examples: nf-queue: fix api usage

1. struct nlattr *attr[NFQA_MAX+1] must be initialized.
   Otherwise, attr[FOO] might be non-null after parsing
   even if that attribute isn't present in the message.

2. mnl_attr_get_payload will never return NULL (if the
   attribute is NULL, it returns MNL_ATTR_HDRLEN.)

Signed-off-by: Florian Westphal <fw@strlen.de>

diff --git a/examples/nf-queue.c b/examples/nf-queue.c
index 4d56751..7adac21 100644 (file)
--- a/examples/nf-queue.c
+++ b/examples/nf-queue.c
@@ -31,12 +31,11 @@ nfq_hdr_put(char *buf, int type, uint32_t queue_num)
        return nlh;
 }
 
-static int
+static void
 nfq_send_verdict(int queue_num, uint32_t id)
 {
        char buf[MNL_SOCKET_BUFFER_SIZE];
        struct nlmsghdr *nlh;
-       int ret;
 
        nlh = nfq_hdr_put(buf, NFQNL_MSG_VERDICT, queue_num);
        nfq_nlmsg_verdict_put(nlh, id, NF_ACCEPT);
@@ -45,16 +44,15 @@ nfq_send_verdict(int queue_num, uint32_t id)
                perror("mnl_socket_send");
                exit(EXIT_FAILURE);
        }
-
-       return ret;
 }
 
 static int queue_cb(const struct nlmsghdr *nlh, void *data)
 {
        struct nfqnl_msg_packet_hdr *ph = NULL;
-       struct nlattr *attr[NFQA_MAX+1];
+       struct nlattr *attr[NFQA_MAX+1] = {};
        uint32_t id = 0;
        struct nfgenmsg *nfg;
+       uint16_t plen;
 
        if (nfq_nlmsg_parse(nlh, attr) < 0) {
                perror("problems parsing");
@@ -63,17 +61,19 @@ static int queue_cb(const struct nlmsghdr *nlh, void *data)
 
        nfg = mnl_nlmsg_get_payload(nlh);
 
-       ph = (struct nfqnl_msg_packet_hdr *)
-               mnl_attr_get_payload(attr[NFQA_PACKET_HDR]);
-       if (ph == NULL) {
-               perror("problems retrieving metaheader");
+       if (attr[NFQA_PACKET_HDR] == NULL) {
+               fputs("metaheader not set\n", stderr);
                return MNL_CB_ERROR;
        }
 
-       id = ntohl(ph->packet_id);
+       ph = mnl_attr_get_payload(attr[NFQA_PACKET_HDR]);
 
-       printf("packet received (id=%u hw=0x%04x hook=%u)\n",
-               id, ntohs(ph->hw_protocol), ph->hook);
+       plen = mnl_attr_get_payload_len(attr[NFQA_PAYLOAD]);
+       /* void *payload = mnl_attr_get_payload(attr[NFQA_PAYLOAD]); */
+
+       id = ntohl(ph->packet_id);
+       printf("packet received (id=%u hw=0x%04x hook=%u, payload len %u)\n",
+               id, ntohs(ph->hw_protocol), ph->hook, plen);
 
        nfq_send_verdict(ntohs(nfg->res_id), id);