Staging: vt6655: fix buffer overflow

"param->u.wpa_associate.wpa_ie_len" comes from the user.  We should
check it so that the copy_from_user() doesn't overflow the buffer.

Also further down in the function, we assume that if
"param->u.wpa_associate.wpa_ie_len" is set then "abyWPAIE[0]" is
initialized.  To make that work, I changed the test here to say that if
"wpa_ie_len" is set then "wpa_ie" has to be a valid pointer or we return
-EINVAL.

Oddly, we only use the first element of the abyWPAIE[] array.  So I
suspect there may be some other issues in this function.

Signed-off-by: Dan Carpenter <error27@gmail.com>
Cc: stable <stable@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>

drivers/staging/vt6655/wpactl.c

diff --git a/drivers/staging/vt6655/wpactl.c b/drivers/staging/vt6655/wpactl.c
index 0142338b..4bdb836 100644
--- a/drivers/staging/vt6655/wpactl.c
+++ b/drivers/staging/vt6655/wpactl.c
@@ -766,9 +766,14 @@
     DBG_PRT(MSG_LEVEL_DEBUG, KERN_INFO "wpa_ie_len = %d\n", param->u.wpa_associate.wpa_ie_len);
 
 
-	if (param->u.wpa_associate.wpa_ie &&
-	    copy_from_user(&abyWPAIE[0], param->u.wpa_associate.wpa_ie, param->u.wpa_associate.wpa_ie_len))
-	    return -EINVAL;
+	if (param->u.wpa_associate.wpa_ie_len) {
+		if (!param->u.wpa_associate.wpa_ie)
+			return -EINVAL;
+		if (param->u.wpa_associate.wpa_ie_len > sizeof(abyWPAIE))
+			return -EINVAL;
+		if (copy_from_user(&abyWPAIE[0], param->u.wpa_associate.wpa_ie, param->u.wpa_associate.wpa_ie_len))
+			return -EFAULT;
+	}
 
 	if (param->u.wpa_associate.mode == 1)
 	    pMgmt->eConfigMode = WMAC_CONFIG_IBSS_STA;