wpa_supplicant segfault in large WLAN
Matt Causey
matt.causey
Thu Sep 26 12:03:28 PDT 2013
Another detail that may or may not be of interest is that most of these
access points are 4x4:3 APs - which may or may not affect what's in the IE
on the beacons.
--
Matt
On Thu, Sep 26, 2013 at 2:45 PM, Matt Causey <matt.causey at gmail.com> wrote:
> On Thu, Sep 26, 2013 at 1:54 PM, Ben Greear <greearb at candelatech.com>wrote:
>
>> On 09/26/2013 09:13 AM, Matt Causey wrote:
>>
>> On Wed, Sep 25, 2013 at 6:58 PM, Ben Greear <greearb at candelatech.com<mailto:
>>> greearb at candelatech.**com <greearb at candelatech.com>>> wrote:
>>>
>>> On 09/25/2013 03:51 PM, Matt Causey wrote:
>>>
>>> Hello,
>>>
>>> We run wpa_supplicant on embedded machines and have today
>>> noticed that the supplicant dies with segmentation fault. We are seeing
>>> sporadic timeouts
>>> from the
>>> infrastructure as well, which may or may not be related. The
>>> only change on our side is that we installed in a very dense RF environment
>>> with a large
>>> number of
>>> BSSIDs. Are there any details pertaining to BSSID count or
>>> beacon count that could cause a segmentation fault? I'll start looking in
>>> the code but
>>> wanted to
>>> ask first so that hopefully someone can point me in a more
>>> useful direction. :-)
>>>
>>> Here is a log snippet. It's got to be abbreviated because in
>>> some cases we have over 988 BSSIDs visible from the client:
>>>
>>>
>>> Can you get a core dump and backtrace (and maybe more info from gdb
>>> once
>>> we see the backtrace?)
>>>
>>>
>>> OK so I did get some info. It might appear that there is some new
>>> Information Element in the beacons in this RF environment that's causing
>>> the segfault. Not sure:
>>>
>>> sudo gdb wpa_supplicant
>>> GNU gdb 6.8
>>> Copyright (C) 2008 Free Software Foundation, Inc.
>>> License GPLv3+: GNU GPL version 3 or later <http://gnu.org/licenses/gpl.
>>> **html <http://gnu.org/licenses/gpl.html>>
>>> This is free software: you are free to change and redistribute it.
>>> There is NO WARRANTY, to the extent permitted by law. Type "show
>>> copying"
>>> and "show warranty" for details.
>>> This GDB was configured as "i686-pc-linux-gnu"...
>>> (gdb) run -s -t -Dnl80211 -onl80211 -ddd -i wlan0 -c /var/tmp/nerf.conf
>>> Starting program: /usr/local/sbin/wpa_supplicant -s -t -Dnl80211
>>> -onl80211 -ddd -i wlan0 -c /var/tmp/nerf.conf
>>> [Thread debugging using libthread_db enabled]
>>> 1380211578.212081: ssid - hexdump_ascii(len=7):
>>> 61 73 69 6e 32 38 32 asin282
>>> 1380211578.212199: bgscan - hexdump_ascii(len=19):
>>> 73 69 6d 70 6c 65 3a 36 30 30 3a 2d 36 36 3a 31 simple:600:-66:1
>>> 32 30 30 200
>>> [removed]
>>> 1380211578.212699: private_key_passwd - hexdump_ascii(len=29): [REMOVED]
>>> 1380211578.335831: nl80211: Scan SSID - hexdump_ascii(len=0): [NULL]
>>>
>>> 1380211587.924526: * SSID - hexdump_ascii(len=7):
>>> 61 73 69 6e 32 38 32 asin282
>>> 1380211588.042745: nl80211: Scan SSID - hexdump_ascii(len=0): [NULL]
>>> 1380211589.147182: * SSID - hexdump_ascii(len=7):
>>> 61 73 69 6e 32 38 32 asin282
>>>
>>> 1380211589.247747: nl80211: Scan SSID - hexdump_ascii(len=0): [NULL]
>>> 1380211590.105423: * SSID - hexdump_ascii(len=7):
>>> 61 73 69 6e 32 38 32 asin282
>>> 1380211590.222784: nl80211: Scan SSID - hexdump_ascii(len=0): [NULL]
>>> [New Thread 0xb73dc6c0 (LWP 16180)]
>>>
>>> Program received signal SIGSEGV, Segmentation fault.
