wpa_supplicant segfault in large WLAN

Matt Causey matt.causey at gmail.com
Thu Sep 26 14:45:55 EDT 2013


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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