b43: stop format string leaking into error msgs

The module parameter "fwpostfix" is userspace controllable, unfiltered,
and is used to define the firmware filename. b43_do_request_fw() populates
ctx->errors[] on error, containing the firmware filename. b43err()
parses its arguments as a format string. For systems with b43 hardware,
this could lead to a uid-0 to ring-0 escalation.

CVE-2013-2852
Signed-off-by: Kees Cook <keescook@chromium.org>
Cc: stable@vger.kernel.org
Signed-off-by: John W. Linville <linville@tuxdriver.com>

drivers/net/wireless/b43/main.c

@@ -2458,7 +2458,7 @@ static void b43_request_firmware(struct work_struct *work)
 	for (i = 0; i < B43_NR_FWTYPES; i++) {
 		errmsg = ctx->errors[i];
 		if (strlen(errmsg))
-			b43err(dev->wl, errmsg);
+			b43err(dev->wl, "%s", errmsg);
 	}
 	b43_print_fw_helptext(dev->wl, 1);
 	goto out;