netfilter: nf_reject_ipv6: split nf_send_reset6() in smaller functions

That can be reused by the reject bridge expression to build the reject
packet. The new functions are:

* nf_reject_ip6_tcphdr_get(): to sanitize and to obtain the TCP header.
* nf_reject_ip6hdr_put(): to build the IPv6 header.
* nf_reject_ip6_tcphdr_put(): to build the TCP header.

Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>

1 files changed, 109 insertions, 66 deletions

diff --git a/net/ipv6/netfilter/nf_reject_ipv6.c b/net/ipv6/netfilter/nf_reject_ipv6.c
index 20d9defc6c59..015eb8a80766 100644
--- a/net/ipv6/netfilter/nf_reject_ipv6.c
+++ b/net/ipv6/netfilter/nf_reject_ipv6.c
@@ -12,116 +12,102 @@
 #include <net/ip6_fib.h>
 #include <net/ip6_checksum.h>
 #include <linux/netfilter_ipv6.h>
+#include <net/netfilter/ipv6/nf_reject.h>
 
-void nf_send_reset6(struct net *net, struct sk_buff *oldskb, int hook)
+const struct tcphdr *nf_reject_ip6_tcphdr_get(struct sk_buff *oldskb,
+                                              struct tcphdr *otcph,
+                                              unsigned int *otcplen, int hook)
 {
-        struct sk_buff *nskb;
-        struct tcphdr otcph, *tcph;
-        unsigned int otcplen, hh_len;
-        int tcphoff, needs_ack;
         const struct ipv6hdr *oip6h = ipv6_hdr(oldskb);
-        struct ipv6hdr *ip6h;
-#define DEFAULT_TOS_VALUE       0x0U
-        const __u8 tclass = DEFAULT_TOS_VALUE;
-        struct dst_entry *dst = NULL;
         u8 proto;
         __be16 frag_off;
-        struct flowi6 fl6;
-
-        if ((!(ipv6_addr_type(&oip6h->saddr) & IPV6_ADDR_UNICAST)) ||
-            (!(ipv6_addr_type(&oip6h->daddr) & IPV6_ADDR_UNICAST))) {
-                pr_debug("addr is not unicast.\n");
-                return;
-        }
+        int tcphoff;
 
         proto = oip6h->nexthdr;
-        tcphoff = ipv6_skip_exthdr(oldskb, ((u8*)(oip6h+1) - oldskb->data), &proto, &frag_off);
+        tcphoff = ipv6_skip_exthdr(oldskb, ((u8*)(oip6h+1) - oldskb->data),
+                                   &proto, &frag_off);
 
         if ((tcphoff < 0) || (tcphoff > oldskb->len)) {
                 pr_debug("Cannot get TCP header.\n");
-                return;
+                return NULL;
         }
 
-        otcplen = oldskb->len - tcphoff;
+        *otcplen = oldskb->len - tcphoff;
 
         /* IP header checks: fragment, too short. */
-        if (proto != IPPROTO_TCP || otcplen < sizeof(struct tcphdr)) {
-                pr_debug("proto(%d) != IPPROTO_TCP, "
-                         "or too short. otcplen = %d\n",
-                         proto, otcplen);
-                return;
+        if (proto != IPPROTO_TCP || *otcplen < sizeof(struct tcphdr)) {
+                pr_debug("proto(%d) != IPPROTO_TCP or too short (len = %d)\n",
+                         proto, *otcplen);
+                return NULL;
         }
 
-        if (skb_copy_bits(oldskb, tcphoff, &otcph, sizeof(struct tcphdr)))
-                BUG();
+        otcph = skb_header_pointer(oldskb, tcphoff, sizeof(struct tcphdr),
+                                   otcph);
+        if (otcph == NULL)
+                return NULL;
 
         /* No RST for RST. */
-        if (otcph.rst) {
+        if (otcph->rst) {
                 pr_debug("RST is set\n");
-                return;
+                return NULL;
         }
 
         /* Check checksum. */
         if (nf_ip6_checksum(oldskb, hook, tcphoff, IPPROTO_TCP)) {
                 pr_debug("TCP checksum is invalid\n");
-                return;
-        }
-
-        memset(&fl6, 0, sizeof(fl6));
-        fl6.flowi6_proto = IPPROTO_TCP;
-        fl6.saddr = oip6h->daddr;
-        fl6.daddr = oip6h->saddr;
-        fl6.fl6_sport = otcph.dest;
-        fl6.fl6_dport = otcph.source;
-        security_skb_classify_flow(oldskb, flowi6_to_flowi(&fl6));
-        dst = ip6_route_output(net, NULL, &fl6);
-        if (dst == NULL || dst->error) {
-                dst_release(dst);
-                return;
-        }
-        dst = xfrm_lookup(net, dst, flowi6_to_flowi(&fl6), NULL, 0);
-        if (IS_ERR(dst))
-                return;
-
-        hh_len = (dst->dev->hard_header_len + 15)&~15;
-        nskb = alloc_skb(hh_len + 15 + dst->header_len + sizeof(struct ipv6hdr)
-                         + sizeof(struct tcphdr) + dst->trailer_len,
-                         GFP_ATOMIC);
-
-        if (!nskb) {
-                net_dbg_ratelimited("cannot alloc skb\n");
-                dst_release(dst);
-                return;
+                return NULL;
         }
 
-        skb_dst_set(nskb, dst);
+        return otcph;
+}
+EXPORT_SYMBOL_GPL(nf_reject_ip6_tcphdr_get);
 
