[034/118] wireless: regulatory: fix channel disabling race condition

Ben Hutchings
2013-05-10T14:27:59Z

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

commit 990de49f74e772b6db5208457b7aa712a5f4db86 upstream.

When a full scan 2.4 and 5 GHz scan is scheduled, but then the 2.4 GHz
part of the scan disables a 5.2 GHz channel due to, e.g. receiving
country or frequency information, that 5.2 GHz channel might already
be in the list of channels to scan next. Then, when the driver checks
if it should do a passive scan, that will return false and attempt an
active scan. This is not only wrong but can also lead to the iwlwifi
device firmware crashing since it checks regulatory as well.

Fix this by not setting the channel flags to just disabled but rather
OR'ing in the disabled flag. That way, even if the race happens, the
channel will be scanned passively which is still (mostly) correct.

Signed-off-by: Johannes Berg <johannes.berg@intel.com>
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>
---
net/wireless/reg.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)

--- a/net/wireless/reg.c
+++ b/net/wireless/reg.c
@@ -853,7 +853,7 @@ static void handle_channel(struct wiphy
return;

REG_DBG_PRINT("Disabling freq %d MHz\n", chan->center_freq);
- chan->flags = IEEE80211_CHAN_DISABLED;
+ chan->flags |= IEEE80211_CHAN_DISABLED;
return;
}