netfilter: move nf_send_resetX() code to nf_reject_ipvX modules

Move nf_send_reset() and nf_send_reset6() to nf_reject_ipv4 and
nf_reject_ipv6 respectively. This code is shared by x_tables and
nf_tables.

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

3 files changed, 172 insertions, 0 deletions

diff --git a/net/ipv6/netfilter/Kconfig b/net/ipv6/netfilter/Kconfig
index bb1a40db7be1..6af874fc187f 100644
--- a/net/ipv6/netfilter/Kconfig
+++ b/net/ipv6/netfilter/Kconfig
@@ -40,8 +40,13 @@ config NFT_CHAIN_ROUTE_IPV6
           fields such as the source, destination, flowlabel, hop-limit and
           the packet mark.
 
+config NF_REJECT_IPV6
+        tristate "IPv6 packet rejection"
+        default m if NETFILTER_ADVANCED=n
+
 config NFT_REJECT_IPV6
         depends on NF_TABLES_IPV6
+        select NF_REJECT_IPV6
         default NFT_REJECT
         tristate
 
@@ -208,6 +213,7 @@ config IP6_NF_FILTER
 config IP6_NF_TARGET_REJECT
         tristate "REJECT target support"
         depends on IP6_NF_FILTER
+        select NF_REJECT_IPV6
         default m if NETFILTER_ADVANCED=n
         help
           The REJECT target allows a filtering rule to specify that an ICMPv6
diff --git a/net/ipv6/netfilter/Makefile b/net/ipv6/netfilter/Makefile
index 0f7e5b3f328d..fbb25f01143c 100644
--- a/net/ipv6/netfilter/Makefile
+++ b/net/ipv6/netfilter/Makefile
@@ -27,6 +27,9 @@ obj-$(CONFIG_NF_DEFRAG_IPV6) += nf_defrag_ipv6.o
 # logging
 obj-$(CONFIG_NF_LOG_IPV6) += nf_log_ipv6.o
 
+# reject
+obj-$(CONFIG_NF_REJECT_IPV6) += nf_reject_ipv6.o
+
 # nf_tables
 obj-$(CONFIG_NF_TABLES_IPV6) += nf_tables_ipv6.o
 obj-$(CONFIG_NFT_CHAIN_ROUTE_IPV6) += nft_chain_route_ipv6.o
diff --git a/net/ipv6/netfilter/nf_reject_ipv6.c b/net/ipv6/netfilter/nf_reject_ipv6.c
new file mode 100644
index 000000000000..5f5f0438d74d
--- /dev/null
+++ b/net/ipv6/netfilter/nf_reject_ipv6.c
@@ -0,0 +1,163 @@
+/* (C) 1999-2001 Paul `Rusty' Russell
+ * (C) 2002-2004 Netfilter Core Team <coreteam@netfilter.org>
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License version 2 as
+ * published by the Free Software Foundation.
+ */
+#include <net/ipv6.h>
+#include <net/ip6_route.h>
+#include <net/ip6_fib.h>
+#include <net/ip6_checksum.h>
+#include <linux/netfilter_ipv6.h>
+
+void nf_send_reset6(struct net *net, struct sk_buff *oldskb, 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;
+        }
+
+        proto = oip6h->nexthdr;
+        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;
+        }
+
+        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 (skb_copy_bits(oldskb, tcphoff, &otcph, sizeof(struct tcphdr)))
+                BUG();
+
+        /* No RST for RST. */
+        if (otcph.rst) {
+                pr_debug("RST is set\n");
+                return;
+        }
+
+        /* 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;
+        }
+
+        skb_dst_set(nskb, dst);
+
+        skb_reserve(nskb, hh_len + dst->header_len);
+
+        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->saddr = oip6h->daddr;
+        ip6h->daddr = oip6h->saddr;
+
+        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;
+
+        if (otcph.ack) {
+                needs_ack = 0;
+                tcph->seq = otcph.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->seq = 0;
+        }
+
+        /* Reset flags */
+        ((u_int8_t *)tcph)[13] = 0;
+        tcph->rst = 1;
+        tcph->ack = needs_ack;
+        tcph->window = 0;
+        tcph->urg_ptr = 0;
+        tcph->check = 0;
+
+        /* Adjust TCP checksum */
+        tcph->check = csum_ipv6_magic(&ipv6_hdr(nskb)->saddr,
+                                      &ipv6_hdr(nskb)->daddr,
+                                      sizeof(struct tcphdr), IPPROTO_TCP,
+                                      csum_partial(tcph,
+                                                   sizeof(struct tcphdr), 0));
+
+        nf_ct_attach(nskb, oldskb);
+
+#if IS_ENABLED(CONFIG_BRIDGE_NETFILTER)
+        /* If we use ip6_local_out for bridged traffic, the MAC source on
+         * the RST will be ours, instead of the destination's.  This confuses
+         * some routers/firewalls, and they drop the packet.  So we need to
+         * build the eth header using the original destination's MAC as the
+         * source, and send the RST packet directly.
+         */
+        if (oldskb->nf_bridge) {
+                struct ethhdr *oeth = eth_hdr(oldskb);
+                nskb->dev = oldskb->nf_bridge->physindev;
+                nskb->protocol = htons(ETH_P_IPV6);
+                ip6h->payload_len = htons(sizeof(struct tcphdr));
+                if (dev_hard_header(nskb, nskb->dev, ntohs(nskb->protocol),
+                                    oeth->h_source, oeth->h_dest, nskb->len) < 0)
+                        return;
+                dev_queue_xmit(nskb);
+        } else
+#endif
+                ip6_local_out(nskb);
+}
+EXPORT_SYMBOL_GPL(nf_send_reset6);