libertas: fix buffer overrun

If somebody sends an invalid beacon/probe response, that can trash the
whole BSS descriptor. The descriptor is, luckily, large enough so that
it cannot scribble past the end of it; it's well above 400 bytes long.
Signed-off-by: NJohannes Berg <johannes@sipsolutions.net>
Cc: stable@kernel.org [2.6.24-2.6.27, bug present in some form since driver was added (2.6.22)]
Signed-off-by: NJohn W. Linville <linville@tuxdriver.com>

drivers/net/wireless/libertas/scan.c

@@ -598,8 +598,8 @@ static int lbs_process_bss(struct bss_descriptor *bss,
 
 		switch (elem->id) {
 		case MFIE_TYPE_SSID:
-			bss->ssid_len = elem->len;
-			memcpy(bss->ssid, elem->data, elem->len);
+			bss->ssid_len = min_t(int, 32, elem->len);
+			memcpy(bss->ssid, elem->data, bss->ssid_len);
 			lbs_deb_scan("got SSID IE: '%s', len %u\n",
 			             escape_essid(bss->ssid, bss->ssid_len),
 			             bss->ssid_len);