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The length field of wext data (iw_point.data) is 16 bits. The largest
value is thus 65535. During the attempts to increase buffer size the
buffer starts at 4096 and is doubled after each failure to fill. From the
time this length reaches 65536 it is effectively zero. We thus loose all
potential space from 32768 to 65535.
This problem is clear when scanning in a RF dense environment.
Without this patch:
~$ iwlist wlan0 scan
print_scanning_info: Allocation failed
With this patch:
~$ iwlist wlan0 scan | grep Cell | wc -l
86
Signed-off-by: Reinette Chatre <reinette.chatre@intel.com>
---
A similar patch was recently created to fix wpa_supplicant.
I could not find a source code repo for this code and created this patch
against version 30-pre7 downloaded from
http://www.hpl.hp.com/personal/Jean_Tourrilhes/Linux/Tools.html
diff -uprN wireless_tools_org/wireless_tools.30/iwlist.c wireless_tools.30/iwlist.c
--- wireless_tools_org/wireless_tools.30/iwlist.c 2008-01-16 17:45:41.000000000 -0800
+++ wireless_tools.30/iwlist.c 2009-02-12 14:16:48.000000000 -0800
@@ -800,7 +800,7 @@ print_scanning_info(int skfd,
if(iw_get_ext(skfd, ifname, SIOCGIWSCAN, &wrq) < 0)
{
/* Check if buffer was too small (WE-17 only) */
- if((errno == E2BIG) && (range.we_version_compiled > 16))
+ if((errno == E2BIG) && (range.we_version_compiled > 16) && (buflen < 65535))
{
/* Some driver may return very large scan results, either
* because there are many cells, or because they have many
@@ -816,6 +816,10 @@ print_scanning_info(int skfd,
else
buflen *= 2;
+ /* wrq.u.data.length is 16 bits so max size is 65535 */
+ if(buflen > 65535)
+ buflen = 65535;
+
/* Try again */
goto realloc;
}
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