nfc: Ensure presence of required attributes in the activate_target handler

Check that the NFC_ATTR_TARGET_INDEX and NFC_ATTR_PROTOCOLS attributes (in
addition to NFC_ATTR_DEVICE_INDEX) are provided by the netlink client
prior to accessing them. This prevents potential unhandled NULL pointer
dereference exceptions which can be triggered by malicious user-mode
programs, if they omit one or both of these attributes.
Signed-off-by: Mateusz Jurczyk <mjurczyk@google.com>
Acked-by: Kees Cook <keescook@chromium.org>
Signed-off-by: Samuel Ortiz <sameo@linux.intel.com>

net/nfc/netlink.c

@@ -907,7 +907,9 @@ static int nfc_genl_activate_target(struct sk_buff *skb, struct genl_info *info)
 	u32 device_idx, target_idx, protocol;
 	int rc;
 
-	if (!info->attrs[NFC_ATTR_DEVICE_INDEX])
+	if (!info->attrs[NFC_ATTR_DEVICE_INDEX] ||
+	    !info->attrs[NFC_ATTR_TARGET_INDEX] ||
+	    !info->attrs[NFC_ATTR_PROTOCOLS])
 		return -EINVAL;
 
 	device_idx = nla_get_u32(info->attrs[NFC_ATTR_DEVICE_INDEX]);