00003-gccad664b7f14 #3 Tainted: G            E
 -----------------------------
 net/mac80211/tx.c:607 suspicious rcu_dereference_check() usage!

 other info that might help us debug this:

 rcu_scheduler_active = 2, debug_locks = 1
 2 locks held by kworker/u33:0/184:
  #0: ffff9c0b14811d38 ((wq_completion)rtw89_tx_wq){+.+.}-{0:0}, at: process_one_work+0x258/0x660
  #1: ffffb97380cf3e78 ((work_completion)(&rtwdev->txq_work)){+.+.}-{0:0}, at: process_one_work+0x258/0x660

 stack backtrace:
 CPU: 8 PID: 184 Comm: kworker/u33:0 Tainted: G            E     5.17.0-rc4-00003-gccad664b7f14 #3 473b49ab0e7c2d6af2900c756bfd04efd7a9de13
 Hardware name: LENOVO 20UJS2B905/20UJS2B905, BIOS R1CET63W(1.32 ) 04/09/2021
 Workqueue: rtw89_tx_wq rtw89_core_txq_work [rtw89_core]
 Call Trace:
  <TASK>
  dump_stack_lvl+0x58/0x71
  ieee80211_tx_h_select_key+0x464/0x530 [mac80211 911c23e2351c0ae60b597a67b1204a5ea955e365]
  ieee80211_tx_dequeue+0x1a7/0x1260 [mac80211 911c23e2351c0ae60b597a67b1204a5ea955e365]
  rtw89_core_txq_work+0x1a6/0x420 [rtw89_core b39ba493f2e517ad75e0f8187ecc24edf58bbbea]
  process_one_work+0x2d8/0x660
  worker_thread+0x39/0x3e0
  ? process_one_work+0x660/0x660
  kthread+0xe5/0x110
  ? kthread_complete_and_exit+0x20/0x20
  ret_from_fork+0x22/0x30
  </TASK>

Fixes: a0761a3 ("mac80211: drop data frames without key on encrypted links")
Fixes: 46f6b06 ("mac80211: Encrypt "Group addressed privacy" action frames")
Fixes: 3cfcf6a ("mac80211: 802.11w - Use BIP (AES-128-CMAC)")
Fixes: f7e0104 ("mac80211: support separate default keys")
Signed-off-by: Jiri Kosina <jkosina@suse.cz>

net/mac80211/tx.c

@@ -580,6 +580,7 @@ ieee80211_tx_h_check_control_port_protocol(struct ieee80211_tx_data *tx)
 static ieee80211_tx_result debug_noinline
 ieee80211_tx_h_select_key(struct ieee80211_tx_data *tx)
 {
+	int ret;
 	struct ieee80211_key *key;
 	struct ieee80211_tx_info *info = IEEE80211_SKB_CB(tx->skb);
 	struct ieee80211_hdr *hdr = (struct ieee80211_hdr *)tx->skb->data;
@@ -589,6 +590,8 @@ ieee80211_tx_h_select_key(struct ieee80211_tx_data *tx)
 		return TX_CONTINUE;
 	}
 
+	rcu_read_lock();
+
 	if (tx->sta &&
 	    (key = rcu_dereference(tx->sta->ptk[tx->sta->ptk_idx])))
 		tx->key = key;
@@ -645,18 +648,23 @@ ieee80211_tx_h_select_key(struct ieee80211_tx_data *tx)
 		}
 
 		if (unlikely(tx->key && tx->key->flags & KEY_FLAG_TAINTED &&
-			     !ieee80211_is_deauth(hdr->frame_control)))
-			return TX_DROP;
+			     !ieee80211_is_deauth(hdr->frame_control))) {
+			ret = TX_DROP;
+			goto out;
+		}
 
 		if (!skip_hw && tx->key &&
 		    tx->key->flags & KEY_FLAG_UPLOADED_TO_HARDWARE)
 			info->control.hw_key = &tx->key->conf;
 	} else if (ieee80211_is_data_present(hdr->frame_control) && tx->sta &&
 		   test_sta_flag(tx->sta, WLAN_STA_USES_ENCRYPTION)) {
-		return TX_DROP;
+		ret = TX_DROP;
+		goto out;
 	}
-
-	return TX_CONTINUE;
+	ret = TX_CONTINUE;
+out:
+	rcu_read_unlock();
+	return ret;
 }
 
 static ieee80211_tx_result debug_noinline