[PATCH 4.4 045/143] cw1200: Fix concurrency use-after-free bugs in cw1200_hw_scan()

[Greg Kroah-Hartman]

4.4-stable review patch.  If anyone has any objections, please let me know.

------------------

[ Upstream commit 4f68ef64cd7feb1220232bd8f501d8aad340a099 ]

The function cw1200_bss_info_changed() and cw1200_hw_scan() can be
concurrently executed.
The two functions both access a possible shared variable "frame.skb".

This shared variable is freed by dev_kfree_skb() in cw1200_upload_beacon(),
which is called by cw1200_bss_info_changed(). The free operation is
protected by a mutex lock "priv->conf_mutex" in cw1200_bss_info_changed().

In cw1200_hw_scan(), this shared variable is accessed without the
protection of the mutex lock "priv->conf_mutex".
Thus, concurrency use-after-free bugs may occur.

To fix these bugs, the original calls to mutex_lock(&priv->conf_mutex) and
mutex_unlock(&priv->conf_mutex) are moved to the places, which can
protect the accesses to the shared variable.

Signed-off-by: Jia-Ju Bai <baijiaju1...@gmail.com>
Signed-off-by: Kalle Valo <kv...@codeaurora.org>
Signed-off-by: Sasha Levin <sas...@kernel.org>
---
 drivers/net/wireless/cw1200/scan.c | 13 ++++++-------
 1 file changed, 6 insertions(+), 7 deletions(-)

diff --git a/drivers/net/wireless/cw1200/scan.c 
b/drivers/net/wireless/cw1200/scan.c
index bff81b8d4164..9f1037e7e55c 100644
--- a/drivers/net/wireless/cw1200/scan.c
+++ b/drivers/net/wireless/cw1200/scan.c
@@ -78,6 +78,10 @@ int cw1200_hw_scan(struct ieee80211_hw *hw,
        if (req->n_ssids > WSM_SCAN_MAX_NUM_OF_SSIDS)
                return -EINVAL;
 
+       /* will be unlocked in cw1200_scan_work() */
+       down(&priv->scan.lock);
+       mutex_lock(&priv->conf_mutex);
+
        frame.skb = ieee80211_probereq_get(hw, priv->vif->addr, NULL, 0,
                req->ie_len);
        if (!frame.skb)
@@ -86,19 +90,15 @@ int cw1200_hw_scan(struct ieee80211_hw *hw,
        if (req->ie_len)
                memcpy(skb_put(frame.skb, req->ie_len), req->ie, req->ie_len);
 
-       /* will be unlocked in cw1200_scan_work() */
-       down(&priv->scan.lock);
-       mutex_lock(&priv->conf_mutex);
-
        ret = wsm_set_template_frame(priv, &frame);
        if (!ret) {
                /* Host want to be the probe responder. */
                ret = wsm_set_probe_responder(priv, true);
        }
        if (ret) {
+               dev_kfree_skb(frame.skb);
                mutex_unlock(&priv->conf_mutex);
                up(&priv->scan.lock);
-               dev_kfree_skb(frame.skb);
                return ret;
        }
 
@@ -120,10 +120,9 @@ int cw1200_hw_scan(struct ieee80211_hw *hw,
                ++priv->scan.n_ssids;
        }
 
-       mutex_unlock(&priv->conf_mutex);
-
        if (frame.skb)
                dev_kfree_skb(frame.skb);
+       mutex_unlock(&priv->conf_mutex);
        queue_work(priv->workqueue, &priv->scan.work);
        return 0;
 }
-- 
2.19.1