#include <linux/netfilter/nf_conntrack_common.h>
 
-extern const char *pptp_msg_name[];
+extern const char *const pptp_msg_name[];
 
 /* state of the control session */
 enum pptp_ctrlsess_state {
 
 static void pptp_nat_expected(struct nf_conn *ct,
                              struct nf_conntrack_expect *exp)
 {
-       struct nf_conn *master = ct->master;
+       const struct nf_conn *master = ct->master;
        struct nf_conntrack_expect *other_exp;
        struct nf_conntrack_tuple t;
-       struct nf_ct_pptp_master *ct_pptp_info;
-       struct nf_nat_pptp *nat_pptp_info;
+       const struct nf_ct_pptp_master *ct_pptp_info;
+       const struct nf_nat_pptp *nat_pptp_info;
        struct nf_nat_range range;
 
        ct_pptp_info = &nfct_help(master)->help.ct_pptp_info;
 pptp_exp_gre(struct nf_conntrack_expect *expect_orig,
             struct nf_conntrack_expect *expect_reply)
 {
-       struct nf_conn *ct = expect_orig->master;
+       const struct nf_conn *ct = expect_orig->master;
        struct nf_ct_pptp_master *ct_pptp_info;
        struct nf_nat_pptp *nat_pptp_info;
 
                 struct PptpControlHeader *ctlh,
                 union pptp_ctrl_union *pptpReq)
 {
-       struct nf_nat_pptp *nat_pptp_info;
+       const struct nf_nat_pptp *nat_pptp_info;
        u_int16_t msg;
        __be16 new_pcid;
        unsigned int pcid_off;
 
 
 #ifdef DEBUG
 /* PptpControlMessageType names */
-const char *pptp_msg_name[] = {
+const char *const pptp_msg_name[] = {
        "UNKNOWN_MESSAGE",
        "START_SESSION_REQUEST",
        "START_SESSION_REPLY",
 
 static int destroy_sibling_or_exp(const struct nf_conntrack_tuple *t)
 {
-       struct nf_conntrack_tuple_hash *h;
+       const struct nf_conntrack_tuple_hash *h;
        struct nf_conntrack_expect *exp;
        struct nf_conn *sibling;
 
 /* timeout GRE data connections */
 static void pptp_destroy_siblings(struct nf_conn *ct)
 {
-       struct nf_conn_help *help = nfct_help(ct);
+       const struct nf_conn_help *help = nfct_help(ct);
        struct nf_conntrack_tuple t;
 
        nf_ct_gre_keymap_destroy(ct);
 
 {
        int dir = CTINFO2DIR(ctinfo);
-       struct nf_ct_pptp_master *info = &nfct_help(ct)->help.ct_pptp_info;
-       struct tcphdr _tcph, *tcph;
-       struct pptp_pkt_hdr _pptph, *pptph;
+       const struct nf_ct_pptp_master *info = &nfct_help(ct)->help.ct_pptp_info;
+       const struct tcphdr *tcph;
+       struct tcphdr _tcph;
+       const struct pptp_pkt_hdr *pptph;
+       struct pptp_pkt_hdr _pptph;
        struct PptpControlHeader _ctlh, *ctlh;
        union pptp_ctrl_union _pptpReq, *pptpReq;
        unsigned int tcplen = skb->len - protoff;