-        skb_reserve(nskb, hh_len + dst->header_len);
+struct ipv6hdr *nf_reject_ip6hdr_put(struct sk_buff *nskb,
+                                     const struct sk_buff *oldskb,
+                                     __be16 protocol, int hoplimit)
+{
+        struct ipv6hdr *ip6h;
+        const struct ipv6hdr *oip6h = ipv6_hdr(oldskb);
+#define DEFAULT_TOS_VALUE       0x0U
+        const __u8 tclass = DEFAULT_TOS_VALUE;
 
         skb_put(nskb, sizeof(struct ipv6hdr));
         skb_reset_network_header(nskb);
         ip6h = ipv6_hdr(nskb);
         ip6_flow_hdr(ip6h, tclass, 0);
-        ip6h->hop_limit = ip6_dst_hoplimit(dst);
-        ip6h->nexthdr = IPPROTO_TCP;
+        ip6h->hop_limit = hoplimit;
+        ip6h->nexthdr = protocol;
         ip6h->saddr = oip6h->daddr;
         ip6h->daddr = oip6h->saddr;
 
+        nskb->protocol = htons(ETH_P_IPV6);
+
+        return ip6h;
+}
+EXPORT_SYMBOL_GPL(nf_reject_ip6hdr_put);
+
+void nf_reject_ip6_tcphdr_put(struct sk_buff *nskb,
+                              const struct sk_buff *oldskb,
+                              const struct tcphdr *oth, unsigned int otcplen)
+{
+        struct tcphdr *tcph;
+        int needs_ack;
+
         skb_reset_transport_header(nskb);
         tcph = (struct tcphdr *)skb_put(nskb, sizeof(struct tcphdr));
         /* Truncate to length (no data) */
         tcph->doff = sizeof(struct tcphdr)/4;
-        tcph->source = otcph.dest;
-        tcph->dest = otcph.source;
+        tcph->source = oth->dest;
+        tcph->dest = oth->source;
 
-        if (otcph.ack) {
+        if (oth->ack) {
                 needs_ack = 0;
-                tcph->seq = otcph.ack_seq;
+                tcph->seq = oth->ack_seq;
                 tcph->ack_seq = 0;
         } else {
                 needs_ack = 1;
-                tcph->ack_seq = htonl(ntohl(otcph.seq) + otcph.syn + otcph.fin
-                                      + otcplen - (otcph.doff<<2));
+                tcph->ack_seq = htonl(ntohl(oth->seq) + oth->syn + oth->fin +
+                                      otcplen - (oth->doff<<2));
                 tcph->seq = 0;
         }
 
@@ -139,6 +125,63 @@ void nf_send_reset6(struct net *net, struct sk_buff *oldskb, int hook)
                                       sizeof(struct tcphdr), IPPROTO_TCP,
                                       csum_partial(tcph,
                                                    sizeof(struct tcphdr), 0));
+}
+EXPORT_SYMBOL_GPL(nf_reject_ip6_tcphdr_put);
+
+void nf_send_reset6(struct net *net, struct sk_buff *oldskb, int hook)
+{
+        struct sk_buff *nskb;
+        struct tcphdr _otcph;
+        const struct tcphdr *otcph;
+        unsigned int otcplen, hh_len;
+        const struct ipv6hdr *oip6h = ipv6_hdr(oldskb);
+        struct ipv6hdr *ip6h;
+        struct dst_entry *dst = NULL;
+        struct flowi6 fl6;
+
+        if ((!(ipv6_addr_type(&oip6h->saddr) & IPV6_ADDR_UNICAST)) ||
+            (!(ipv6_addr_type(&oip6h->daddr) & IPV6_ADDR_UNICAST))) {
+                pr_debug("addr is not unicast.\n");
+                return;
+        }
+
+        otcph = nf_reject_ip6_tcphdr_get(oldskb, &_otcph, &otcplen, hook);
+        if (!otcph)
+                return;
+
+        memset(&fl6, 0, sizeof(fl6));
+        fl6.flowi6_proto = IPPROTO_TCP;
+        fl6.saddr = oip6h->daddr;
+        fl6.daddr = oip6h->saddr;
+        fl6.fl6_sport = otcph->dest;
+        fl6.fl6_dport = otcph->source;
+        security_skb_classify_flow(oldskb, flowi6_to_flowi(&fl6));
+        dst = ip6_route_output(net, NULL, &fl6);
+        if (dst == NULL || dst->error) {
+                dst_release(dst);
+                return;
+        }
+        dst = xfrm_lookup(net, dst, flowi6_to_flowi(&fl6), NULL, 0);
+        if (IS_ERR(dst))
+                return;
+
+        hh_len = (dst->dev->hard_header_len + 15)&~15;
+        nskb = alloc_skb(hh_len + 15 + dst->header_len + sizeof(struct ipv6hdr)
+                         + sizeof(struct tcphdr) + dst->trailer_len,
+                         GFP_ATOMIC);
+
+        if (!nskb) {
+                net_dbg_ratelimited("cannot alloc skb\n");
+                dst_release(dst);
+                return;
+        }
+
+        skb_dst_set(nskb, dst);
+
+        skb_reserve(nskb, hh_len + dst->header_len);
+        ip6h = nf_reject_ip6hdr_put(nskb, oldskb, IPPROTO_TCP,
+                                    ip6_dst_hoplimit(dst));
+        nf_reject_ip6_tcphdr_put(nskb, oldskb, otcph, otcplen);
 
         nf_ct_attach(nskb, oldskb);