Hi,
some time ago I had an issue with a wireless device that it couldn't
associate to the AP over some time. I found out that the BSS with the
corresponding SSID was the last in the scan list and was truncated - all
the IEs were missing and so the supplicant did not detect that it
supports WPA2 and hence ignored it.
After some playing with different wireless devices I discovered that
this is not limited to specific drivers so I digged a bit in the scan
code in net/wireless/scan.c and found the culprit: The scan result is
put together with the iwe_stream_* functions that place data into a
provided buffer if enough space is available in the buffer. Otherwise
the functions do just nothing. Before a BSS is added there is a check if
some minimum space is available but after the BSS has been added it is
not clear how many data actually has been placed into the buffer. So
especially (but not neccessarily only) the last BSS is prone to be
incomplete. I my case all the IEs were missing and this was persistent
over some time (the persitence behavior seems to differs between drivers
- probably depends on how the scanning is implemented).
Currently I implemented a heuristic that checks if some minimum space
(currently 256 bytes) is still free _after_ adding a BSS and otherwise
return -E2BIG so the user space can provide a larger buffer but this is
a crappy hack.
Can the code be changed in some way to more reliably detect if some data
did not fit into the buffer and report this to user space?
- ron
--
Ronald Wahl - ronald.wahl@xxxxxxxxxxx - Phone +49 375271349-0 Fax -99
Raritan Deutschland GmbH, Kornmarkt 7, 08056 Zwickau, Germany
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Geschäftsführung: Stuart Hopper, Burkhard Wessler
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