Suspicious RCU from iwlwifi driver

Suspicious RCU from iwlwifi driver

[Laura Abbott]

Hi,

I'm currently seeing a suspicous RCU usage warning:

===============================
[ INFO: suspicious RCU usage. ]
  4.4.0-rc4-next-20151210 #23 Not tainted
  -------------------------------
  drivers/net/wireless/intel/iwlwifi/mvm/sta.c:1226 suspicious rcu_dereference_protected() usage!
  
  other info that might help us debug this:
  
  rcu_scheduler_active = 1, debug_locks = 0
  4 locks held by irq/34-iwlwifi/978:
   #0:  (sync_cmd_lockdep_map){++++..}, at: [<ffffffffa073c1f5>] iwl_pcie_irq_handler+0x5/0x1870 [iwlwifi]
   #1:  (&(&rxq->lock)->rlock){+.+...}, at: [<ffffffffa073cafa>] iwl_pcie_irq_handler+0x90a/0x1870 [iwlwifi]
   #2:  (rcu_read_lock){......}, at: [<ffffffffa0827793>] ieee80211_rx_napi+0xc3/0xbd0 [mac80211]
   #3:  (&(&local->rx_path_lock)->rlock){+.....}, at: [<ffffffffa0823fce>] ieee80211_rx_handlers+0x3e/0x2c80 [mac80211]
  
   stack backtrace:
  CPU: 4 PID: 978 Comm: irq/34-iwlwifi Not tainted 4.4.0-rc4-next-20151210 #23
  Hardware name: LENOVO 20BFS0EC00/20BFS0EC00, BIOS GMET62WW (2.10 ) 03/19/2014
   0000000000000000 000000005a05ae61 ffff880407dc3760 ffffffff81434b69
   ffff8804053e3200 ffff880407dc3790 ffffffff81106757 0000000000000000
   ffff880408d8a868 ffff880408d8a868 ffff8804061cc630 ffff880407dc37b0
  Call Trace:
   [<ffffffff81434b69>] dump_stack+0x4b/0x72
   [<ffffffff81106757>] lockdep_rcu_suspicious+0xd7/0x110
   [<ffffffffa090eff8>] iwl_mvm_get_key_sta_id.part.3+0x88/0x90 [iwlmvm]
   [<ffffffffa09116b1>] iwl_mvm_update_tkip_key+0x241/0x280 [iwlmvm]
   [<ffffffffa08fde6c>] iwl_mvm_mac_update_tkip_key+0x1c/0x20 [iwlmvm]
   [<ffffffffa0816e89>] ieee80211_tkip_decrypt_data+0x249/0x5f0 [mac80211]
   [<ffffffff81729177>] ? skb_copy_bits+0x137/0x2f0
   [<ffffffff8172ba55>] ? __pskb_pull_tail+0x85/0x3a0
   [<ffffffffa080010e>] ieee80211_crypto_tkip_decrypt+0xce/0x150 [mac80211]
   [<ffffffffa0824900>] ieee80211_rx_handlers+0x970/0x2c80 [mac80211]
   [<ffffffff8110923a>] ? __lock_acquire+0x4ba/0x1b70
   [<ffffffffa0826df4>] ieee80211_prepare_and_rx_handle+0x1e4/0xac0 [mac80211]
   [<ffffffffa0827a06>] ieee80211_rx_napi+0x336/0xbd0 [mac80211]
   [<ffffffffa0827793>] ? ieee80211_rx_napi+0xc3/0xbd0 [mac80211]
   [<ffffffffa090adcd>] iwl_mvm_rx_rx_mpdu+0x4ad/0x880 [iwlmvm]
   [<ffffffffa090ab02>] ? iwl_mvm_rx_rx_mpdu+0x1e2/0x880 [iwlmvm]
   [<ffffffffa0905076>] iwl_mvm_rx+0x56/0x240 [iwlmvm]
   [<ffffffffa073d17c>] iwl_pcie_irq_handler+0xf8c/0x1870 [iwlwifi]
   [<ffffffff81882934>] ? __schedule+0x414/0xaf0
   [<ffffffff81120310>] irq_thread_fn+0x20/0x50
   [<ffffffff8112058b>] irq_thread+0x16b/0x1f0
   [<ffffffff81882934>] ? __schedule+0x414/0xaf0
   [<ffffffff811202f0>] ? irq_forced_thread_fn+0x70/0x70
   [<ffffffff81120370>] ? wake_threads_waitq+0x30/0x30
   [<ffffffff81120420>] ? irq_thread_dtor+0xb0/0xb0
   [<ffffffff810d3091>] kthread+0x101/0x120
   [<ffffffff81108999>] ? trace_hardirqs_on_caller+0x129/0x1b0
   [<ffffffff810d2f90>] ? kthread_create_on_node+0x250/0x250
   [<ffffffff81889e1f>] ret_from_fork+0x3f/0x70
   [<ffffffff810d2f90>] ? kthread_create_on_node+0x250/0x250

If I revert 9513c5e18a0dc55a1fc9c890715098ba2315830b
(iwlwifi: mvm: Avoid dereferencing sta if it was already flushed)
The warning goes away. Known issue?