>>> [Switching to Thread 0xb73dc6c0 (LWP 16180)]
>>> wpa_bss_get_vendor_ie (bss=0x87c0a40, vendor_type=5304833) at bss.c:912
>>> 912 bss.c: No such file or directory.
>>> in bss.c
>>> (gdb)
>>> (gdb)
>>> (gdb)
>>>
>>>
>>> (gdb) bt
>>> #0 wpa_bss_get_vendor_ie (bss=0x87c0a40, vendor_type=5304833) at
>>> bss.c:912
>>> #1 0x08086de9 in wpas_select_network_from_last_**scan
>>> (wpa_s=0x876f468) at events.c:645
>>> #2 0x08087e23 in _wpa_supplicant_event_scan_**results
>>> (wpa_s=0x876f468, data=0xa) at events.c:1186
>>> #3 0x08087ed3 in wpa_supplicant_event_scan_**results (wpa_s=0x87cf000,
>>> data=0x0) at events.c:1269
>>> #4 0x0808893d in wpa_supplicant_event (ctx=0x876f468,
>>> event=EVENT_SCAN_RESULTS, data=0xbffbe438) at events.c:2438
>>> #5 0x08099371 in send_scan_event (drv=0x876ffb8, aborted=142320980,
>>> tb=0xbffbed50) at ../src/drivers/driver_nl80211.**c:1679
>>> #6 0x08099d4b in do_process_drv_event (bss=0x87700ac, cmd=34,
>>> tb=0xbffbed50) at ../src/drivers/driver_nl80211.**c:2201
>>> #7 0x0809a4fc in process_global_event (msg=0x87734d0, arg=0x876ff00) at
>>> ../src/drivers/driver_nl80211.**c:2346
>>> #8 0xb772c47c in nl_cb_call () from /usr/local/lib/libnl.so.1
>>> #9 0xb772cb7a in nl_recvmsgs () from /usr/local/lib/libnl.so.1
>>> #10 0x08055173 in eloop_sock_table_dispatch (table=0x80b8bc8,
>>> fds=0x877b2e8) at ../src/utils/eloop.c:393
>>> #11 0x08055a08 in eloop_run () at ../src/utils/eloop.c:769
>>> #12 0x0808163e in wpa_supplicant_run (global=0x876f388) at
>>> wpa_supplicant.c:3322
>>> #13 0x0808cc94 in main (argc=Cannot access memory at address 0x87cefff
>>> ) at main.c:297
>>> (gdb)
>>>
>>>
>>> Thoughts?
>>>
>>
>> Post a tarball of your source somewhere and/or show bss.c line 912 and
>> surrounding lines.
>>
>>
> Referencing the latest code, it's this line:
>
>
> http://hostap.epitest.fi/gitweb/gitweb.cgi?p=hostap.git;a=blob;f=wpa_supplicant/bss.c;h=0e1576b0fde1a71f2478665594631bac4fed28bf;hb=HEAD#l991
>
> Referencing wpa_supplicant-2.0, which we're using unmodified, here's the
> function:
>
>
> /**
> * wpa_bss_get_vendor_ie - Fetch a vendor information element from a BSS
> entry
> * @bss: BSS table entry
> * @vendor_type: Vendor type (four octets starting the IE payload)
> * Returns: Pointer to the information element (id field) or %NULL if not
> found
> *
> * This function returns the first matching information element in the BSS
> * entry.
> */
> const u8 * wpa_bss_get_vendor_ie(const struct wpa_bss *bss, u32
> vendor_type)
> {
> const u8 *end, *pos;
>
> pos = (const u8 *) (bss + 1);
> end = pos + bss->ie_len;
>
> while (pos + 1 < end) {
> if (pos + 2 + pos[1] > end) <-------- **LINE 912**
> break;
> if (pos[0] == WLAN_EID_VENDOR_SPECIFIC && pos[1] >= 4 &&
> vendor_type == WPA_GET_BE32(&pos[2]))
> return pos;
> pos += 2 + pos[1];
> }
>
> return NULL;
> }
>
> Cheers,
>
> --
> Matt
>
>
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