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Subject[PATCH v2] mac80211: fix race in ieee80211_register_hw()
Date
A race condition leading to a kernel crash is observed during invocation
of ieee80211_register_hw() on a dragonboard410c device having wcn36xx
driver built as a loadable module along with a wifi manager in user-space
waiting for a wifi device (wlanX) to be active.

Sequence diagram for a particular kernel crash scenario:

user-space ieee80211_register_hw() ieee80211_tasklet_handler()
++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
| | |
|<---phy0----wiphy_register() |
|-----iwd if_add---->| |
| |<---IRQ----(RX packet)
| Kernel crash |
| due to unallocated |
| workqueue. |
| | |
| alloc_ordered_workqueue() |
| | |
| Misc wiphy init. |
| | |
| ieee80211_if_add() |
| | |

As evident from above sequence diagram, this race condition isn't specific
to a particular wifi driver but rather the initialization sequence in
ieee80211_register_hw() needs to be fixed. So re-order the initialization
sequence and the updated sequence diagram would look like:

user-space ieee80211_register_hw() ieee80211_tasklet_handler()
++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
| | |
| alloc_ordered_workqueue() |
| | |
| Misc wiphy init. |
| | |
|<---phy0----wiphy_register() |
|-----iwd if_add---->| |
| |<---IRQ----(RX packet)
| | |
| ieee80211_if_add() |
| | |

Cc: <stable@vger.kernel.org>
Signed-off-by: Sumit Garg <sumit.garg@linaro.org>
---

Changes in v2:
- Move rtnl_unlock() just after ieee80211_init_rate_ctrl_alg().
- Update sequence diagrams in commit message for more clarification.

net/mac80211/main.c | 22 +++++++++++++---------
1 file changed, 13 insertions(+), 9 deletions(-)

diff --git a/net/mac80211/main.c b/net/mac80211/main.c
index 4c2b5ba..d497129 100644
--- a/net/mac80211/main.c
+++ b/net/mac80211/main.c
@@ -1051,7 +1051,7 @@ int ieee80211_register_hw(struct ieee80211_hw *hw)
local->hw.wiphy->signal_type = CFG80211_SIGNAL_TYPE_UNSPEC;
if (hw->max_signal <= 0) {
result = -EINVAL;
- goto fail_wiphy_register;
+ goto fail_workqueue;
}
}

@@ -1113,7 +1113,7 @@ int ieee80211_register_hw(struct ieee80211_hw *hw)

result = ieee80211_init_cipher_suites(local);
if (result < 0)
- goto fail_wiphy_register;
+ goto fail_workqueue;

if (!local->ops->remain_on_channel)
local->hw.wiphy->max_remain_on_channel_duration = 5000;
@@ -1139,10 +1139,6 @@ int ieee80211_register_hw(struct ieee80211_hw *hw)

local->hw.wiphy->max_num_csa_counters = IEEE80211_MAX_CSA_COUNTERS_NUM;

- result = wiphy_register(local->hw.wiphy);
- if (result < 0)
- goto fail_wiphy_register;
-
/*
* We use the number of queues for feature tests (QoS, HT) internally
* so restrict them appropriately.
@@ -1207,6 +1203,8 @@ int ieee80211_register_hw(struct ieee80211_hw *hw)
goto fail_rate;
}

+ rtnl_unlock();
+
if (local->rate_ctrl) {
clear_bit(IEEE80211_HW_SUPPORTS_VHT_EXT_NSS_BW, hw->flags);
if (local->rate_ctrl->ops->capa & RATE_CTRL_CAPA_VHT_EXT_NSS_BW)
@@ -1254,6 +1252,12 @@ int ieee80211_register_hw(struct ieee80211_hw *hw)
local->sband_allocated |= BIT(band);
}

+ result = wiphy_register(local->hw.wiphy);
+ if (result < 0)
+ goto fail_wiphy_register;
+
+ rtnl_lock();
+
/* add one default STA interface if supported */
if (local->hw.wiphy->interface_modes & BIT(NL80211_IFTYPE_STATION) &&
!ieee80211_hw_check(hw, NO_AUTO_VIF)) {
@@ -1293,6 +1297,8 @@ int ieee80211_register_hw(struct ieee80211_hw *hw)
#if defined(CONFIG_INET) || defined(CONFIG_IPV6)
fail_ifa:
#endif
+ wiphy_unregister(local->hw.wiphy);
+ fail_wiphy_register:
rtnl_lock();
rate_control_deinitialize(local);
ieee80211_remove_interfaces(local);
@@ -1302,8 +1308,6 @@ int ieee80211_register_hw(struct ieee80211_hw *hw)
ieee80211_led_exit(local);
destroy_workqueue(local->workqueue);
fail_workqueue:
- wiphy_unregister(local->hw.wiphy);
- fail_wiphy_register:
if (local->wiphy_ciphers_allocated)
kfree(local->hw.wiphy->cipher_suites);
kfree(local->int_scan_req);
@@ -1353,8 +1357,8 @@ void ieee80211_unregister_hw(struct ieee80211_hw *hw)
skb_queue_purge(&local->skb_queue_unreliable);
skb_queue_purge(&local->skb_queue_tdls_chsw);

- destroy_workqueue(local->workqueue);
wiphy_unregister(local->hw.wiphy);
+ destroy_workqueue(local->workqueue);
ieee80211_led_exit(local);
kfree(local->int_scan_req);
}
--
2.7.4
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