Thanks,
Laura

Re: Suspicious RCU from iwlwifi driver

[Johannes Berg]

Hi Laura,

>   drivers/net/wireless/intel/iwlwifi/mvm/sta.c:1226 suspicious
> rcu_dereference_protected() usage!

> If I revert 9513c5e18a0dc55a1fc9c890715098ba2315830b
> (iwlwifi: mvm: Avoid dereferencing sta if it was already flushed)
> The warning goes away. Known issue?

Thanks for the report - I at least hadn't seen this (or a fix for it)
yet, we'll take a look.

johannes

[PATCH] iwlwifi: mvm: protect RCU dereference in iwl_mvm_get_key_sta_id

[Johannes Berg]

From: Johannes Berg <johannes.berg@intel.com>

Properly protect the RCU dereference in iwl_mvm_get_key_sta_id() when
coming from iwl_mvm_update_tkip_key() which cannot hold the mvm->mutex
by moving the call into the RCU critical section.
Modify the check to use rcu_dereference_check() to permit this.

Fixes: 9513c5e18a0d ("iwlwifi: mvm: Avoid dereferencing sta if it was already flushed")
Reported-by: Laura Abbott <labbott@redhat.com>
Signed-off-by: Johannes Berg <johannes.berg@intel.com>
---
 drivers/net/wireless/iwlwifi/mvm/sta.c | 15 +++++++++------
 1 file changed, 9 insertions(+), 6 deletions(-)

diff --git a/drivers/net/wireless/iwlwifi/mvm/sta.c b/drivers/net/wireless/iwlwifi/mvm/sta.c
index 354acbde088e..2b976b110207 100644
--- a/drivers/net/wireless/iwlwifi/mvm/sta.c
+++ b/drivers/net/wireless/iwlwifi/mvm/sta.c
@@ -1222,8 +1222,8 @@ static u8 iwl_mvm_get_key_sta_id(struct iwl_mvm *mvm,
 	    mvmvif->ap_sta_id != IWL_MVM_STATION_COUNT) {
 		u8 sta_id = mvmvif->ap_sta_id;
 
-		sta = rcu_dereference_protected(mvm->fw_id_to_mac_id[sta_id],
-						lockdep_is_held(&mvm->mutex));
+		sta = rcu_dereference_check(mvm->fw_id_to_mac_id[sta_id],
+					    lockdep_is_held(&mvm->mutex));
 		/*
 		 * It is possible that the 'sta' parameter is NULL,
 		 * for example when a GTK is removed - the sta_id will then
@@ -1590,14 +1590,15 @@ void iwl_mvm_update_tkip_key(struct iwl_mvm *mvm,
 			     u16 *phase1key)
 {
 	struct iwl_mvm_sta *mvm_sta;
-	u8 sta_id = iwl_mvm_get_key_sta_id(mvm, vif, sta);
+	u8 sta_id;
 	bool mcast = !(keyconf->flags & IEEE80211_KEY_FLAG_PAIRWISE);
 
-	if (WARN_ON_ONCE(sta_id == IWL_MVM_STATION_COUNT))
-		return;
-
 	rcu_read_lock();
 
+	sta_id = iwl_mvm_get_key_sta_id(mvm, vif, sta);
+	if (WARN_ON_ONCE(sta_id == IWL_MVM_STATION_COUNT))
+		goto unlock;
+
 	if (!sta) {
 		sta = rcu_dereference(mvm->fw_id_to_mac_id[sta_id]);
 		if (WARN_ON(IS_ERR_OR_NULL(sta))) {
@@ -1609,6 +1610,8 @@ void iwl_mvm_update_tkip_key(struct iwl_mvm *mvm,
 	mvm_sta = iwl_mvm_sta_from_mac80211(sta);
 	iwl_mvm_send_sta_key(mvm, mvm_sta, keyconf, mcast,
 			     iv32, phase1key, CMD_ASYNC, keyconf->hw_key_idx);
+
+ unlock:
 	rcu_read_unlock();
 }
 
-- 
2.6.2

Re: [PATCH] iwlwifi: mvm: protect RCU dereference in iwl_mvm_get_key_sta_id

[Laura Abbott]

On 12/11/2015 12:13 AM, Johannes Berg wrote:
> From: Johannes Berg <johannes.berg@intel.com>
>
> Properly protect the RCU dereference in iwl_mvm_get_key_sta_id() when
> coming from iwl_mvm_update_tkip_key() which cannot hold the mvm->mutex
> by moving the call into the RCU critical section.
> Modify the check to use rcu_dereference_check() to permit this.
>
> Fixes: 9513c5e18a0d ("iwlwifi: mvm: Avoid dereferencing sta if it was already flushed")
> Reported-by: Laura Abbott <labbott@redhat.com>
> Signed-off-by: Johannes Berg <johannes.berg@intel.com>

Thanks, it's working for me.

Tested-by: Laura Abbott <labbott@redhat.com>