cfg80211: fix deadlock with rfkill/sched_scan by adding new mutex

There was a deadlock when rfkill-blocking a wireless interface,
because we were locking the rdev mutex on NETDEV_GOING_DOWN to stop
sched_scans that were eventually running.  The rfkill block code was
already holding a mutex under rdev:

kernel: =======================================================
kernel: [ INFO: possible circular locking dependency detected ]
kernel: 3.0.0-rc1-00049-g1fa7b6a #57
kernel: -------------------------------------------------------
kernel: kworker/0:1/4525 is trying to acquire lock:
kernel: (&rdev->mtx){+.+.+.}, at: [<ffffffff8164c831>] cfg80211_netdev_notifier_call+0x131/0x5b0
kernel:
kernel: but task is already holding lock:
kernel: (&rdev->devlist_mtx){+.+.+.}, at: [<ffffffff8164dcef>] cfg80211_rfkill_set_block+0x4f/0xa0
kernel:
kernel: which lock already depends on the new lock.

To fix this, add a new mutex specifically for sched_scan, to protect
the sched_scan_req element in the rdev struct, instead of using the
global rdev mutex.

Reported-by: Duane Griffin <duaneg@dghda.com>
Signed-off-by: Luciano Coelho <coelho@ti.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>

1 files changed, 18 insertions, 6 deletions

diff --git a/net/wireless/nl80211.c b/net/wireless/nl80211.c
index f07602d7bf6..cea338150d0 100644
--- a/net/wireless/nl80211.c
+++ b/net/wireless/nl80211.c
@@ -3461,9 +3461,6 @@ static int nl80211_start_sched_scan(struct sk_buff *skb,
         if (!is_valid_ie_attr(info->attrs[NL80211_ATTR_IE]))
                 return -EINVAL;
 
-        if (rdev->sched_scan_req)
-                return -EINPROGRESS;
-
         if (!info->attrs[NL80211_ATTR_SCHED_SCAN_INTERVAL])
                 return -EINVAL;
 
@@ -3502,12 +3499,21 @@ static int nl80211_start_sched_scan(struct sk_buff *skb,
         if (ie_len > wiphy->max_scan_ie_len)
                 return -EINVAL;
 
+        mutex_lock(&rdev->sched_scan_mtx);
+
+        if (rdev->sched_scan_req) {
+                err = -EINPROGRESS;
+                goto out;
+        }
+
         request = kzalloc(sizeof(*request)
                         + sizeof(*request->ssids) * n_ssids
                         + sizeof(*request->channels) * n_channels
                         + ie_len, GFP_KERNEL);
-        if (!request)
-                return -ENOMEM;
+        if (!request) {
+                err = -ENOMEM;
+                goto out;
+        }
 
         if (n_ssids)
                 request->ssids = (void *)&request->channels[n_channels];
@@ -3605,6 +3611,7 @@ static int nl80211_start_sched_scan(struct sk_buff *skb,
 out_free:
         kfree(request);
 out:
+        mutex_unlock(&rdev->sched_scan_mtx);
         return err;
 }
 
@@ -3612,12 +3619,17 @@ static int nl80211_stop_sched_scan(struct sk_buff *skb,
                                    struct genl_info *info)
 {
         struct cfg80211_registered_device *rdev = info->user_ptr[0];
+        int err;
 
         if (!(rdev->wiphy.flags & WIPHY_FLAG_SUPPORTS_SCHED_SCAN) ||
             !rdev->ops->sched_scan_stop)
                 return -EOPNOTSUPP;
 
-        return __cfg80211_stop_sched_scan(rdev, false);
+        mutex_lock(&rdev->sched_scan_mtx);
+        err = __cfg80211_stop_sched_scan(rdev, false);
+        mutex_unlock(&rdev->sched_scan_mtx);
+
+        return err;
 }
 
 static int nl80211_send_bss(struct sk_buff *msg, u32 pid, u32 seq, int flags,