Re: Null pointer dereference when station associates [introduced by 4.0.5?]

[Tom Hughes <tom@compton.nu>]

On 29/06/15 09:30, Tom Hughes wrote:
> On 29/06/15 09:14, Johannes Berg wrote:
>> On Sat, 2015-06-27 at 16:34 +0100, Tom Hughes wrote:
>>>
>>> Interestingly from what I can see this is trying to create a file
>>> for the station at a path something like:
>>>
>>> ieee80211/phy0/netdev:XXXX/stations/XXXXXX
>>
>> indeed.
>>
>>> but in my (currently working) boot under 4.0.4 there is no netdev
>>> directory under phy0 in debugfs... but then maybe that is the problem
>>> as well if the inode pointer was null?
>>>
>>
>> This is pretty strange - if the dentry pointer (sdata
>> ->debugfs.subdir_stations) was NULL or an ERR_PTR(), the code would
>> return pretty much immediately.
>>
>> So it looks like that pointer is valid, but it's ->d_inode was NULL?
>>
>> I'm not really sure how that could happen.
> 
> Indeed I'm a bit puzzled... 

It looks like hostapd has something to do with it... If I stop hostapd and
remove ath9k and then reprobe it then the netdev dir appears:

gosford [~] % sudo modprobe ath9k                     
gosford [~] % sudo ls /sys/kernel/debug/ieee80211/phy1
ath9k			 long_retry_limit  reset	      user_power
fragmentation_threshold  netdev:wlp2s0	   rts_threshold      wep_iv
ht40allow_map		 power		   short_retry_limit
hwflags			 queues		   statistics
keys			 rc		   total_ps_buffered

Then I start hostapd and it vanishes:

gosford [~] % sudo systemctl start hostapd
gosford [~] % sudo ls /sys/kernel/debug/ieee80211/phy1
ath9k			 keys		   rc		      statistics
fragmentation_threshold  long_retry_limit  reset	      total_ps_buffered
ht40allow_map		 power		   rts_threshold      user_power
hwflags			 queues		   short_retry_limit  wep_iv

Tom

-- 
Tom Hughes (tom@compton.nu)
http://compton.nu/