[PATCH 4.9 24/60] staging: rtl8188eu: prevent an underflow in rtw_check_beacon_data()

[Greg Kroah-Hartman]

4.9-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Dan Carpenter <dan.carpen...@oracle.com>

commit 784047eb2d3405a35087af70cba46170c5576b25 upstream.

The "len" could be as low as -14 so we should check for negatives.

Fixes: 9a7fe54ddc3a ("staging: r8188eu: Add source files for new driver - part 
1")
Signed-off-by: Dan Carpenter <dan.carpen...@oracle.com>
Signed-off-by: Greg Kroah-Hartman <gre...@linuxfoundation.org>

---
 drivers/staging/rtl8188eu/core/rtw_ap.c |    2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

--- a/drivers/staging/rtl8188eu/core/rtw_ap.c
+++ b/drivers/staging/rtl8188eu/core/rtw_ap.c
@@ -890,7 +890,7 @@ int rtw_check_beacon_data(struct adapter
                return _FAIL;
 
 
-       if (len > MAX_IE_SZ)
+       if (len < 0 || len > MAX_IE_SZ)
                return _FAIL;
 
        pbss_network->IELength = len;